JPS62288338A - Air-fuel ratio control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To correct a slippage of a base air-fuel ratio, by correcting a reference value for air-fuel ratio control as set according to an engine load with a deviation between an output value of an O2 sensor and a target value, and correcting the target value when a correction value indicative of an error in the reference value is not less than a predetermined value. CONSTITUTION:A control circuit 20 reads a reference value for air-fuel ratio control from a data map according to an engine speed from a crank angle sensor 11 and an intake absolute pressure from an intake absolute pressure sensor 10 both relating to an engine load. When it is determined that air-fuel ratio feedback control conditions are satisfied from the intake absolute pressure, cooling water temperature, vehicle speed and engine speed, an integral term and a proportional term for feedback controlling a secondary air control valve 9 according to the engine speed and intake absolute pressure are calculated. Further, a present correction value of the reference value is calculated from a previous correction value and the integral term or the proportional term. When the present correction value becomes a predetermined value or more, or becomes a predetermined value or less, it is determined that a slippage of a base air-fuel ratio in a carburetor 3 has occurred, and a target value for the feedback control is therefore corrected.

Description

[Detailed description of the invention] 3. Detailed description of the invention flame hill light 1 The field relates to an air-fuel ratio control method for internal combustion engines.

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 ratio of the mixture supplied to the engine is set according to the output level of the oxygen concentration sensor. Air-fuel ratio control devices that perform feedback control on the air-fuel ratio are known (for example,
-3533 publication).

In such an air-fuel ratio control device, a reference value for air-fuel ratio control is set according to multiple engine operating parameters related to engine load, and the output value of an exhaust component concentration sensor such as an oxygen concentration sensor and a target air-fuel ratio are determined at predetermined intervals. The output value is determined by comparing the target value corresponding to the fuel ratio and correcting the reference value according to the comparison result, and the opening degree of the air-fuel ratio adjustment valve N13 is controlled according to the output value. It has become.

By the way, it is common for the base air-fuel ratio of the carburetor to deviate from a predetermined value due to aging or deterioration of the carburetor, causing the set reference value to no longer correspond to the target air-fuel ratio and resulting in an error. be.

Therefore, if the error in the reference value becomes larger than a predetermined value, it becomes impossible to control the air-fuel ratio of the air-fuel mixture supplied to the engine to the target air-fuel ratio with high precision using air-fuel ratio feedback control, and good exhaust purification performance becomes impossible. There was a problem that 19-year-olds could no longer be used.

1 Group 5 II Therefore, an object of the present invention is to provide an air-fuel ratio control method that can maintain good exhaust purification performance by 1 even if the error in the reference value becomes greater than a predetermined value.

The air-fuel ratio control method of the present invention is characterized in that a correction field representing an error in a reference value is calculated, and a target value to be compared with an output value of an exhaust component concentration sensor is corrected in accordance with the magnitude of the calculated correction value. .

Friend-Ei-1 Embodiments of the present invention will be described below with reference to the drawings.

In the air-fuel ratio control device of the intake secondary air supply system for an on-vehicle internal combustion engine to which the air-fuel ratio control method of the present invention is applied, as shown in FIG. It is supplied to the engine 5 via the intake manifold 4.

The carburetor 3 is provided with a throttle valve 6, 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.

Is there a linear type in the intake secondary air supply passage 8? A jf magnetic valve 9 is provided. ? The opening degree of the 1fla 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. 12 is a cooling water temperature sensor that generates an output at a level corresponding to the cooling water temperature of the engine 5; 14 is an oxygen sensor installed in the exhaust manifold 15 of the engine 5 and generates an output according to the axe degree in the exhaust gas. It is a concentration sensor. A catalytic converter 33 is provided in the exhaust manifold 15 downstream of the oxygen concentration sensor 14 in order to promote reduction of harmful components in the exhaust gas. Linear type lll1
The magnetic valve 9, absolute pressure sensor 10, crank angle sensor 11, water temperature sensor 12, and oxygen concentration sensor 14 are connected to a control circuit 20.

Further connected to the control circuit 20 are 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 comprised of a potentiometer and generates an output level that corresponds to the opening degree of the throttle valve 6. has been done.

The control circuit 20 includes an absolute pressure sensor 10, as shown in FIG.
Water temperature sensor 12, oxygen 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 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 2 that shapes the output signal of the crank angle sensor 11.
4 and T output as a pulse from the waveform shaping circuit 24.
a counter 25 that measures the generation interval of the DC signal by the number of clock pulses output from a clock pulse generation circuit (not shown); a drive circuit 28 that drives the electromagnetic valve 9;
A CPU (
It consists of a 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 to the drive circuit 28.
The circuit is connected in series to a drive transistor and a current detection resistor (both not shown), and a power supply voltage is supplied across the series circuit. Multiplexer 22, A/D converter 23
, counter 25, drive circuit 28, CPU 29, ROM3
0 and RAM 31 are connected to each other by an input/output bus 32.

In this configuration, the A/D converter 23 selectively transmits information on the absolute pressure in the intake manifold 4, the cooling water temperature, the oxygen concentration in the exhaust gas, the vehicle speed, and the throttle valve opening, and the counter 25 selectively transmits information on the engine rotation. The information representing the number is CPLI29
are respectively supplied via the input/output bus 32. CPU29
is a predetermined period T+ (for example, 5111SO
C), and in response to the interrupt signal, an output representing the current value supplied to the solenoid 9a of the solenoid valve 9 [Tour is calculated as data,
The calculated output value TOUT is supplied to the drive circuit 28. The drive circuit 28 performs closed loop control on the current value flowing through the solenoid 9a so that the current value flowing through the solenoid 9a becomes a value corresponding to the output value TOLJT.

Next, the operation of the air-fuel ratio control bag opening will be explained in detail according to the operation flowchart of the CPU 29 shown in figure f13.

As shown in FIG. 3, in the A/F routine, the CP tJ 29 first sets a reference value Ds AS E representing the reference current value supplied to the solenoid valve 9 every time an interrupt signal is generated (step 51). As shown in Fig. 4, the ROM30 stores the intake manifold internal absolute pressure PBA and the engine speed N113.
The reference value DaAsE /fiDa A S
Since it is written in advance as an E data map, the CP
U29 reads the absolute pressure P13A and engine speed Ne, and sets the reference value Da A S corresponding to each read value.
Search for E from the DEIASE data map. Standard value D
It is determined whether the settings of BASE and the operating state of the vehicle (including the operating state of the engine) satisfy air-fuel ratio feedback (F/B) control conditions (step 52).
). This determination is based on the absolute pressure in the intake manifold Pa A,
It is determined from the cold IJ1 water temperature TW1 vehicle speed ■ and the engine rotation speed Ne, and for example, it is assumed that the air-fuel ratio feedback control condition is not satisfied at low vehicle speed and low cooling water temperature. Here, if it is determined that the air-fuel ratio feedback control conditions are not satisfied, then the repair value is determined.

ASE is multiplied by the correction value Kref and the calculated value is output value T.
oUT (step 53), and the fifth
As shown in the figure, the correction value K ref for each region corresponding to the intake manifold internal absolute pressure Pa^ and the engine speed Ne
Since the lfi K ref data map is written, the CPU 29 searches the Krer data map for the correction value Krer corresponding to the absolute pressure PBA and the engine speed Ne, and uses it to calculate the output value TauT.

On the other hand, if it is determined that the air-fuel ratio feedback control conditions are satisfied, the internal timer counter A of CPtJ29
It is determined whether the counting time (not shown) has elapsed by a predetermined time Δt1 (step 56). The predetermined time Δt1 corresponds to a response delay time from when the intake secondary air is supplied until the result is detected by the oxygen concentration sensor 14 as a change in the oxygen concentration in the exhaust gas. When a predetermined time Δt1 has elapsed since the time counter A was reset and started counting, the time counter A is reset and starts counting from the initial value (step 57).

That is, by executing step 57, the time counter A
is the first time! After starting counting from 11111, a predetermined time Δt
It is determined in step 56 whether 1 has elapsed or not. When the time counter A starts counting the predetermined time Δt1 in this way, it is determined from the oxygen concentration information whether or not the output value LO2 of the oxygen concentration sensor 14 is a person based on the target value L ref corresponding to the target air-fuel ratio. (Step 58). That is, it is determined whether the air-fuel ratio of the air-fuel mixture supplied to the engine 5 is leaner than the target air-fuel ratio. If LO2>Lref, the air-fuel ratio is leaner than the target air-fuel ratio, so it is determined whether the air-fuel ratio flag FAF representing the determination result of the previous step 58 is 1'' (step 59). FA F =0 Then, since the previous air-fuel ratio was determined to be rich and has further reversed from rich, the proportional subtraction value PL is calculated (step 60).The subtraction value PL is a constant + (>1> and the integral subtraction described later). It is obtained by multiplying the value IL by each other (K+ ・lL). After calculating the subtracted value PL, this A/F
Correction value l0LIT already calculated by executing the routine
is the memory location a of the RAM 31.

, subtract the subtraction value PL from the read air-fuel ratio correction value 10LJT, and use the calculated value as the new correction value l0U.
T and writes it into the storage location at of the RAM 31 (step 61). If FAF=1, it was determined that the air-fuel ratio was lean last time as well, so an integral subtraction value 1 +- is calculated (step 62). The reduced east value IL is calculated by multiplying the constant by 2, the engine speed Ne and the absolute pressure PBA by 1 (K2 ・Ne
-PBA), and is dependent on the intake air position of the engine 5. After calculating the subtraction value IL, the correction value fouT already calculated by executing this A/F routine is read from the storage location a1 of the RAM 31,
Subtract the subtraction value IL from the read correction value 10LIT and set the calculated value as the new correction value ○UT and store it in RAM31.
(step 63). After calculating the correction value of 100 in step 61 or 63, the flag FAF is set to “1” to indicate that the air-fuel ratio is lean.
” is added to the reference value DBASE set in step 51, and the correction value 10LIT is set as the output value TOLIT (step 65).Meanwhile, in step 58,

If 2≦L rer, the air-fuel ratio is richer than the target air-fuel ratio, so it is determined whether the air-fuel ratio flag FAF is "0" (step 66). If it is FAF-1, it is determined that the previous air-fuel ratio was lean, and the ratio has been reversed from lean to rich, so the proportional addition value PR is calculated (step 67).

The added value PR is obtained by multiplying a constant by 3 (>1) and an integral added value IR, which will be described later, *(K3·IR). After calculating the KAKO hflPR, the correction value l0UT that has already been calculated by executing this A/F routine is
The read correction value [OUT and the added value PR are added together, and the calculated value is set as a new correction value 10UT, and the memory location ffa+ of the RAM 31 is read out from the memory location a1 of AM31.
(step 68). In step 66 F
If A F =0, it was determined that the air-fuel ratio was rich last time as well, so the integral addition value In is calculated (step 69).
. The additional value IR is obtained by multiplying the constant by 4 (≠ by 2), the engine speed Ne and the absolute pressure PBA (K4 ・Ne-P
BA), and it depends on the intake air of the engine 5. After calculating the additional value IR, A
Correction value l0U already calculated by executing /F Luzin
Read T from the storage location a1 of the RAM 31, add the added value IR to the read correction value 10UT, set the calculated value as the new correction value 10UT, and read it out from the storage location a1 of the RAM 31.
(step 70). After calculating the correction value ■0LJT in step 68 or 70, 0'' is set in the 7-lag FAF to indicate that the air-fuel ratio is rich (step 71), and the correction value K ref is calculated (step 72).Correction The value Krer is )(ref -a -I
It is calculated from the formula o uT+(1-α)·Krefn-1.

Here, α is a constant, )(ref, is the previous step 72
This is the correction value K ref obtained by executing .

The calculated correction value K ref corresponds to the intake manifold internal absolute pressure PBA and engine rotation speed Ne at this time.
It is stored in the Kre4 data map location of AM31.

The calculated correction value K rat is greater than 0.9 and 1.
Determine whether it is smaller than 1 (step 73), 0
．． If 9<Kref<1.1, immediately step 65
The output value T is obtained by executing .

Calculate UT. K ref4≦0.9, or K ref
If ≧1.1, it is assumed that the difference in the correction value Kret is large due to the deviation in the base air-fuel ratio of the carburetor, and the target value 1 ref corresponding to the target air-fuel ratio is corrected (step 74).
, and then, by executing step 65, the output value TOLJT
Calculate. For example, with the characteristics shown in FIG. 6, the target value Lref corresponding to the correction value Kref is stored in the ROM 30.
It is stored in advance as a ref data map, and K
If ref≦0.9 and Krcf≧1.1, the target value Lrer corresponding to the correction value K rat is searched from the 1rer data map. If the correction value K ref becomes 1.1 or more, it means that the base air-fuel ratio of the carburetor has shifted to the rich side, so the target value ver is reduced, and the correction value K ref
If it becomes 0.9 or less, it means that the base air-fuel ratio of the carburetor has shifted to the lean side, so the target value L ref is increased.

After calculating the output value TOLJT in step 53 or 65, the output value TOLJT is output to the drive circuit 28 (step 75).

Note that, instead of determining the target value L ref stepwise with respect to the correction value K ref as shown in FIG. 6, the target value L rcr may be determined continuously with respect to the correction value K ref. good. In addition, the RAM 31 is non-volatile, and its memory contents do not volatize even when the engine 5 stops operating.
C "Each K rat in the data map must be set to 1 before using this device.
is initialized to .

The drive circuit 28 detects the current value flowing through the solenoid 9a of the solenoid valve 9 using the I1Ii current detection resistor, compares the detected current value with the output value TOIJT, and turns on and off the drive transistor according to the comparison result to control the solenoid. A current is supplied to 9a. Therefore, the current represented by the output value TOU flows through the solenoid 9a, and the primary intake secondary air proportional to the current value flowing through the solenoid 9a of the M magnetic valve 9 is supplied into the intake manifold 4.

Note that after the time counter A is reset in step 57 and starts counting from the initial value, a predetermined time Δ
If it is determined in step 56 that 1+ has not elapsed, step 65 is immediately executed; in this case,
The correction value l0UT obtained by executing the A/F routine up to the previous time is read out.

In addition, 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 opening time T.

The present invention can also be applied to an air-fuel ratio control device that calculates ur (=reference valve opening time TBA s E + below correction value Iou) and opens the electromagnetic on-off valve by the calculated amount valve time TOLIT.

As described above, in the air-fuel ratio control method of the present invention, a correction value representing the error in the reference value is calculated, and a target value corresponding to the target air-fuel ratio to be compared with the output value of the exhaust component concentration sensor is calculated. Since the correction value is changed according to the magnitude of the correction value, the air-fuel ratio can be controlled to the target air-fuel ratio with high accuracy even if the deviation in the base air-fuel ratio of the carburetor becomes large, and the exhaust purification performance can be improved. It can be done.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a device to which the air-fuel ratio 1IJID method of the present invention is applied, Fig. 2 is a block diagram showing the specific configuration of the control circuit in the device of Fig. 1, and Fig. 3 shows the operation of the CPU. The flowchart shown in Fig. 4 is the Do A written in the ROM.
FIG. 5 is a diagram showing the SE data map, FIG. 5 is a diagram showing the Krat data map written in the RAM, and FIG. 6 is a diagram showing the correction value) (rer-target value L ref characteristic. Explanation of the symbols of the 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 sensor 11...Crank angle sensor 12...Cooling water temperature sensor 14... ... Oxygen concentration sensor 15 ... Exhaust manifold 17 ... Throttle valve opening sensor 33 ... Catalytic converter Fig. 1

Claims (1)

[Claims] In an internal combustion engine equipped with an exhaust component concentration sensor in the exhaust system that generates an output according to the concentration of exhaust components in exhaust gas, a reference value for air-fuel ratio control is set according to multiple engine operating parameters related to engine load, and the reference value is set at a predetermined period. The output value of the exhaust component concentration sensor is compared with the target value at each time, and the set reference value is corrected according to the comparison result to determine the output value for the target air-fuel ratio, and the correction represents the error in the reference value. An air-fuel ratio control method for calculating a value, the air-fuel ratio control method comprising: correcting the target value according to the magnitude of the correction value when the correction value is calculated.