JPS6269159A - Control device for air fuel-ratio of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the generation of a blackening phenomenon and also to prevent an oxygen pump element from being deteriorated quickly, by stop-ping the discrimination of an air-fuel ratio at the time of a prescribed operation state, and also stopping a current supply to the oxygen pump element. CONSTITUTION:An oxygen concentration sensor 19 has an oxygen pump element 26 and a battery element 27 being a pair of plate-shaped elements which are parallel to each other, and the main body of the elements 26, 27 consists of an oxygen ion conductive solid-state electrolytic material. Between electrode plates 30, 31 of the element 26, a current is supplied by a constant-current circuit 40. Also, a voltage which is generated between electrodes 32, 33 of the element 27 is amplified 43, supplied to an air-fuel ratio control device 21 as the output voltage of the sensor 19, the air-fuel ratio of an air-fuel mixture supplied to an engine is discriminated, and in accordance with its result, the air-fuel ratio of the supplied air-fuel mixture is adjusted. Also, when the engine stops an air-fuel ratio feedback control and becomes an operation state which is to be subjected to an open loop control, for instance, an operation state which requires the increase of the quantity of fuel, and decelerating and accelerating operation states, the discrimination of the air-fuel ratio is stopped, and also the current supply to the element 26 is stopped.

Description

[Detailed description of the invention] Enkyodate 1 The present invention relates to an air-fuel ratio control device for an internal combustion engine.

11 In order to purify the exhaust gas of internal combustion engines and improve fuel efficiency, the elemental concentration in the exhaust gas is detected, and the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled to the target air-fuel ratio according to the detection results. There is an air-fuel ratio control device that does this.

As an oxygen concentration sensor used in such an air-fuel ratio control device, there is one that generates an output proportional to the oxygen concentration in the exhaust gas in a region where the air-fuel ratio of 'fiR Aiki supplied to the engine is greater than the stoichiometric air-fuel ratio. (Unexamined Japanese Patent Publication No. 58-15
No. 3155). Such an oxygen concentration sensor is provided with an oxygen concentration detector having a pair of flat oxygen ion conductive solid electrolyte members. The solid electrolyte member is arranged in exhaust gas, and electrodes are formed on each front and back surface of the solid electrolyte member, and the solid electrolyte members are arranged in parallel so as to face each other with a predetermined gap in between. ing. One of the solid electrolyte members acts as an oxygen pump element, and the other acts as a battery element for oxygen concentration ratio measurement. When a current is supplied between the electrodes of the oxygen pump element such that the electrode on the gap side becomes the negative electrode in the exhaust gas, the oxygen gas in the gap is ionized on the negative electrode side of the oxygen pump element, and the oxygen pump element The oxygen gas moves to the positive electrode surface and is released as oxygen gas from the positive electrode surface.

At this time, due to the decrease in oxygen gas in the gap, a difference in oxygen concentration occurs between the gas in the gap and the gas outside the battery element, so if the current supplied to the oxygen pump element, that is, the pump current value, is constant, the battery The difference in oxygen concentration between the electrodes of the element,
In other words, a voltage proportional to the oxygen concentration in the exhaust gas is generated. Based on the voltage generated by the battery element, it is determined whether the air-fuel ratio of the air-fuel mixture supplied to the engine is ridge or lean compared to the target air-fuel ratio. When controlling the air-fuel ratio using secondary air, if it is determined to be lip, secondary air is supplied to the engine, and if it is determined to be lean,
By stopping and increasing the supply of secondary air, the air-fuel ratio is controlled to the target air-fuel ratio. Furthermore, if the pump current value supplied to the oxygen pump element is changed to keep the voltage generated by the battery element constant, the current value will be approximately proportional to the oxygen concentration in the exhaust gas at a constant temperature, and the pump current value will be approximately proportional to the oxygen concentration in the exhaust gas. It is also possible to determine the air-fuel ratio.

In such an oxygen concentration detection device, when an excessive current is supplied to the oxygen pump element, a blackening phenomenon occurs in which oxygen is taken away from the solid electrolyte material.

For example, when ZrO2 (zirconium dioxide) is used as the solid electrolyte material, oxygen 02 is taken away from ZrO2 by excessive current supply to the oxygen pump element, and zirconium Zr is deposited. This blackening phenomenon causes rapid deterioration of the oxygen pump element and deteriorates its performance as an oxygen concentration detector.

FIG. 1 shows the relationship between the oxygen concentration and the current value 1p supplied to the oxygen pump element and the region where the blackening phenomenon occurs, using the voltage Vs generated in the battery element as a parameter.
Since the boundary line with the blackening phenomenon occurrence region is a linear functional characteristic similar to the relational characteristic using the voltage Vs as a parameter, does the current supplied from the voltage Vs to the oxygen pump element belong to the value of the blackening phenomenon occurrence region? It can be determined whether or not. Therefore, when the voltage Vs rises to a voltage that is slightly smaller than the boundary voltage of the area where the blackening phenomenon occurs, the current supplied to the oxygen pump element becomes a value close to the area where the blackening phenomenon occurs, and by reducing the supply current, the black is removed. This makes it possible to prevent the occurrence of the ning phenomenon.

In an air-fuel ratio control device using such an oxygen concentration sensor, the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled to a target air-fuel ratio that is greater than the stoichiometric air-fuel ratio (14, 7). When the air-fuel ratio of the supplied air-fuel mixture changes to the stoichiometric air-fuel ratio when the feedback control such as acceleration or deceleration is stopped and the air-fuel ratio is shifted from the operating state that should be in a feedback control state such as steady operation to the operating state that requires open-loop control of the air-fuel ratio. A situation occurs where the air-fuel ratio is close to or smaller than the stoichiometric air-fuel ratio. However, as the air-fuel ratio becomes richer, that is, as the M-line concentration decreases, the blackening phenomenon occurrence boundary value becomes smaller. There has been a problem in that the value of the current supplied to the wire may exceed the boundary value for the occurrence of blackening, resulting in a blackening phenomenon.

Therefore, an object of the present invention is to provide an air-fuel ratio control device that can prevent the blackening phenomenon from occurring when the operating state is shifted from an operating state where air-fuel ratio feedback control is required to an operating state where oven loop control is required. It is to provide.

The air-fuel ratio control device of the present invention is characterized in that it stops determining the air-fuel ratio and stops supplying current to the oxygen pump element when the engine is in a predetermined operating state.

叉-”L-father-in-law Embodiments of the present invention will be described below with reference to the drawings.

In the air-fuel ratio control device which is an embodiment of the present invention shown in FIG.
, carburetor 3, and intake manifold 4 to the engine 5. The vaporizer 3 is provided with a throttle valve 6,
A venturi 7 is formed upstream of the throttle valve 6.

A main nozzle 8 of the main fuel supply system of the carburetor 3 opens into the venturi 7, and a main fuel passage 9 communicating with the main nozzle 8 is provided with a main jet 10. An auxiliary fuel passage 11 is formed so as to bypass this main jet 10 and communicate with a float chamber (not shown), and a power valve 12 is provided in the auxiliary fuel passage 11. The power valve 12 has a solenoid, and opens when the solenoid is energized.

The intake manifold 4 and the vicinity of the air discharge port of the air cleaner 2 are communicated through an intake secondary air supply passage 13. An electromagnetic on-off valve 14 is provided in the intake secondary air supply passage 13 . Electromagnetic l? 1 closing valve 14 is its solenoid 14
The valve opens when electricity is applied to a.

On the other hand, 15 is an absolute pressure range provided in the intake manifold 4 and generates an output at a level corresponding to the absolute pressure inside the intake manifold 4, and 16 is the crankshaft of the engine 5 (
A crank angle sensor 17 generates pulses according to the rotation of the engine (not shown), and a cooling water temperature sensor 17 generates an output at a level corresponding to the cooling water temperature of the engine 5. Further, reference numeral 18 is an intake air temperature sensor that is installed near the air intake port 1 and generates an output at a level corresponding to the intake air temperature, and 19 is an intake air temperature sensor that is installed on the exhaust manifold 20 of the engine 5 and outputs an output that is proportional to the MX concentration in the exhaust gas. It is a lean oxygen a degree sensor that generates an output. A catalytic converter 25 is provided in the exhaust manifold 20 downstream of the oxygen concentration sensor 19 in order to promote reduction of harmful components in the exhaust gas. Electromagnetic on-off valve 14, absolute pressure sensor 15, crank angle sensor 16, water temperature sensor 17, intake temperature sensor 18, and oxygen concentration sensor 19
is connected to the air-fuel ratio control circuit 21. Control circuit 21
Furthermore, there is a vehicle speed sensor 22 that generates an output at a level corresponding to the speed of the vehicle, a clutch switch 23 that is turned on when the vehicle's clutch is released and outputs a predetermined voltage, and a gear shift lever of a five-speed manual transmission. A neutral switch 24 that is turned on and outputs a predetermined voltage when in the neutral position is connected.

As shown in FIG. 3, the oxygen concentration sensor 19 consists of a pair of parallel flat elements including an oxygen pump element 26 and a battery element 2.
7. Oxygen pump element 26 and battery cable 27
The main body is made of an oxygen ion conductive solid electrolyte material, and a gap 28 is formed between one end thereof, and the other end is made of a solid electrolyte material that conducts oxygen ions.
They are coupled to each other via j29. Further, rectangular electrode plates 30 to 33 made of porous heat-resistant metal are provided on the front and back surfaces of one end of the oxygen pump element 26 and the battery element 27, and the lead wires 30a of the electrode plates 30 to 33 are provided on the other end surface. 33a are formed.

The control section of the oxygen concentration sensor 19 is a constant current circuit 40
, limiter circuit 41, programmable voltage generation circuit 42
and a non-inverting amplifier 43.

A current is supplied between the electrode plates 30 and 31 of the oxygen pump element 26 by a constant current circuit 40. The constant current circuit 40 includes an operational amplifier 44. NPN transistor 45, diode 46
and resistors 47 to 50. The output terminal of the operational amplifier 44 is connected to the base of a transistor 45 via a resistor 47.

Further, the emitter of the transistor 45 is grounded via a resistor 48, connected to the inverting input terminal of the operational amplifier 44 via a resistor 49, and further connected to the output terminal of the operational amplifier 44 via a diode 46 in the forward direction. . The resistor 48 is provided to detect the pump current value Iρ flowing between the electrode plates 30 and 31 of the oxygen pump element 26.

The collector of the transistor 45 is connected to the inner electrode plate 31 of the oxygen pump element 26 via a lead wire 31a, and a voltage 8 is supplied to the outer electrode plate 30 via the lead wire 30a.

A non-inverting input terminal of the operational amplifier 44 is connected to the programmable voltage generation circuit 42 via a resistor 50. The programmable voltage generation circuit 42 generates a voltage according to Ip [command data] output from the air-fuel ratio control circuit 21.

On the other hand, the inner electrode plate 32 of the battery element 27 is connected to the lead wire 32.
a, and the outer electrode plate 33 is connected to the lead wire 3.
The operational amplifier 51.3a is connected to the operational amplifier 51.3a. It is connected to a non-inverting amplifier 43 consisting of resistors 52-54. The output terminal of the non-inverting amplifier 43 is connected to the air-fuel ratio control circuit 21.

Further, the output terminal of the non-inverting amplifier 43 is connected to the limiter circuit 41. The limiter circuit 41 includes an operational amplifier 55, resistors 56 to 59, a variable resistor 60, and a diode 61.
Consisting of The resistors 56 and 57 and the variable resistor 60 are connected in series to form a voltage dividing circuit 62 that outputs a divided voltage of the voltage Vs as the limiter reference voltage VL, and the movable end of the variable resistor 60, which is the divided voltage output terminal, is connected in series. is connected to the inverting input terminal of the operational amplifier 55. A voltage corresponding to the difference voltage between the output voltage of the inverting amplifier 43 and the voltage divided by the voltage dividing circuit 62 is applied to the non-inverting input terminal of the operational amplifier 55 from the output terminal of the operational amplifier 55 through the resistor 58 and the diode 61 in the forward direction. The signal is supplied to the inverting input terminal of the operational amplifier 44.

As shown in FIG. 4, the control circuit 21 includes an absolute pressure sensor 15, a water temperature sensor 17, an intake temperature sensor 18, and an oxygen concentration sensor 19.
and a level conversion circuit 71 that converts each output level of the vehicle speed sensor 4) 22, a multiplexer 72 that selectively outputs one of the outputs of each sensor that has passed through the level conversion circuit 71, and a signal output from this multiplexer 72. an A/D converter 73 that converts the signal into a digital signal; a waveform shaping circuit 74 that shapes the output signal of the crank angle sensor 16; and a waveform shaping circuit 74 that measures the generation interval of the TDC signal output as a pulse from the waveform shaping circuit 74. A counter 75, a level conversion circuit 76 that converts each output level of the clutch switch 23 and neutral switch 24, a digital input camosulator 77 that converts each switch output via the level conversion circuit 76 into digital data, and a power valve 12 or electromagnetic opening/closing Drive circuits 78 and 79 that drive the valve 14 to open, a CPtJ (central processing circuit) 80 that performs digital calculations according to programs, a ROM 81 and a RAM 82 in which various processing programs and data are written in advance, and a RAM 82 that stores Ip command data. A latch circuit for holding the circuit 84 is connected to the circuit 84. Multi-brake ratio 72, A/D transmission 73, counter 75, digital input camosulator 77, drive circuit 7
8, 79, CPtJ80, ROM8L RAM82, and latch circuit 84 are connected to each other by an input/output bus 83.

In this configuration, when the Iρ value command data is output from the air-fuel ratio control circuit 21 to the programmable electric generator circuit 42, the programmable voltage generator circuit 42 converts the voltage corresponding to the IP value command data into the reference voltage V r +. −
It is supplied to the non-inverting input terminal of the operational amplifier 44 via the 7Tlt resistor 50. , the pump current value 1p flowing through the electrode plates 30, 31 of the M-element pump element 26 when the reference voltage V r' is supplied to the inverting input terminal of When the terminal voltage Vp is lower than the reference voltage Vr+, the output level of the operational amplifier 44 becomes high level and increases the base current of the transistor 45, thereby increasing the pump current. The output level will throb low, reducing the base current of transistor 45 and thus lowering the pump current. Since this operation is repeated at high speed, the pump current IP has a constant current value according to the reference voltage Vr+.

On the other hand, a voltage Vs is applied between the electrode plates 32 and 33 of the battery element 27.
is generated, and the voltage Vs is amplified by the non-inverting amplifier 43 and supplied to the air-fuel ratio control circuit 21 as the output voltage Vs= of the oxygen concentration sensor 19.

Here, if the air-fuel ratio of the air-fuel mixture supplied to the engine fluctuates around the stoichiometric air-fuel ratio, then the electrode plates 32.3 of the battery element 27
3, and the output voltage Vs'' of the non-inverting amplifier 43 also collapses.When the output voltage Vs- exceeds the limiter reference voltage VL, the output voltage Vs- and the limiter reference voltage VL
Since the voltage corresponding to the voltage difference between the terminal voltage Vp and the terminal voltage Vp is higher than the terminal voltage Vp, the resistor 58. Diode 61. A current flows through resistor 49 and resistor /I8 to raise the voltage at the inverting input terminal of operational amplifier 44 above reference voltage Vr+. Therefore, the output voltage of the operational amplifier 44 decreases, the base current of the transistor 45 decreases, and the pump current IP of the oxygen pump element 26 also decreases. Since the limiter reference voltage VL is set slightly higher than the output voltage Vs- at the target air-fuel ratio, when the output voltage Vs= reaches the limiter reference voltage VL, it indicates that the blackening phenomenon has approached the region where the blackning phenomenon occurs. When Vs->VL, the richer the air-fuel ratio is, the higher the output voltage of the operational amplifier 45 becomes, reducing the pump current IP and preventing the blackning phenomenon from occurring.

In the air-fuel ratio control circuit 21, the absolute pressure Pa^ in the intake manifold 4 and the cooling water temperature Tw are input from the Δ/D converter 73.
sIntake temperature TA, oxygen concentration in exhaust gas, and vehicle speed V+-
Alternatively, information indicating the engine speed Ne is supplied from the counter 75, and on/off information of the clutch switch 23 and Nicotral switch 24 is supplied from the digital input camosulator 77 to the CPU 80 via the input/output bus 83. be done. The CPU 80 is configured to generate an internal interrupt signal every 1 duty period TSQL (for example, every 100 m5ec), and in response to this interrupt signal, the CPU 80 generates an internal interrupt signal for duty control of the intake secondary air supply as described later. Perform the action.

Next, the operation of the intake secondary air supply system according to the present invention will be explained with reference to the operation flowcharts of the CPU 80 shown in FIGS. 5 to 7.

In cpuso, first, a quantity valve drive stop command is issued to the drive circuit 79 to close the electromagnetic on-off valve 14 every time an interrupt signal is generated (step 91). This is CP
This is to prevent malfunction of the electromagnetic on-off valve 14 during the calculation operation of U80. Next, the closing time TA of the electromagnetic on-off valve 171
F is made equal to 1 duty cycle TsOL (step 92), and the opening time TOUT of the electromagnetic on-off valve 14 is
The A/F rubon shown in FIG. 5 is executed to calculate (step 93).

In the A/1 Nil-Chin, first, the operating state of the vehicle (including the operating state of the engine) is determined by air-fuel ratio feedback (F/B
) It is determined whether the control conditions are satisfied (step 931). If it is determined that the air-fuel ratio feedback control conditions are not satisfied, the valve opening time TOUT is set to “0”.
(Step 932). Since there is a possibility that a blackning phenomenon may occur, the content of the IP value command data supplied to the programmable voltage generation circuit 42 to stop the supply of pump current is changed to 'Ip=O', for example, when a 4-bit digital signal is set. If so, it is changed to "o o o o" (step 933). This Ip value command data causes the reference voltage V r + to become 0 (V), and the output level of the operational amplifier 44 becomes a low level, so the transistor 4
5 is turned off, and the electrode plate 30.3 of the oxygen pump element 26
Pump current stops flowing within 1 hour. On the other hand, if it is determined that the air-fuel ratio feedback control conditions are satisfied, the content of the Ip value command data supplied to the programmable voltage generation circuit 42 is changed to a predetermined oxygen concentration detection value (Iρ≠
0° (step 934).

Then, the secondary air supply for one deco-tied period Tso+-, that is, the standard j"i-ti ratio (
period)D[3ASE is set (step 935).

As shown in FIG. 7, the standard duty ratio DsASE determined from the intake manifold internal absolute pressure PBA and the engine speed Ne is prewritten in the ROM 41 as a r)sASE data map, so the CPU 80
reads the absolute pressure PBA and engine speed Ne, and calculates the standard duty ratio D e AS corresponding to the 8 read values.
Search for E from the DBASE data map. Next, C
It is determined whether the word count time of the internal time counter A (not shown) of the PU 80 has elapsed for a predetermined time Δt1 (
step 936). The predetermined time tI corresponds to the response delay time from when the intake secondary air is supplied until the result is detected by the oxygen concentration sensor 19 as a change in the oxygen concentration in the exhaust gas. When the predetermined time Δt1 has elapsed from the time when the time counter A was reset and familiarization started, the time counter A is reset and counting starts from the initial value (step 937). That is, after the time counter A starts counting from the initial value by executing step 937, it is determined in step 936 whether the predetermined time Δt1 has elapsed. When the time counter Δ starts counting the predetermined time Δt1, a target air-fuel ratio leaner than the stoichiometric air-fuel ratio is set (step 938). To set this target air-fuel ratio, the ROM 81 stores a reference level l ref h (as an A/F data map D8ASE: The data map is stored in advance separately from the F-data map.Therefore, cpuso searches from the li level Iref@A/F data map according to the absolute pressure PBA and the engine speed Ne.Then, the M element is searched from the information on the oxygen concentration. It is determined whether the output level 102 of one concentration sensor +j is greater than the reference level 1 ref determined in step 938 (step 939).In other words, the air-fuel ratio of the air-fuel mixture supplied to the engine 5 is equal to the target air-fuel ratio. It is determined whether it is leaner or not.Lo2>Lref
If so, the air-fuel ratio is leaner than the target air-fuel ratio, so the nose reduction value IL is calculated (step 9310). Subtraction value IL
is obtained by multiplying a constant by +, engine speed Ne, and absolute pressure PBA (K+ - Ne '' PBA), and depends on the intake air amount of the engine 5. After calculating the subtraction value IL. , the correction value 10LJT that has already been calculated by executing this A/F routine is read out from the memory location al of the RAM 82, and the subtraction value IL is subtracted from the read correction value 10LJT to create the new calculated value. The correction value oUT is set as the corrected value oUT and is stored in the storage location al of the RAM 82 (step 9311).On the other hand, if LO2≦l ref in step 939, the air-fuel ratio is richer than the target air-fuel ratio, so the additional value IR is
is calculated (step 9312). The additional value IR is a constant of 2 (≠Kl), engine speed Ne and absolute pressure P.
It is obtained by multiplying BA with each other (K2 .Ne-PBA), and is made to depend on the intake air amount of the engine 5. (After calculating the single value IR, the correction value 10LJT, which has already been calculated by executing the A/F routine, is read from the storage location at of the RAM 82, and the addition value IR is added to the read correction value 10UT. The calculated value is set as a new correction fa I o LJ T and is stored in RAM8.
2 memory location a1 (step 9313)
. In this way, the correction value 1OUT is set to step 9311 or 93.
13, the correction value l0UT and the M quasi-duty ratio DBA set in step 935
SE and the addition σ result is the valve opening time T o (
JT (step 9314).

Note that if it is determined in step 936 that the predetermined time ΔtI has not elapsed since the time counter A was reset to 1 to 31 from the initial value in step 937, step 9314 is immediately executed. , in this case, the correction value 1o obtained from the previous execution of the Δ, /F routine from the memory location a1 of the RAM 82
uv is read out and set as the current correction value l0UT.

When the execution of the Δ/F routine is completed, the valve closing time TAF is determined by subtracting the valve opening time Tout from one duty cycle TsOL (step 94). next,
A value corresponding to the valve closing time TAF is set in the internal time counter B (not shown) of the CPtJ 80, and down counting of the time counter B is started (step 95). Then, it is determined whether or not the counted value of time counter B has reached O'' (step 96), and if the counted value of time counter B has reached 0'°, the seven drive circuits are driven to open the valves. A command is generated (step 97).

In response to this valve opening drive command, the drive circuit 79
During this period, the valve driving state is then changed to step 91.
will continue until executed. If the lesson value of time counter B does not reach 110 I+ in step 96, step 96 is repeatedly executed.

Therefore, in the intake secondary air supply device according to the present invention, the electromagnetic on-off valve 14 is immediately closed in response to the generation of the interrupt signal INT, as shown in FIG. supply will be stopped. Also, the closing time TA of the electromagnetic on-off valve 14, which is turned on in one duty cycle TSOL.
F is calculated, and the valve closing time TAF is calculated from the time of occurrence of the interrupt signal.
When the period has elapsed, the electromagnetic on-off valve 14 is opened and the engine 5 is opened.
Intake secondary air is supplied to the intake secondary air through an intake secondary air supply passage 13. Because this operation is repeated, the intake secondary air is duty-controlled. By controlling the intake secondary air in this manner, the air-fuel ratio of the air-fuel mixture supplied to the engine 5 is controlled to the target air-fuel ratio. Furthermore, the responsiveness to the intake secondary air supply command and the accuracy of air-fuel ratio control can be improved. Further, by determining the reference duty ratio D8ASE according to the operating state of the engine, it is possible to compensate for the control tloi based on changes in the operating state over time.

Next, the determination of sufficiency of the air-fuel ratio feedback control condition in step J3 in step 931 will be explained according to the sufficiency determination routine shown in FIG. In this sufficiency determination routine, first, it is determined whether the clutch switch 23 is on or not (step 101). If the clutch switch 23 is on, the clutch is released, so it is assumed that the gear is in a gear change state, and the valve closing time TouT is set to "0" to stop the air-fuel ratio feedback control (step 932). If the clutch switch 23 is off, the clutch is engaged, so it is determined whether the neutral switch 24 is on (step 102). Neutral switch 24
If it is on, the shift lever for shifting is in the neutral position, so it is determined that the gear is in the shifting state, and step 932 is executed. If the neutral switch 24 is off, the gear shift lever of the transmission is in any of the first to fifth speed positions, so it is determined whether the oxygen concentration sensor 19 has been activated (step 103).

If the oxygen concentration sensor 19 is not activated because its temperature is low, step 932 is executed. If the oxygen concentration sensor 19 has already been activated, it is determined whether the intake air temperature TA is equal to or higher than a predetermined temperature T1 (for example, 15°C) (step 104), and if rA≦T1, the intake air temperature is low. Therefore, step 932 is executed. T8>T+
Then, the vehicle speed Vz is the predetermined speed V+ (for example, 8KJ
n/h) or more is determined (step 10
5). If V+-+≦v1, the vehicle speed is low, so step 932 is executed to stop the air-fuel feedback control. If VH>V+, it is determined whether the cooling water temperature Tw is equal to or higher than a predetermined temperature T2 (for example, 70°C) (step 106), and since Tw≦Ty and j are low cooling water temperatures, step 932 is executed. be done. When TV>T2, the engine speed Ne is the first predetermined speed N+
(For example, 650r, I), 1) or less is determined (step 107). If Ne<N+, since the engine speed is low, step 932 is executed and the supply of intake secondary air is will be stopped. If Ne is N1, it is determined whether the engine rotational speed is equal to or higher than a second predetermined rotational speed N2 (for example, 250 Or, p, m2) which is larger than the first predetermined rotational speed N1 (step 108), and Ne> N
When it is 2, it is high 1st engine rotation speed, so step 93
2 is executed. When Ne≦N2, it is determined whether the absolute pressure P8A in the intake manifold 4 is greater than a first predetermined absolute pressure PBAI (for example, 210 my HCJ) (step 109). If PDA≦Pa A I, the load on the engine 5 is low, so step 932 is executed to stop the air-fuel ratio feedback control, and P
8A>PBAI, the second predetermined absolute pressure PaA2 (
For example, it is determined whether or not it is greater than (460m1-IQ) (step 110). If PBA>PBA2,
Since the load on the engine 5 is high, step 932 is executed. If PEA≦PeA2, power valve 1
2, it is determined whether or not the amount of fuel is being increased (step 11).
1). The fuel increase operation executes other fuel increase routines by CPU8.
0 is executed, and when the fuel increase is determined when the fuel increase R routine is executed, the CPU 80 issues a valve opening drive command to the drive circuit 78, so the power valve 12 opens and the fuel increases. It is supposed to be done.

When fuel is increased, the fuel increase flag Ff in the CPU 80 is set to “
1" is set, so fuel increase m from the state of flag Ff
It is determined whether it is inside or not. If F, f=1, the fuel is being increased, so step 932 is executed to stop the air-fuel ratio feedback control. If Ff=O, the fuel is not being increased, so it is determined whether the gear shift lever of the transmission is in one of the third to fifth gears (
Step 112). In this determination, the gear shift position is determined from the ratio between the engine speed Ne and the vehicle speed VH. If it is determined that the speed change lever is in either the first or second speed, this is the low speed shift position, so step 932 is executed. If it is determined that the gear shift lever is in any one of the third to fifth gears, the change speed of the high-speed VH per unit time is such that the magnitude of the VH is equal to or higher than the predetermined speed V2 (for example, 2KJR/h). It is determined whether or not (step 113).

If IΔVh(l>V2, step 932 is performed to stop the air-fuel ratio feedback control as a transient operation state
is executed. If 1Δ■)41≦■2, it is assumed that the change in vehicle speed VH is small and the vehicle is in a steady operating state, and the air-fuel ratio feedback control conditions are satisfied, and step 934 is executed.

Duty cycle Ts in which steps 932 and 933 were executed because the air-fuel ratio feedback control conditions were not satisfied
In the OL, the valve opening time TOUT is set to 0'', so the electromagnetic on-off valve 14 is opened and the supply of air is stopped at 2 hours of intake.Therefore, the air-fuel ratio of the supplied air-fuel mixture is enriched. Furthermore, since the current supply to the oxygen pump element 26 is stopped, the occurrence of blackening phenomenon can be avoided.

As described above, in the air-fuel ratio control 11 device of the present invention,
When the engine is in a predetermined operating state, determination of the air-fuel ratio is stopped according to the voltage generated between the electrodes of the battery element or the current flowing between the electrodes of the oxygen pump element, and the current supply to the oxygen pump element is stopped. be done. In other words, the air-fuel ratio feedback control is stopped and the oven loop control il'
The blackening phenomenon occurs by stopping the current supply to the M element pump element when the operating state is such that an increase in fuel is required, or a transient operating state where the rate of change in operating parameters is large. can be avoided, and rapid deterioration of the oxygen pump element can be prevented. In particular, in the case of an air-fuel ratio control device using an intake secondary air supply method, the air-fuel ratio of the supplied air-fuel mixture varies greatly due to variations in the base air-fuel ratio of the carburetor, so if the present invention is applied,
This makes it possible to reliably prevent the occurrence of the blackening phenomenon.

[Brief explanation of drawings]

FIG. 1 is a dimensional diagram showing the oxygen concentration-pump current characteristics and the blackening phenomenon occurrence area, FIG. FIG. 4 is a block diagram showing the configuration of the air-fuel ratio control circuit in the device of FIG. 2, and FIGS. 5 and 6 are diagrams showing the configuration of the oxygen concentration sensor.
9 and 9 are flowcharts showing the operation of the CPU, FIG. 7 is a diagram showing the data map written in the ROM, and FIG. 8 is a diagram showing the operation timing of the apparatus of FIG. 2. Explanation of symbols of main parts 2... Air cleaner dog 3... Carburetor 4... Intake manifold 6... Throttle valve 7... Venturi 12...Power valve 13...Intake secondary air supply passage 14...
・Solenoid on-off valve 15... Absolute pressure sensor 16... Crank angle sensor 17... Cooling water wetness sensor 19... Oxygen concentration sensor 20... ... Exhaust manifold 26 ... Oxygen pump element 27 ... Battery element 28 ... Gap section 29 ... Spacer 30 to 33 ... Electrode Applicant: Honda Motor Co., Ltd. Agent: Motohiko Fujimura, Patent Attorney Figure 1 Menglycium concentration Figure 2 Figure 7 r, p, m. Figure 8 Time

Claims (2)

[Claims] (1) A pair of oxygen ion conductive solid electrolyte materials disposed in the exhaust gas of an internal combustion engine, a pair of electrodes are formed on each of the solid electrolyte materials, and the pair of solid electrolyte materials are arranged in a predetermined gap. between the electrodes of the oxygen pump element and oxygen concentration detection means, which are arranged so as to face each other with one of the solid electrolyte materials functioning as an oxygen pump element and the other as a battery element for measuring acid concentration ratio; a current supply means for supplying a current; a determination means for determining an air-fuel ratio of the air-fuel mixture supplied to the engine according to a voltage generated between the electrodes of the battery element or a current value flowing between the electrodes of the oxygen pump element; and an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the supplied air-fuel mixture according to the determination result of the determining means, and when the engine is in a predetermined operating state, the determining means stops determining the air-fuel ratio, and the oxygen pump stops determining the air-fuel ratio. An air-fuel ratio control device characterized by stopping current supply to an element. (2) The air-fuel ratio control device according to claim 1, wherein the predetermined operating state is a fuel increase operating state, a decelerating operating state, or an accelerating operating state.