JPS61104140A - Control device for air-fuel ratio of engine - Google Patents

Abstract

PURPOSE:To perform stable and high-precise control of an air-fuel ratio, by providing a sampling means which inputs an output from an air-fuel ratio sensor to a comparing means after sampling of the output between ignition signals. CONSTITUTION:A comparing means 16 is provided for comparing an output from an air-fuel ratio sensor 8 with a desired value set by a desired value setting means 15. an air-fuel ratio control means 17 receives an output from the comparing means 16 and controls the air-fuel ratio of air-fuel mixture, fed to an engine, to a desired value. A sampling means 18 is provided for input ting an output from the air-fuel ratio sensor 8 to a coupling means 16 after sampling of the output between ignition signals. This enables stable control of an air-fuel ratio, and permits high-precise and reliable control of the air-fuel ratio through control of the width of an insensitive zone to a low value.

Description

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

(Prior art) Conventionally, I'll kill in engine exhaust gas.
It is widely known that the air-fuel ratio of the engine is detected based on the air-fuel ratio and the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled to a predetermined value.

In this case, the air-fuel ratio sensor that indirectly detects the air-fuel ratio by detecting the oxygen concentration in the exhaust gas has a step-like output (electromotive force) with the oxygen a level corresponding to the stoichiometric air-fuel ratio as the boundary. Changes to There is a so-called λ sensor. This λ
The sensor is suitable for controlling the air-fuel ratio to the stoichiometric air-fuel ratio due to its output characteristics, but it is suitable for controlling the air-fuel ratio to the stoichiometric air-fuel ratio.
When setting the air-fuel ratio to be richer than the stoichiometric air-fuel ratio when high output is required, or when setting the air-fuel ratio to be leaner than the stoichiometric air-fuel ratio to improve fuel efficiency during steady driving at IO speed, As mentioned above, since only the magnitude relative to the stoichiometric air-fuel ratio is determined, it is not possible to accurately detect air-fuel ratios that deviate from the stoichiometric air-fuel ratio to the lean or rich side, and it is difficult to control the air-fuel ratio to an arbitrary value. ] is not suitable for cases where

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, whose output changes linearly according to the oxygen level of 11 degrees in the exhaust gas. The air-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. That is, this wide-range air-fuel ratio sensor has porous 71 electrodes formed on both sides of an oxygen ion conductive solid electrolyte, and PT as the porous electrode on the side that contacts the gas to be measured (exhaust gas).
In addition to using an electrode with semi-catalytic performance mainly composed of A metal oxide such as SnO2, which oxidizes 1-IC to produce co, is present in the vicinity of the three-phase point composed of the 112rff quality and the gas to be measured.

(Problem to be solved by the invention tλ) However, the above-mentioned wide-range air-fuel ratio sensor (as shown in FIG. and ff1W to the electromotive force of this noise
As a result, the output value of the air-fuel ratio sensor changes significantly without corresponding to the air-fuel ratio. (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. ) Therefore, when using the flashing air-fuel ratio sensor to perform feedback control of the engine's air-fuel ratio to a predetermined value, the air-fuel ratio fluctuates greatly due to the noise caused by this ignition signal, and the air-fuel ratio cannot be controlled stably. The problem is that there isn't one.

As a countermeasure, it is possible to create a dead band (hysteresis 1 sis) for the target value of the air-fuel ratio sensor in order to eliminate the influence of noise. However, a problem arises in that the air-fuel ratio control ratio ii'j is reduced by 1J.

The present invention has been made in view of the above, and an object of the present invention is to control the air-fuel ratio based on the output of the air-fuel ratio sensor when no ignition signal is generated when controlling the air-fuel ratio using a wide range air-fuel ratio sensor. By controlling the air-fuel ratio, the air-fuel ratio can be controlled stably without being influenced by noise caused by the ignition signal, and the dead band width can be kept small to accurately control the air-fuel ratio to 1q. It is in.

<Means for Solving the Problems> In order to achieve the above object, the solving means of the present invention is as follows:
As shown in the figure, the air-fuel ratio, which is installed in the engine's exhaust passage and whose output changes depending on the temperature of the exhaust gas, corresponds to the preset air-fuel ratio of the air-fuel mixture. The date (7!) on which the target value of the air-fuel ratio sensor 8 is set (7!) is compared with the target value (lfi) set by the price setting means 15 and the output of the air-fuel ratio sensor 8 and the target value setting means 15. 16, and an air-fuel ratio control means 17 which receives the output of the comparison means 16 and controls the air-fuel ratio of the air-fuel mixture supplied to the engine to the target value. The sampling means 18 for sampling between ignition signals and inputting the sample to the comparison means 16 is configured to be !q.

(Function) With the above configuration, in the present invention, the output changes linearly depending on the oxygen concentration 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, the output of the air-fuel ratio sensor is sampled between the ignition signals, so only the electromotive force that is not superimposed with noise due to the ignition signal is detected by the air-fuel ratio sensor. This will be input to the comparison means as an output value, and the air-fuel ratio will be stably controlled to the target air-fuel ratio without being affected by ignition noise.

Also, since the influence of the large noise caused by the ignition signal 8 is eliminated, the dead band width can be small.
, ``It becomes possible to perform fuel ratio control with high precision and accuracy.

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

FIG. 2 shows an engine air-fuel ratio control 6 according to an embodiment of the present invention.
[1] The schematic configuration of the system is shown in which 1 is an engine, 2 is an intake passage for supplying intake air to the engine 1, and 3 is an exhaust passage for discharging exhaust gas from the engine 1.

The intake passage 2 is provided with throttle valves 1 to 4 that control the amount of intake air supplied to the engine 1, and the intake passage 2 downstream of the throttle valve 4 has a fuel injection valve that injects fuel to the engine 1. A valve 5 is provided.

Further, upstream of the throttle valve 4 in the intake passage 2, an air flow sensor 6 for detecting the amount of intake air and an intake temperature sensor 7 for detecting the temperature of intake air are provided. On the other hand, in the exhaust passage 3, there is an air-fuel ratio sensor 8 that detects the air-fuel ratio based on i carbon f:J degree in the exhaust gas, and an HC sensor 9 that detects hydrocarbon (HC) I[tJ in the exhaust gas. and I
An exhaust temperature sensor υ゛10 is provided to detect the temperature of the air-fuel ratio sensor 8 based on the humidity of the A gas, and the outputs of these sensors 6 to 10 are transmitted to the air-fuel ratio controller 511 that controls the fuel injection valve 5. has been entered. Further, 12 is a spark plug, 13 is an ignition coil, and 14 is an igniter, and the ignition signal 13 from the igniter 14 is inputted to the air-fuel ratio controller 11 as an engine rotational 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 (
A porous electrode such as Pt with semi-catalytic performance is used as the porous electrode on the side that comes into contact with the IJF gas), and a porous electrode near the three-phase point consisting of the electrode, solid electrolyte, and gas to be measured (exhaust gas) is used. , l-I S oxidizes C to produce CO
n○z, In2O3, NiO, Qo a 04, C
It is formed by the presence of metal oxides such as nO, and its electromotive force characteristics are shown in Figure 3.

As shown, the output power changes linearly according to the Rfi J1 degree in the exhaust gas, and the air-fuel ratio can be continuously detected from the rich region to the rich region.
This is a so-called wide-range air-fuel ratio sensor that has the characteristics of the present invention. The electromotive force characteristic of this air-fuel ratio sensor 8 has a temperature α characteristic that changes depending on the temperature (exhaust gas temperature) of the fuel ratio sensor 8, and as the temperature increases, the electromotive force decreases, and the electromotive force increases on the rich side. In addition, the electromotive force characteristic of sensor 8 for the above air-fuel ratio has an HC concentration characteristic that changes depending on the HCC degree in the exhaust gas, and the electromotive force increases as l-lCa1 degree increases on the lean side of the stoichiometric air-fuel ratio. (Note that on the rich side, since the HCiP value is originally high, almost no change in electromotive force occurs).

Next, the operation of the air-fuel ratio controller 11 will be explained with reference to the flowchart shown in FIG.
(l Q 11 on the lean side, 1''' on the rich side) o
''' is a lean side and ridge side delay flag Fit, Fr for distinguishing whether fuel injection is delayed or not.
(“O” when not in delay, ' when in delay)
1'') are both set to ○'', and the feedback coefficient Cfb, which determines the relationship between the engine speed and the injection time, is initially set to P1'', and furthermore, in step S2, the engine speed N is set by the ignition signal from the igniter 14.
In step S3, the intake air flow ff1 is calculated based on the signals from the air 70-sensor 6 and the intake temperature sensor 7.
Calculate ue.

Next, in step S4, the electromotive force Vs as an output signal from the air-fuel ratio sensor 8, the output signal from the I-tC sensor 9, and the exhaust gas temperature signal from the exhaust temperature sensor 10 (air-fuel ratio input the sensor signal).

Furthermore, in step S5, the target air-fuel ratio, HCil
By inputting 1 degree Celsius and exhaust gas temperature 1 degree into a data table as shown in FIG. 5, the slice level median value V as the target tlf+ of the air-fuel ratio sensor 8 corresponding to the target air-fuel ratio
ref is calculated, and the dead band width Vh on the lean side and rich side with respect to the slice level center 1+tlVref as the target value! Find l and Vhr.

In this case, the target air-fuel ratio is set according to the engine operating state using the engine speed and engine load. For example, during high-load operation, the target air-fuel ratio Δ, /F is set to the stoichiometric air-fuel ratio (Δ/F = 14.7). It is set to be richer than the stoichiometric air-fuel ratio, and leaner than the stoichiometric air-fuel ratio during high-speed steady driving. In addition, in the data table shown in FIG. 5 above, slice level medium flame values Vref are written in accordance with exhaust gas mixture and )-ICF:1m for each target air-fuel ratio, and for exhaust gas mixture, From the stoichiometric air-fuel ratio (A/F=14.7>), on the rich side, vref increases with the upper limit of temperature, and on the lean side, Vref decreases with the upper limit of temperature, and the stoichiometric air-fuel ratio increases. Regarding the fuel ratio, VrOf remains almost constant with respect to temperature changes. Also, for HCm*, the stoichiometric air-fuel ratio (A/F=14.
7) On the lean side, as HC Takimaro increases, Vrc
f increases, and at the stoichiometric air-fuel ratio and on the richer side) -1 (VrOf is approximately constant for a 1 m change.Furthermore, the dead band width (that is, hysteresis width) Vh9 with respect to the above-mentioned slice level median value V rcf ．． Vhr is set to eliminate the influence of noise on the output (electromotive force) of the air-fuel ratio sensor 8, and changes by C according to the slice level medium heat 1 + tIVref, that is, the target air-fuel ratio, and is near the stoichiometric air-fuel ratio. is the maximum, and decreases as the air-fuel ratio becomes leaner or richer than the stoichiometric air-fuel ratio.

Thereafter, in the following steps S6'' to S3+, the air-fuel ratio is determined based on the correspondence between the output characteristics of the air-fuel ratio sensor 8 and the average fuel injection amount from the fuel injection valve 5 as shown in FIG. Feedback control is executed to set the target air-fuel ratio by cutting a predetermined dead zone.That is, first, in order to determine the dead zone (hysteresis) of the target electromotive force of the air-fuel ratio sensor 8, the zone flag Fzone is set to It is determined whether the slice level is 0 or 1'', and when Fzone=Q is on the lean side, the slice level center I obtained in step S5 above is determined.
IfJVref, lean side dead band width Vh 9 Step S7 7c S-y Chair L/He/
Let L/median value v'ref be Vr'ef+Vh9, and FZ
For the rich side of One=1, the slice level median value V'ref is set to Vref - Vbr in step S8 using the rich side dead band width Vhr for the slice level median value V ref obtained in step S5, and the process proceeds to step S9. . Then, the electromotive force Vs actually measured from the air-fuel ratio sensor 8 in step S9 and the above-mentioned step S7
Alternatively, it is compared with the slice level median value V' ref determined in S8 to determine whether it is large or small.

When the determination in step S9 is that Vs≧v'ref, the zone flag F zone is determined in step SIG, and when F zone is on the rich side, it is determined that the air-fuel ratio is richer than the target value. Step S
In order to make the air-fuel ratio leaner, that is, reduce the fuel injection amount at
o) (Cr: f5 minute constant), and step S1
2 'Q Warm stone injection time τ is 2K ・(jb-Ve /
There are more oil gaps than Ne. Here, the feedback section i c
The reason why the integral constant Cr of rb is divided by the engine rotational speed NO is because the interval of the culm ignition signal Vi9 at which the engine rotational speed No becomes high is short (so that step S o This is to ensure control stability by reducing the integral constant Or to suppress the increase in time fluctuation of the feedback coefficient Cfb. Wait for the ignition signal vig to rise, and when the ignition signal 19 rises, in the next step S14, the fuel injector current is turned on, and the fuel an is injected from the fuel injector 5.
tJJ, then reset the tζ timer at step S +s, and start the next step S16-(' m
This timer waits for the fuel injection time τ to elapse, and when the fuel injection time τ has elapsed, the fuel injection valve current is turned off in step Sy to end the fuel injection (fuel injection from FJ jt 5. At this time, the ignition , (ffi number vig has completed output. After that, return to step S2, and calculate the electromotive force V from the air-fuel ratio hinge 1-8
Input S signal. That is, during the period from when it is determined in step S13 that the ignition signal vig has risen until it is determined that the ignition signal Vi has risen in step S13, step 84'C: the electromotive force VS signal is When the bow is inserted, the air-fuel ratio sensor 8 is activated during the ignition signal 719 shown in FIG. The power VS is sampled and inputted (marked with a circle in the figure), and the value is held as shown in (C) of the figure.

Thereafter, as the fuel injection amount is decreased in step S12, the air-fuel ratio becomes lean as shown in FIG. make a judgment,
Since it is on the rich side with Fzone = 1, the lean side delay flag F9 is set to "1" in the next step S1!1.

If F9=O is No, it is determined that the process has moved from the rich side to the rich side by one point, and step 320
If the delay flag FQ is set to "1", step 8
Reset the delay timer with 2+ (This delay timer, like the basic timer mentioned above, is a timer that counts up the time from the moment it is reset.) Then, along with the delay time of YES with FQ = 1. In the next step S, the delay timer starts the predetermined delay time j.
It is determined whether dQ has elapsed or not, and if it has not elapsed, the process moves to step S++ and the feedback coefficient Cfb is set as (Jb - (Cr /Nc) to prevent the influence of noise.
), and waits for the rise of the ignition signal ig in step S13 while reducing the fuel injection amount in step S12, and when the signal vi9 rises, the process proceeds to steps SH to SH8.
At step 17, fuel is injected and the process returns to step S2.
4, the electromotive force Vs low signal from the air-fuel ratio sensor 8 is input.

On the other hand, when the delay time tdQ has elapsed, step S2
Step S24 also set the zone flag F zone to ``0'' and the delay flag F9 to ``0'' in step S24.
The feedback coefficient C is set to enrich the air-fuel ratio at
Set rb to Cfb+Cs9 (C52: proportionality constant), step S+2'r increase the fuel injection suspension, and step S1
3, wait for the ignition signal ■ig to rise, and when the signal ■1g rises, fuel is injected in step 5s-8a7, and the process returns to step S1. In step S4, the electromotive force Vs low signal from the air-fuel ratio sensor 8 is detected. input.

Next, since the determination of this fuel injection (step S still occurs even with the increase in J ffi) is VS <■l ref, the zone flag F zone=
It is determined that the lean side is 0, and step S21. To further enrich the air-fuel ratio, set the feedback coefficient Cfb (
:, fb+(C9/Ne) (C9:f?1 minute constant)
(Here, the reason why the branch constant C is divided by the engine rotational speed Ne is the same as in step S12), the fuel injection amount is further increased in step S12, and the ignition signal Vi9 is increased in step SII. Wait for the rise of , and when the (,11?niVi!l!) rises, step S +<~
In step S17, fuel is injected, and the process returns to step S3, where the starting force Vs signal from the air-fuel ratio sensor 8 is input in step S1T.

After that, step S
Although the determination at step S is Vs≧V'raf,
Since the judgment at +o is on the one side of the zone flag l: zone=O, in step S:S it is determined whether the rich side delay flag "r" is "1" or not, and N of Fr = 0 is determined.
When o, it is determined that the change has occurred from the lean side to the rich side, and the delay flag 1"r is set in step S27.
After setting it to 1pa, the delay timer is reset in step 82B. Then, when the Fr-.1 signal is YES during the delay, the delay timer determines whether or not a predetermined delay time tdr has elapsed in the next step 823, and if it has not elapsed, a step is performed to prevent the influence of noise. 825, feedback coefficient CfbJl-cfb
+ (C9/Ne), and while the fuel injection amount is increased in step S12, the ignition is turned on in step S13. g, and when the signal ig rises, fuel is injected in steps 314 to S17, and the process returns to step S2. In step S4, the electromotive force vS signal from the air-fuel ratio sensor 8 is input. On the other hand, as the delay time tdr elapses, the zone flag F zone is set to II and I11 in step Syl, and the delay flag F is set to "O°', and then the air-fuel ratio is not made lean in step S3+. The feedback coefficient Cfb is set as Cfb - Csr (Csr: proportionality constant) to reduce the fuel control IJJ suspension in step S12.
13, when the ignition signal (Via) rises, when the signal v1q rises, steps 314 to 81
In step 7, fuel is injected and the process returns to step S1, followed by step S4.
The electromotive force VS signal from the air-fuel ratio sensor 8 is input. Thereafter, the determination in step SO is VS≧v'ref, the determination in step S+oT'' is F zone-1, and the same operation as above is repeated.

Therefore, the operation flow of the air-fuel ratio controller 11 described in 1.
3, in step $5, the value setting means 1 sets the target value (slice level median value ■ref) of the air-fuel ratio sensor 8 corresponding to the preset air-fuel ratio of the air-fuel mixture.
5. Further, in step S, the output of the air-fuel ratio sensor 8 (electromotive force Vs) and the target value set by the target value setting means 15 (slice level medium heat 1 mV'
ref).

Further, in steps 5111 to S3+, the output of the comparison means 16 is received and the fuel injection amount of the fuel injection valve 5 is controlled.
A constitutes an air-fuel ratio control means 17 that controls the air-fuel ratio of the air-fuel mixture supplied to the engine 1 to the target value. In addition, steps 813 to 817 onibi S2 to S4
This constitutes a sampling means 18 that samples the output of the air-fuel ratio sensor 8 between ignition signals and inputs it to the comparison means 16.

Therefore, in the above embodiment, the air-fuel ratio is detected by the air-fuel ratio sensor 8 whose output (electromotive force) changes in response to the oxygen concentration in the exhaust gas of the engine 1, and the output of the air-fuel ratio sensor 8 and The mixture supplied to the engine 1 is compared with the target 1 shift of the air-fuel ratio sensor 8 corresponding to a preset air-fuel ratio, and the fuel injection amount from the fuel injection valve 5 is controlled according to the deviation. The air-fuel ratio of air is directly feedback-controlled to the target 1 mentioned above.

In this case, the ignition signal V! ! Since the electromotive force VS of the +C air-fuel ratio sensor 8 is sampled,
A stable electromotive force vS on which the noise f: caused by the ignition signal Vig is not superimposed is compared with the slice level median value V'ref as the output value of the air-fuel ratio sensor 8, so that air-fuel ratio control can be performed stably. I can do it. Moreover, since the influence of large noise caused by the ignition (a) is eliminated, the dead band widths VhQ and Vhr can be made small, and the air-fuel ratio can be controlled accurately and accurately.

In the above embodiment, the air-fuel ratio was controlled by controlling the fuel control fJJffl in the fuel injection system, but the air-fuel ratio may be controlled by controlling the air bleed amount in the carburetor system.

(Effects of the Invention) As explained above, according to the present invention, the air-fuel ratio of the engine is adjusted to the set air-fuel ratio using an air-fuel ratio sensor whose output changes depending on the amount of acid N ft in the exhaust gas of the engine. When performing feedback control, sample the output of the air-fuel ratio sensor between ignition signals and control the air-fuel ratio based on the electromotive force that is not distorted by noise caused by the ignition signal! In this way, 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 with good accuracy.
The stability and accuracy of air-fuel ratio control can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention. Figures 2 to 7 illustrate embodiments of the present invention, Figure 2 is a schematic configuration diagram of an engine air-fuel ratio control system, and Figure 3 is a characteristic showing basic characteristics as an electromotive force characteristic of an air-fuel ratio sensor. Figure 4 shows the operation of the air-fuel ratio controller.
- Figure 5 is a diagram showing an example of a data table, Figure 6 is a diagram showing an example of a data table.
The figure is an explanatory diagram showing the correspondence between the output characteristics of the air-fuel ratio sensor and the average fuel injection m, and Fig. 7<a) to (C) show the output of the air-fuel ratio sensor, the ignition signal O, and the output of the V coupling means. This is a full scale drawing. 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, 1 day... Sampling 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. an air-fuel ratio control device for controlling an air-fuel ratio of an engine to the target value, the sampling device sampling the output of the air-fuel ratio sensor between ignition signals and inputting the sample to the comparing means. An air-fuel ratio control device for an engine, characterized in that it is provided with: