JPS61106939A - Air-fuel ratio control device of engine - Google Patents

Abstract

PURPOSE:To improve stability of air-fuel ratio control and accuracy by providing an air-fuel ratio control means controlling the air-fuel ratio of mixture air to an objective value and a control interrupting means interrupting control by the air-fuel ratio control means at a specified time. CONSTITUTION:A comparison means 16 comparing an output of an air-fuel ration sensor 8 with an objective value set by an objective value setting means 15 is provided. An air-fuel ratio control means 17 receives output of the compari son means 16 and controls the air-fuel ratio of the mixture air supplied to an engine to the objective value. When the output cycle from the comparison means 16 is over a predetermined value, a control interrupting means 18 interrupts control by the air-fuel ratio control means 17. Thus, stability of air-fuel ratio control and accuracy can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an air-fuel ratio control means for an engine, and in particular to an air-fuel ratio control means using an air-fuel ratio sensor whose output changes linearly according to the oxygen concentration in the exhaust gas. This invention relates to feedback control of the air-fuel ratio of an engine to a predetermined value.

(Prior Art) Conventionally, it has been widely known to detect the air-fuel ratio of the engine using oxygen IIm in the exhaust gas of the engine and feedback-control the air-fuel ratio of the air-fuel mixture supplied to the engine to a predetermined value.

And in this case, oxygen in the exhaust gas is 1! As an air-fuel ratio sensor that indirectly detects the air-fuel ratio by detecting the air-fuel ratio, the output (electromotive force) changes stepwise with the oxygen concentration corresponding to the stoichiometric air-fuel ratio as the boundary. There is a so-called λ sensor. This λ sensor is suitable for controlling the air-fuel ratio to the stoichiometric air-fuel ratio due to its output characteristics, but when high output is required, such as during acceleration or actual load operation, the air-fuel ratio is lower than the stoichiometric air-fuel ratio. If the air-fuel ratio is set to be richer, or if the air-fuel ratio is set leaner than the stoichiometric air-fuel ratio in order to improve fuel efficiency during steady speed driving, only the magnitude of J' relative to the stoichiometric medium-fuel ratio is determined as described above. Therefore, it is not possible to accurately detect an air-fuel ratio that deviates from the stoichiometric air-fuel ratio to the lean or rich side, and it is not suitable for controlling the air-fuel ratio to an arbitrary value.

Therefore, the present applicant proposed an air-fuel ratio sensor to replace the above-mentioned λ sensor, as shown in Japanese Patent Laid-Open No. 59-100854, in which the output changes linearly according to 1 degree of oxygen Ii in the exhaust gas. The fuel ratio can be detected continuously from the rich region to the lean region.

We have proposed a so-called wide-range air-fuel ratio sensor, which makes it possible to control the air-fuel ratio to an arbitrary value. In other words, this wide-range air-fuel ratio sensor has porous electrodes formed on both sides of an oxygen ion conductive solid electrolyte.
The porous electrode on the side that comes into contact with the constant gas (exhaust gas) is made of Pt or the like and has semi-catalytic performance, and a three-phase electrode consisting of the electrode, a solid electrolyte, and the gas to be measured is used. Near the point, Sn”02 m +7)* m ![11(e
Qh @ # ff 'i! 'u T b 66
(7) T A8° (Problem that 'R Ming attempts to solve) However, as shown in Fig. 3, the wide range air-fuel ratio sensor as described above has a relatively small electromotive force and a large internal impedance, so for example, When a large external noise such as noise generated by an ignition signal is received, the output value of the air-fuel ratio sensor changes greatly without corresponding to the air-fuel ratio due to the Iw of this noise to the electromotive force. (This also applies to the λ sensor mentioned above, but since the λ sensor only determines whether the air-fuel ratio is larger or smaller than the stoichiometric air-fuel ratio, there is no problem even if the output of the sensor changes slightly. ) For this reason,
When the air-fuel ratio of the engine is feedback-controlled to a predetermined value using the wide-range air-fuel ratio sensor, there is a problem that the air-fuel ratio fluctuates greatly due to this external noise, making it difficult to stably control the air-fuel ratio.

As a countermeasure, it is possible to set up a dead band (hysteresis) for the target value of the air-fuel ratio sensor in order to reduce the influence of noise, but as described above: 1. For large noises, set a large dead band width. However, the problem arises that the precision of air-fuel ratio control is reduced.

The present invention has been made in view of the above points, and its purpose is to control the air-fuel ratio based on the output of the air-fuel ratio sensor when external noise is received during air-fuel ratio control using a wide range air-fuel ratio sensor. By not performing fuel ratio control,
The object of the present invention is to stably perform L'U air-fuel ratio control without the influence of external noise, and to suppress the width of the dead zone to a small extent so that the air-fuel ratio control can be performed precisely and precisely.

(Means for solving the problem) In order to achieve the above object, the solving means of the present invention is as follows:
As shown in the figure, an air-fuel ratio sensor 8 is provided in the exhaust passage of the engine, and its output changes depending on the amount of oxygen in the exhaust gas, and the air-fuel ratio sensor 8 corresponds to a preset air-fuel ratio of the air-fuel mixture. Target value setting means 15 for setting the target value of the fuel ratio sensor 8; and comparison means 16 for comparing the output of the air-fuel ratio sensor 8 with the target value set by the target value setting means 15.
and an air-fuel ratio control means 1 which receives the output of the comparison means 16 and controls the air-fuel ratio of the air-fuel mixture to be supplied to the engine to the target value.
The basic configuration includes 7.

Further, a control interrupting means 18 is provided for interrupting the control by the air-fuel ratio controlling means 17 when the output cycle from the comparing means 16 is equal to or greater than a predetermined value.

(Function) With the above configuration, in the present invention, the output changes linearly depending on the degree of oxygen in the exhaust gas.

When feedback controlling the air-fuel ratio to a set value using a so-called wide-range air-fuel ratio sensor, if external noise is superimposed on the electromotive force of the air-fuel ratio sensor and the output of the air-fuel ratio sensor changes significantly, the output of the air-fuel ratio sensor will be affected. When the output cycle of the comparison means increases to a predetermined value or more, and when the output cycle increases, the control by the air-fuel ratio control means is interrupted by the control interrupting means, so that the output cycle is not affected by external noise.
The air-fuel ratio is stably controlled to the target air-fuel ratio.

Furthermore, since the influence of large external noises is eliminated, the width of the dead zone can be small, and it is possible to control the air-fuel ratio with high precision (accurately).

(Example) Hereinafter, an example of the present invention will be described based on the drawings from FIG. 2 onwards.

FIG. 2 shows a schematic configuration of an engine air-fuel ratio control system according to an embodiment of the present invention, in which 1 is an engine, 2 is an intake passage for supplying intake air to the engine 1, and 3 is an engine 1.
This is an exhaust passage for discharging exhaust gas from. - The intake passage 2 is provided with a throttle valve 4 that controls the amount of intake air supplied to the engine 1.
A fuel injection valve 5 for injecting and supplying fuel to the engine 1 is disposed in the downstream intake passage 2 .

Further, upstream of the throttle valve 4 in the intake passage 2, an air sensor 70 for detecting the amount of intake air, a sensor 6, and an intake temperature sensor 7 for detecting lfi It of the intake air are provided. On the other hand, the exhaust passage 3 has oxygen a in the exhaust gas.
an air-fuel ratio sensor IJ8 that detects the air-fuel ratio by m, a 1-IC sensor 9 that detects hydrocarbons (HC) in the exhaust gas, and an exhaust gas sensor that detects the temperature of the air-fuel ratio 8 based on exhaust gas leakage. An air temperature sensor 10 is provided, and the outputs of these sensors 6 to 10 are input to an air-fuel ratio controller 11 that controls the fuel injection valve 5. Also, 12 is a spark plug, 13 is an ignition coil, 1
/1 is an igniter, and an ignition signal from the igniter 14 is inputted to the air-fuel ratio controller 11 as an engine rotation speed signal or the like.

As mentioned above, the air-fuel ratio sensor 8 has porous electrodes formed on both sides of an oxygen ion conductive solid electrolyte, and the gas to be measured (
Use a porous electrode with semi-catalytic performance such as PT as the porous electrode on the side that comes into contact with the gas (111 gas), and use a porous electrode near the three-phase point consisting of the electrode, solid electrolyte, and gas to be measured (exhaust gas). In addition, S which oxidizes 1-IC to produce CO
n O2, r n 203, Ni01C0304, Cn
The electromotive force characteristic is as shown in Figure 3, the output of the electromotive force changes linearly according to the oxygen IIm in the exhaust gas, and the air-fuel ratio changes. This is a so-called wide-range air-fuel ratio sensor that has the basic characteristic of being able to detect continuously from a rich region to a lean region.

The electromotive force characteristic of this air-fuel ratio sensor 8 has a characteristic that changes depending on the exhaust gas intake (exhaust gas mixture) of the air-fuel ratio sensor 8, and as the temperature increases, it becomes leaner than the stoichiometric air-fuel ratio. The electromotive force decreases, and on the rich side, the electromotive force increases. Further, the electromotive force characteristic of the air-fuel ratio sensor 8 changes depending on 1 m of HCII in the exhaust gas.
Has a trend and is leaner than the stoichiometric air-fuel ratio I-I
As the CII value increases, the electromotive force increases (note that on the rich side, there is almost no change in the electromotive force unless the HCI If is originally high).

Next, the operation of the air-fuel ratio controller 11 will be explained with reference to the flowchart shown in FIG. 4. After resetting, in step S+, a zone flag Fzone (on the lean side Pa 0°', rich side "1'°)" to 0°',
Lean side and rich side delay flags r1. for distinguishing whether fuel injection is delayed or not. Fr (“0°’ when not in delay, '1’ during delay)
and the feedback coefficient Cfb, which determines the relationship between the engine speed and the injection side time, are initially set to +11 II, respectively, and in step S2, a basic timer that determines a constant cycle for calculating the engine speed, etc. is reset, and in the next step S3, the basic timer waits for a certain period of time Ti to elapse, and when the certain period of time T1 has elapsed, the basic timer is reset again in step S4. It is a counter that counts up.

Next, in step S5, the engine rotation speed Ne is calculated based on the ignition pulse signal from the igniter 14, and in step S6, the intake air flow rate Ue is calculated based on the signals from the air 70-sensor 6 and the intake temperature sensor 7.

Next, in step S7, the electromotive force Vs multiplied signal as the output signal from the air-fuel ratio sensor 8, the HC concentration signal from the HC sensor 9, and the exhaust gas m* signal from the exhaust temperature sensor 10 (
After inputting the air-fuel ratio sensor Wenlingshin @), step S6
Input the target air-fuel ratio, LI CIIJ degrees and exhaust gas temperature into a data table as shown in Fig. 5.
The slice level median value V ref as a target value of the air-fuel ratio sensor 8 corresponding to the target air-fuel ratio is determined, and the dead band widths Vhl, yhr on the lean side and rich side are calculated with respect to the slice level median value V ref as the target value. seek.

Here, the target air-fuel ratio is set according to the engine operating state according to the engine speed and engine load,
For example, during high-load operation, the target air-fuel ratio A/F is set richer than the stoichiometric air-fuel ratio (Δ/F=14.7), and during high-speed steady running, the target air-fuel ratio A/F is set leaner than the stoichiometric air-fuel ratio. In addition, the data table in Fig. 5 above includes the slice level center @ V ref corresponding to the exhaust gas temperature and 1-I CIII mark for each target air-fuel ratio, and the On the other hand, on the rich R side, with the stoichiometric air-fuel ratio (A/F = 14.7) as the boundary, Vref increases with -1'' on the side, and on the lean side, as the hybrid mixture increases, vrer increases. decreases, and at the stoichiometric air-fuel ratio, Vref remains almost constant for a change of 1. In addition, for 1"Cill Maro, V ref increases with an increase in HCl of 1 degree on the lean side of the stoichiometric air-fuel ratio (A/F = 14.7), and on the stoichiometric air-fuel ratio and richer side than that. V ref remains almost constant for changes in the t-+ ca plane. Furthermore, the dead band width (that is, hysteresis width) VhlVhr with respect to the slice level median value Vref is set to eliminate the influence of noise on the output (electromotive force) of the air-fuel ratio sensor 8. Depending on the air-fuel ratio (9), it is maximum near the stoichiometric air-fuel ratio and decreases as the air-fuel ratio becomes leaner or richer than the stoichiometric air-fuel ratio.

After that, in the following steps 89 to 839, the sixth
The output characteristics of the air-fuel ratio sensor 8 and the fuel injection valve 5 as shown in the figure
Feedback control is executed to bring the air-fuel ratio to the target air-fuel ratio with a predetermined dead zone in correspondence with the average fuel injection amount from . That is, first, the target electromotive force of the air-fuel ratio sensor 8 is not detected.

In order to determine the band (hysteresis), it is determined in step S9 whether the zone flag F zone is "'O" or "1".
"When zone=o is on the lean side" - Step S
Based on the lean side dead zone width Vh intersection with the slice level median value V ref obtained in step 8, the slice level median value V' ref is set to Vref + Vh9 in step 810, and F
On the rich side when ZOne=1, the slice level median value V ref obtained in step S8 is increased by 1.The slice l/bell median value V'ref is set to ■ref-vhr in step S11 using the rich side dead band width Vhr. As,
Proceed to step 812 for each. And step S
In step 12, the actually measured electromotive force VS from the air-fuel ratio sensor 8 is compared with the slice level center 1+IIV'ref determined in step S+o or S++ to determine which one is larger or smaller.

When the determination in step S12 is that Vs≧v'rer, the zone flag F zone is determined in step S13, and when F zone is on the rich side of -1, it is determined that the air-fuel ratio is richer than the target value. Based on this judgment, in step SN, in order to make the air-fuel ratio leaner, that is, to reduce the fuel injection amount, the f-dpock coefficient Cfb is set as Cfb-Cr (Cr:
(integration constant), and in step S
Return to 3.

Thereafter, as the fuel injection tAffi decreases in step S+s, the air-fuel ratio leans toward the lean direction as shown in FIG. After determining the zone, it is the rich side of Fzone=1, so
In the next step S +y, it is determined whether the lean side delay flag F9 is 1'' or not, and when FIll=O is No, it is determined that the change has occurred from the rich side to the lean side, and in the next step S +s, the lean side delay flag F9 is determined to be 1''. Delay flag l”r is “1”
”, and when Fr=O is NO, it is determined that the electromotive force Vs is on the lean side without any abnormality, and the delay flag F9 is set to “1” in step S19.
In step 8n, the delay timer is reset (this delay timer, like the basic timer mentioned above, is a timer that counts up the time from the moment it is reset). In the next step 821, the delay timer determines whether or not a predetermined delay time tdρ has elapsed, and if the delay time has not elapsed, step S14 is performed to prevent the influence of noise.
Then, the feedback coefficient Cfb is maintained at Cfb-Cr, and the process returns to step S3 while reducing the fuel injection amount at step S+s. On the other hand, when the determination in step S+6 is YES (r=1), it means that the reversal from the rich side to the lean side and the reversal from the lean side to the ridge side are rapidly repeated. As shown in Fig. 7, high-frequency external noise is superimposed on the electromotive force of the air-fuel ratio [Nri 8], and it oscillates with an amplitude that exceeds the dead band widths Vh, o, and Vhr, and the above reversal occurs at a period exceeding a predetermined value. Therefore, it is determined that the transition between the rich side and the lean side is repeated, and the delay flag Fr is set to "0"° in step S22.
After closing, the air-fuel ratio control based on the output Vs multiplied signal at that time is interrupted, and the process proceeds to step S14, where the feedback coefficient Cfb is maintained at Cfh-Cr, and the process proceeds to step S+.
At s, the process returns to step S3 with the fuel injection amount reduced.

Then, after the delay times td and Q have elapsed, the zone flag Fzone is set to 'O'km and the caddy delay flag F9 is set to '0' in step 823, and then the process proceeds to step S2.
In order to enrich the air-fuel ratio in 4, the feedback coefficient crb is changed to Cfb+Cs 9 (Cs 9 : proportionality constant)
Then, in step S+s, the fuel injection amount is increased and the process returns to step S3.

Next, even with this increase in fuel injection drowning, the determination in step S12 is still Vs <V' ref, so in step S+s it is determined that the zone flag Fzone=0 is on the lean side, and in step S25 the air-fuel ratio is further adjusted. In order to enrich the feedback coefficient Cfb of
Q ((, Q: integral constant), the fuel injection amount is further increased in step S's, and the process returns to step s3.

Thereafter, due to this increase in fuel injection amount, step S12
The determination in step S becomes Vs≧V' ref.
Since the determination in step 13 is that the zone flag Fzone=O is on the one side, it is determined in step S whether the rich side delay flag Fr is "1" or not, and F r "" N of 0 is determined.
o, it is determined that the transition has occurred from the lean side to the rich side, and in the next step 827, the lean side delay flag r is set.
It is determined whether l is "1°" or not, and when l"e=0 (No), it is determined that the electromotive force Vs is heading toward the rich side without any abnormality, and the delay flag Fr is set to ti 1 in step 828.
After setting to ti, the delay timer is reset in step S. Then, during the delay of YES for Fr-1, the delay timer determines whether or not a predetermined delay time tdr@ has elapsed in the next step S,
If the elapsed time has not elapsed, the process moves to step Sδ to prevent the influence of noise, and the feedback coefficient Cfb is set to Cfb+C.
D, and the process returns to step S3 while increasing the fuel injection time in step S+s. On the other hand, the above step S2
Since the determination in step 7 is YES when FIl = 1, it means that the reversal from the lean side to the rich side and the reversal from the rich side to the lean side are rapidly repeated.
Similar to step S+s above, it is determined that external noise is superimposed on the electromotive force of the air-fuel ratio sensor 8, and step 83
1 and set the delay flag 11 to = 1101″,
The air-fuel ratio control based on the output VS signal at that time is interrupted, the process proceeds to step 825, and -17= feedback coefficient Cfb is maintained at Cfb+CIt, and the process returns to step S3 while increasing the fuel injection amount in step S+s.

Then, when the delay time tar has elapsed, step 83
After setting the zone flag Fzone to °゛1''' and setting the delay flag l''r to 'O'° in step S3.
In Step 3, the feedback coefficient Cfb is set to Cfb - Csr (Csr: proportionality constant) in order to lean the air-fuel ratio, and step S+st' fuel injection 1) II is decreased, and the process returns to C step S3. Thereafter, the determination in step S12 is VS≧V' ref te, and the determination in step S+a is Fz.

ne-1, and the same operation as above is repeated.

Incidentally, the injection timing of the fuel injection valve 5 is determined by the main 70- of the air-fuel ratio controller 11 according to the rise of the ignition pulse from the igniter 14, as shown in FIG.
First, the injection timer was set to the fuel injection time τ. After that, the current to the fuel injector 5 is turned on to start fuel injection.The end of fuel injection is determined by the injection end interleaved signal from the injection timer as shown in FIG. Then, the ink club L is set to J, and the current to the fuel II injection tank 5 is turned off.

Therefore, in the operation flow of the air-fuel ratio controller 11, step S8 sets the target value (slice level median value vrer) of the air-fuel ratio sensor 8 corresponding to the preset air-fuel ratio of the air-fuel mixture. It consists of 15. Further, in step S12, a comparison means 16 is configured to compare the output (electromotive force Vs) of the air-fuel ratio sensor 8 and the target value (slice level median value V' ref ) set by the target value setting means 15. There is. Further, in steps S+3 to S33, the output of the comparison means 16 is received and the fuel injection amount of the fuel injection valve 5 is controlled. 4 j″8″°′J″
i) I:z″″″″″(It I t 61f! 6
fi 17)';! It constitutes an air-fuel ratio control means 17 that controls l It to the above-mentioned target value. Also, step S
I8.822 and S-19=27.831 constitute a control interrupting means 18 which interrupts the control by the air-fuel ratio control means 17 when the output cycle from the comparing means 16 is equal to or greater than a predetermined value.

Therefore, in the above embodiment, the air-fuel ratio is detected by the air-fuel ratio sensor 8 whose output (electromotive force) changes depending on the degree of oxygen in the exhaust gas of the engine 1. The target value of the air-fuel ratio sensor 8 corresponding to the set air-fuel ratio is compared, and the fuel IIj & tolerance amount from the fuel injection valve 5 is controlled according to the deviation, thereby controlling the air-fuel mixture to be supplied to the engine 1. The air-fuel ratio will be feedback-controlled to the target value.

In this case, the slice level median value V'r as the target value
When the output Vs of the air-fuel ratio sensor 8 rapidly repeats reversals between the lean side and the rich side with respect to ef,
It is determined that a large external noise is superimposed on the electromotive force of the air-fuel ratio sensor 8, and the feedback control of the air-fuel ratio at that time is interrupted. The air-fuel ratio is controlled based only on the stable electromotive force VS, and the air-fuel ratio can be controlled stably. Furthermore, the C1 dead band widths VhU and Vhr are small, eliminating the influence of large external noises, and the air-fuel ratio can be controlled very accurately.

21: On the actual flow side, the air-fuel ratio was controlled by controlling the amount of fuel in the fuel injection system.
In the carburetor system, the air-fuel ratio may be controlled by air bleed control.

(Effects of the Invention) As explained above, according to the present invention, the air-fuel ratio of the engine is fed back to the set air-fuel ratio using an air-fuel ratio sensor whose output changes depending on the i1 element concentration in the exhaust gas of the engine. When controlling the air-fuel ratio, the air-fuel ratio control is interrupted when the output fluctuation cycle of the air-fuel ratio sensor exceeds a predetermined value due to external noise, so the air-fuel ratio is controlled only based on the electromotive force that is not superimposed with external noise. In addition, the air-fuel ratio control can be performed stably, the dead band width can be kept small, and the air-fuel ratio control can be performed accurately with good injection, and the stability and accuracy of the air-fuel ratio control can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention. 2 to 9 illustrate embodiments of the present invention, FIG. 2 is a schematic configuration diagram of an engine air-fuel ratio control system, and FIG. 3 is a characteristic showing basic characteristics as an electromotive force characteristic of an air-fuel ratio sensor. Figure 4 is a flowchart showing the operation of the air-fuel ratio controller, Figure 5 is a diagram showing an example of a data table, and Figure 6 is a flow chart showing the operation of the air-fuel ratio controller.
The figure is an explanatory diagram showing the correspondence between the output characteristics of the air-fuel ratio sensor and the average fuel injection amount, Figure 7 is a diagram showing the relationship between the output of the air-fuel ratio sensor and the zone flag state, and Figures 8 and 9 2A and 2B are diagrams illustrating interwoven processing at the start and end of fuel injection, respectively. DESCRIPTION OF SYMBOLS 1... Engine, 3... Exhaust passage, 5... Fuel injection valve, 8... Air-fuel ratio sensor, 11... Air-fuel ratio controller, 15... Target value setting means, 16... Comparison means, 17... Air-fuel ratio control means, 18... Control interrupting means. Figure 7 Figure 5 Figure 6

Claims (1)

[Claims] (1) An air-fuel ratio sensor that is installed in the exhaust passage of the engine and whose output changes linearly according to the oxygen concentration in the exhaust gas, and an air-fuel ratio sensor that corresponds to a preset air-fuel ratio of the air-fuel mixture. target value setting means for setting a target value; comparison means for comparing the output of the air-fuel ratio sensor with the target value set by the target value setting means; and an air-fuel mixture that receives the output of the comparison means and supplies to the engine. air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel ratio to the target value; and control interrupting means for interrupting the control by the air-fuel ratio control means when the output cycle from the comparison means is equal to or greater than a predetermined value. Air-fuel ratio control device for engines.