JPS62288341A - Air-fuel ratio control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the hunting of an air-fuel ratio and improve the drivability, by fixing an air-fuel ratio correction value at a predetermined value when the number of times of inversion of a detection value from an O2 sensor exceeds a predetermined value at low load operation, and stopping the air-fuel ratio control when the detection value is in an inactive state. CONSTITUTION:Detection values from an intake absolute pressure sensor 10, a crank angle sensor 11, a cooling water temperature sensor 12, an O2 sensor 14 and a throttle valve opening sensor 17 are input to a control circuit 20. Then, an opening degree of a linear type solenoid valve 9 provided in a secondary intake air supply passage is controlled so that an air-fuel ratio becomes a target value according to an operational condition. When the control circuit 20 determines that the operational condition is an idling according to the throttle valve opening and the intake absolute pressure, it counts the number of times that the output from the O2 sensor 14 crosses a reference value. When the number of times counted becomes a predetermined number, an air-fuel ratio correction value is fixed at an update value for controlling the air-fuel ratio to a theoretical air-fuel ratio. When the output becomes an inactive state by a resistance of the O2 sensor 14, the airfuel ratio control is stopped.

Description

[Detailed description of the invention] 3. Detailed description of the invention Flame Hill 1 The present invention relates to an air-fuel ratio control method for an internal combustion engine.

In order to purify the exhaust gas of internal combustion engines and improve fuel efficiency, the oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor, and the air-fuel mixture supplied to the engine is adjusted according to the output level of this oxygen concentration sensor. An air-fuel ratio control device that performs feedback control of an air-fuel ratio is known.

As this air-fuel ratio control device, a solenoid valve is provided in the intake secondary air supply passage communicating downstream of the carburetor throttle valve, and the opening degree of the solenoid valve, that is, the intake secondary air supply range, is controlled according to the output level of the oxygen am sensor. There are air-fuel ratio control devices using intake secondary air supply force for feedback control (for example, the
-3533).

In such conventional air-fuel ratio control devices, the air-fuel ratio of the supplied air-fuel mixture is lean or rich with respect to the target air-fuel ratio based on the output level of an exhaust component concentration sensor that detects the concentration of exhaust components such as oxygen concentration in exhaust gas. Normally, it is determined which one is, and a proportional amount and an integral layer are set according to the determination result to perform PI (proportional integral) control on the intake secondary air supply level or the fuel supply amount.

By the way, when the engine is operating at a low load, especially when the engine is idling, the exhaust gas concentration decreases and the exhaust component concentration sensor is cooled, so even if the concentration remains the same, the output level may decrease and become inactive. Therefore, immediately after accelerating from idling and starting air-fuel ratio feedback control, the exhaust component concentration sensor is not activated, making it impossible to accurately control the air-fuel ratio to the target air-fuel ratio, resulting in an increase in unburned harmful components in the exhaust. There was a problem that there were cases.

m and 1 Therefore, an object of the present invention is to provide an air-fuel ratio control method that can prevent an increase in unburned harmful components in the exhaust immediately after switching to operation without air-fuel ratio feedback control during low-load operation. be.

The air-fuel ratio control method of the present invention detects that the number of times the detected exhaust component concentration has reversed from small to large or from large to small with respect to the l target value has reached a predetermined number or more in a low-load operating state of the engine. When detected, the air-fuel ratio correction value is fixed at a predetermined value, and when the inactive state of the exhaust component concentration sensor is detected from the detected exhaust component concentration value, the air-fuel ratio control is stopped until the active state of the exhaust component m eaves sensor is detected. It is characterized by

Real-JLJI Embodiments of the present invention will be described below with reference to the drawings.

In the intake secondary air supply system for an on-vehicle internal combustion engine, which is an embodiment of the present invention shown in FIG. supplied to vaporizer 3
A throttle valve 6 is provided, and a venturi 7 is formed upstream of the throttle valve 6.

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 8.

A linear solenoid valve 9 is provided in the intake secondary air supply and supply passage 8 . The opening degree of the solenoid valve 9 changes in proportion to the current value supplied to the solenoid 9a.

On the other hand, 10 is an absolute pressure sensor installed in the intake manifold 4 and generates an output at a level corresponding to the absolute pressure inside the intake manifold 4, and 11 generates a pulse in accordance with the rotation of the crankshaft (not shown) of the engine 5. The crank angle sensor 12 is a cold 7JI water sensor that generates an output level according to the cooling water temperature of the engine 5! = Nsa, 14 is engine 5
W! is installed in the exhaust manifold 15 of the exhaust gas and outputs an output according to the M-wire concentration in the exhaust gas. It is an i elementary concentration sensor. Exhaust manifold 1 downstream from the location of oxygen concentration sensor 14
5 is provided with a catalytic converter 33 to promote the reduction of harmful components in exhaust gas.

Solenoid valve 9, absolute pressure sensor IJ-10, crank angle sensor 1
1. The water temperature sensor 12 and the oxygen m1 degree sensor 14 are connected to the control circuit 20. The control circuit 20 further includes a vehicle speed sensor 16 that generates an output level that corresponds to the speed of the vehicle, and a throttle valve opening sensor 17 that is composed of a potentiometer and generates an output level that corresponds to the opening degree of the throttle valve 6. It is connected.

The control circuit 20 includes an absolute pressure sensor 10, as shown in FIG.
Water temperature sensor 12, M element concentration sensor 14, vehicle speed sensor 16
and a level conversion circuit 21 that converts each output level of the throttle valve opening sensor 17, and a multi-branch converter 22 that selectively outputs one of the outputs of each sensor that has passed through the level conversion circuit 21.
, an A/D converter 23 that converts the signal output from the multiplexer 22 into a digital signal, and a waveform shaping circuit 24 that shapes the waveform of the output signal of the crank angle sensor 11.
and TD output as a pulse from the waveform shaping circuit 24.
A counter 25 that measures the generation interval of the C signal by the number of clock pulses output from a clock pulse generation circuit (not shown), a drive circuit 28 that drives the solenoid valve 9 to open, and a CPLI that performs digital calculations according to a program.
(central processing circuit) 29, a ROM 30 in which various processing programs and data are written in advance, and a RAM 31. The solenoid 9a of the electromagnetic valve 9 is connected in series with a drive transistor and a current detection resistor (both not shown) of a drive circuit 28, and a power supply voltage is supplied across the series circuit. Multiplexer 22, A/D converter 23, counter 25, drive circuit 28, CPU 29, RO
M30 and RAM31 are connected to each other by an input/output bus 32.

In such a configuration, information on the absolute pressure in the intake manifold 4, cold tJJ water temperature, oxygen concentration in exhaust gas, vehicle speed, and throttle valve opening is selectively transmitted from the A/D converter 23, and information on the engine is transmitted from the counter 25. Information representing the number of rotations is sent to CPU2
9 via the input/output bus 32. CPU2
9 is a predetermined circle 11”r+ (for example, 50m5e) as described below.
c) An internal interrupt signal is generated every time, and in response to the interrupt signal, the supply current value DOLI7 to the solenoid 9a of the solenoid valve 9 is calculated as data, and the calculated supply current value DOUT is driven. Supplied to circuit 28. Drive circuit 2
8, the current value flowing through the solenoid 9a is the supply current 1 direct DO
A leap loop control is performed on the value of the current flowing through the slider 9a so that the current value becomes LJ.

Next, the steps of the air-fuel ratio control method according to the present invention will be described in the third step.
A detailed explanation will be given according to the operation flow diagram of the CPU 29 shown in the figure.

The CPtJ 29 first determines whether the inactivation flag Fs is equal to 1 each time an interrupt signal is generated (step 51).

When Fs = 1, it means that the oxygen concentration sensor 14 is in an inactive state, so the oxygen concentration 1-02 detected by the oxygen concentration sensor 14 is read and the oxygen concentration LO2 is set to a predetermined value L1 (for example, the oxygen concentration sensor 14 is in an inactive state. 14 (output voltage level of 0.7 V) (step 52). If LO2≦11, it is assumed that the activation of the oxygen concentration sensor 14 has not been completed, and the solenoid valve 9 is closed and the supply current value DOLJT is set equal to 0 to stop the air-fuel ratio feedback control (step 53).

Note that when the engine is started, the inactivity flag Fs is set to 1, which indicates that the oxygen concentration sensor 14 is in an inactive state.

If Lo2>L+, it is assumed that the activation of the mlst degree sensor 14 has been completed, and the inactivation flag Fs is set equal to O (step 54), and the operating state of the vehicle (including the operating state of the engine) is changed to the air-fuel ratio feedback (F /B) Determine whether the control conditions are satisfied (step 55). Further, when Fs -0 in step 51, it is determined that the oxygen concentration sensor 14 is already in the active state, so the determination in step 55 is immediately executed. This determination is made based on the intake manifold absolute pressure, cooling water temperature, vehicle speed, throttle valve opening, and engine speed. For example, it is determined that the air-fuel ratio feedback control conditions are not satisfied at low vehicle speeds and low cooling water temperatures. Here, if it is determined that the air-fuel ratio feedback control conditions are not satisfied, step 53 is executed to close the solenoid valve 9 and make the supply current value Douv equal to O in order to stop the air-fuel ratio feedback control.

On the other hand, if it is determined that the air-fuel ratio feedback control conditions are satisfied, the reference current value Da of the current value supplied to the solenoid valve 9 is
ASE is set (step 56). ROM30
As shown in Figure 4, the absolute pressure inside the intake manifold PB
Reference current value Da determined from A and engine speed Ne
Since ASE has been written in advance as a DeAse data map, the CPU 29 reads the absolute pressure PsA and the engine speed Ne, and searches the DBASε data map for the reference current value DBASE corresponding to each read value. Next, it is determined whether the oxygen concentration 61 degrees LO2 detected by the gin degree sensor 14 is smaller than the target value LREr: corresponding to the target air-fuel ratio (step 57).

If LO2<LREF, the air-fuel ratio is lean, so it is determined whether the air-fuel ratio flag FAF is equal to 0 (
Step 58). If FAF=O, it is assumed that the air-fuel ratio continues to be in a lean state and the state of the air-fuel ratio flag FAF is maintained, and if FAF is 1, it is assumed that the air-fuel ratio has reversed from rich to lean. and set the air-fuel ratio flag FAF to 0.
(step 59). If L2≧REF, the air-fuel ratio is rich, so the air-fuel ratio flag FAF
is equal to 1 (step 60). F.A.
; If = 1, it is assumed that the air-fuel ratio continues to be in a rich state, and the air-fuel ratio flag is maintained at "A" and FA
If =O, it is assumed that the air-fuel ratio has reversed from lean to ridge, and the air-fuel ratio flag FAF is set equal to 1 (step 61). When the air-fuel ratio is reversed in this way, it is determined whether or not the engine is in an idling state (step 62). The idle operating state is determined, for example, from the throttle valve opening θth, or from the intake manifold self-supply pressure PBA, and the throttle valve opening θ[h
is less than the predetermined opening θ1, or the intake -? When the absolute pressure PBA in the second hold is less than the predetermined pressure P1, it is determined that the engine is idling. If it is not in the idle operating state, the variable WIN is reset by making it equal to an integer N+ (for example, 3) (step 63), and it is determined whether the IQ elementary concentration LO2 is smaller than the target value LREF corresponding to the target air-fuel ratio. It is determined (step 64).

If LO2<LREF, the air-fuel ratio is leaner than the target air-fuel ratio, so a predetermined proportion ff1P is subtracted from the air-fuel ratio feedback correction coefficient KO2 forming the air-fuel ratio correction value, and the calculated value is newly set as the correction coefficient ``KO2''. step 65),
, if LO2≧LP5F, the air-fuel ratio is richer than the target air-fuel ratio, so a predetermined proportional mp is added to the air-fuel ratio feedback correction coefficient KO2, and the calculated value is set as a new correction coefficient K.
O2 (step 67). After outputting the correction coefficient KO2 in step 65 or 67, the reference current value 0BAsE set in step 56 is multiplied by the correction coefficient 02, and the multiplication result is set as the supply current value DOU (step 68), supply current 1iflDoU1 is output to the drive circuit 28 (step 69).

On the other hand, if it is in an idling state, 1 is subtracted from the variable N and the output value of n is set as a new variable N (step 70).
, determine whether the calculated variable N is equal to O (
Step 71). If N≠O, the predetermined time has not passed since the start of idling and a stable idling state has not been reached, so steps 64 to 69 are executed to reduce the supply current value DOUT in order to perform air-fuel ratio feedback control. is calculated and output to the drive circuit 28. If N=O, a stable idling state has been reached in terms of time, and if air-fuel ratio feedback control is performed, the engine speed will fluctuate and become unstable, so the correction coefficient KO2 should be set to a predetermined value. (For example, if the air-fuel ratio is 1
At step 72), the oxygen concentration 102 detected by the M elementary concentration sensor 14 is fixed at a predetermined value L2 (for example, the output voltage level of the oxygen concentration sensor 14). 0.3V) (step 73). L02≧L2
At this time, the oxygen concentration sensor 14 is assumed not to be in an inactive state during idling operation, and step 68.6 is performed to control the air-fuel ratio of the oven loop using 02=+.
By executing step 9, the supply current value DOUT is calculated and outputted to the drive circuit 28. When LO2<12, the oxygen concentration sensor 14 is assumed to be inactive during idling, and the inactive flag Fs is set to 1 in step 7/l.
),? The supply current value DOUT is made equal to 0 in order to close the ft1l valve 9 and stop the air-fuel ratio feedback control (step 53).

When it is determined in steps 58 to 60 that the air-fuel ratio is not inverted, it is determined whether the oxygen concentration LO2 is smaller than the target value LREF corresponding to the target air-fuel ratio (step 75). If LO2<LREF, the air-fuel ratio is higher than the target air-fuel ratio, so the air-fuel ratio feedback correction coefficient K.

A predetermined integral ♀■ is subtracted from 2 and the calculated value is newly set as a correction coefficient KO2 (step 76). If LO2≧LREF, add a predetermined product numerator ftl from the air-fuel ratio feedback correction coefficient KO2 and use the calculated value as a new correction coefficient Koz.
(Step 77).

After calculating the correction coefficient KO2 in step 76 or 77, the supply current value DOLI is adjusted by executing steps 68 and 69.
T is calculated and output to the drive circuit 28.

The drive circuit 28 detects the current value flowing through the solenoid 9a of the solenoid valve 9 using a current detection resistor, compares the detected current value with the supplied current value DOU, and turns the drive transistor on and off according to the comparison result. Solenoid 9a
supply current to.

Therefore, a current having the supply current value DOLIT flows through the solenoid 9a, and an amount of secondary intake air proportional to the current value flowing through the solenoid 9a is supplied into the intake manifold 4. Further, in the case of the supply current value DouT/fiO, the solenoid valve 9 is closed and the supply of intake secondary air is stopped.

In the apparatus J3 to which the air-fuel ratio control method of the present invention is applied, if the air-fuel ratio detected from the oxygen concentration is reversed with respect to the target air-fuel ratio and is in an idling operating state, the apparatus is in an idling operating state for a predetermined period of time after entering an idling operating state. If no elapsed time, P
A correction coefficient KO2 is determined by I (differential-integral) control, and air-fuel ratio feedback control is performed. When a predetermined period of time has elapsed since the idling operation, the inactive state of the oxygen concentration sensor 14 is determined from the output of the oxygen concentration sensor 14, and if the oxygen concentration sensor 14 is not in an inactive state, the correction coefficient is set to 02 and fixed to a predetermined value of 1. Open loop emptying is performed, and if it is in an inactive state, the inactive flag FS is set to 1 and the air-fuel ratio control is about to stop.

As a result, if Fs = 1 when transitioning from idling to an operating state that satisfies the air-fuel ratio feedback control conditions in J3 in step 55, air-fuel ratio control will be stopped until activation of the oxygen concentration sensor is completed. be.

Furthermore, if the oxygen concentration sensor 14 is in an active state by fixing the correction coefficient KO2 so that the air-fuel ratio of the a-air gas supplied to the engine is 14.7, the oxygen concentration Lo2 will be increased by 1!7 by the oxygen concentration sensor 14. is never smaller than [2, so the inactive state can be determined. When air-fuel ratio control is stopped, valve 9 is closed and the air-fuel ratio of the supplied mixture becomes rich, so if oxygen concentration sensor 14 is active, oxygen concentration L obtained by oxygen m degree sensor 14
Since o2 is larger than Ll, it is possible to determine the activity.

In the above-described embodiments of the present invention, an air-fuel ratio control device equipped with a linear solenoid valve has been described. Valve time TauT (=standard valve opening time Ts A
SEX correction coefficient KO2) is calculated and its valve opening time T
The present invention can also be applied to an air-fuel ratio control device that opens an electromagnetic on-off valve only at OUT.

In addition, in the embodiments of the present invention described above, the air-fuel ratio control method of the present invention was applied to an air-fuel ratio control device using an intake secondary air supply method, but a method in which fuel is injected and supplied by an injector and the injection hole is controlled is used. The present invention can also be applied to this device.

As shown in 几 12 and 1 ri, in the air-fuel ratio control method of the present invention, the number of times the detected exhaust component concentration value reverses from small to large or from large to small with respect to the target value in the low-load operating state of the engine When it is detected that the air-fuel ratio has reached a predetermined number of times or more, the air-fuel ratio correction value is fixed at a predetermined value and the air-fuel ratio is controlled by an oven loop, which prevents hunting of the air-fuel ratio and improves performance during idle operation, etc. The state can be stabilized. In addition, after fixing the air-fuel ratio correction value to a predetermined value, if the inactive state of the exhaust component concentration sensor is detected from the detected exhaust component concentration value, the other air-fuel ratios will be changed until activation of the exhaust component concentration sensor is completed. Since air-fuel ratio control is not started even if the feedback control conditions are satisfied, it is possible to prevent the increase in unburned harmful components in the exhaust gas as in the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an air-fuel ratio control device to which the air-fuel ratio control method of the present invention is applied, FIG. 2 is a block diagram showing a specific configuration of a control circuit in the device in FIG. 1, and FIG. 3 is a CPU FIG. 4 is a flowchart showing the operation of ROM1. : A diagram showing a written data map. Explanation of symbols of main parts 2... Air cleaner 3... Carburetor 4... Intake manifold 6... Throttle valve 7... Venturi 8 ......Intake secondary air supply passage 9...Linear type solenoid valve 10...Absolute pressure hinge 111...Crank angle sensor 12... ... Cooling water temperature sensor 14 ... Oxygen concentration sensor 15 ... Exhaust manifold 17 ... Throttle valve opening sensor 33 ... Catalytic converter applicant Honda Motor Co., Ltd. Agent Co., Ltd. Patent Attorney Motohiko Fujimura Figure 1

Claims (2)

[Claims] (1) Compare the exhaust component concentration detection value detected by the exhaust component concentration sensor installed in the exhaust system of the internal combustion engine with the target value, set the air-fuel ratio correction value according to the comparison result, and supply it to the engine. The air-fuel ratio control method performs feedback control of the air-fuel ratio of the air-fuel mixture according to the set air-fuel ratio correction value, wherein the detected exhaust component concentration value is smaller than the target value in a low-load operating state of the engine. When it is detected that the number of times the air-fuel ratio has changed from large to large or from large to small has reached a predetermined number or more, the air-fuel ratio correction value is fixed to a predetermined value, and the error of the exhaust component concentration sensor is determined based on the detected exhaust component concentration value. An air-fuel ratio control method characterized in that when an active state is detected, air-fuel ratio control is stopped until an active state of the exhaust component concentration sensor is detected. (2) The air-fuel ratio control method according to claim 1, wherein when the detected exhaust component concentration value is smaller than a predetermined value, it is determined that the exhaust component concentration sensor is in an inactive state.