JPS6027754A - Air-fuel ratio controlling apparatus for engine - Google Patents

Abstract

PURPOSE:To enable to control the air-fuel ratio exactly, by feedback controlling the air-fuel ratio on the basis of the output value of an oxygen pump type air- fuel ratio sensor constituted by an ion-conductive solid electrolyte. CONSTITUTION:An air-fuel ratio sensor 2 disposed in an exhaust pipe 1 consists of a solid electrolyte oxygen pump 6 consisting of an ion-conductive solid electrolyte (stabilized zirconia) 3 in the form of a plate having a thickness, for instance, of about 0.5mm. and having platinum electrodes 4, 5 attached to both side faces thereof an a solid electrolyte oxygen sensor 10 similarly having platinum electrodes 8, 9 attached to both side faces thereof. These pump 6 and sensor 10 are juxtaposed by a support bed 11, for instance, with a small spacing (d) of about 0.1mm.. The electromotive force (e) kept at a prescribed voltage V1 or V2 by an electronic control unit 12 is changed arbitrarily at predetermined intervals during operation of an engine, and the air-fuel ratio is detected from the output signal corresponding to pump current IP before and after the above changing of the electromotive force (e). Then, the output corresponding to the air-fuel ratio is calculated by judging whether the output of the air-fuel ratio sensor is richer or leaner than the theoretical air-fuel ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for controlling an air-fuel ratio by measuring the oxygen concentration in exhaust gas of an internal combustion engine, etc., and particularly relates to an oxygen pump type device made of an ion-conducting solid electrolyte. This invention relates to an air-fuel ratio control device for an FC engine using an air-fuel ratio sensor.

Conventionally, an oxygen sensor composed of an ion-conducting solid electrolyte (e.g. stabilized zirconia) is used to achieve combustion at the stoichiometric air-fuel ratio by changing the electromotive force caused by the difference between the oxygen partial pressure of the exhaust gas and the oxygen partial pressure of the air. It is well known that, for example, an automobile engine is controlled to operate at a stoichiometric air-fuel ratio by detecting the state.By the way, the above-mentioned oxygen sensor detects the air-fuel ratio (A/ F)
When the stoichiometric air-fuel ratio (A/F) is T = 14.7, a large change in output can be obtained, but in other operating air-fuel ratio ranges, the output changes very little and the stoichiometric air-fuel ratio (v') When the engine is fully operated at an air-fuel ratio other than T, the output of the oxygen sensor cannot be used.

However, an oxygen concentration measuring device using a solid electrolyte element pump as proposed in JP-A-56-130649? An air-fuel ratio sensor was previously invented which can detect an air-fuel ratio (A/F)k other than the stoichiometric air-fuel ratio (A/F)T.

FIG. 1 is a block diagram showing one embodiment of this air-fuel ratio sensor.

In the figure, 1 is an exhaust pipe of the engine, and 2 is an air-fuel ratio sensor disposed within the exhaust pipe 1. The air-fuel ratio sensor 2 has platinum electrodes 4 on both sides of a flat ion-conductive solid electrolyte (stabilized zirconia) 3 with a thickness of about 0.5 van.
. It consists of an upper sensor 10, and a support stand 11 for disposing the oxygen sensor 10' and the oxygen sensor 10'i facing each other with a minute gap d't- of about 0.1 m interposed therebetween. Reference numeral 12 denotes an electronic control unit, which controls the electromotive force ef resistance Rte generated between the electrodes 8 and 9 by the oxygen sensor 10.
The output of the operational amplifier A is proportional to the difference between the electromotive force e and the reference voltage V1 applied to the inverting input terminal (c) of the operational amplifier A through the inverting input terminal (c), while being applied to the non-inverting input terminal (g) of the operational amplifier A. It has a function of driving the transistor TR to control the pump current Ipt flowing through the electrodes 4 and 5 of the oxygen pump.

That is, the electronic control unit 12 is configured such that the pump current Ip' necessary to maintain the electromotive force ef at a predetermined value (1), which is the reference voltage, is supplied from the DC power supply B serving as its supply means; Further, a resistive salt is provided between the output terminals 01.02 to obtain an output signal O8 corresponding to the bond current IP. This resistor corresponds to the DC power source B, and has a desired resistance value selected so that the electric current IP does not flow excessively. C is a capacitor, and S is a switching device for switching the reference voltages vl and v6.

In the above configuration, the oxygen sensor 10 of the air-fuel ratio sensor 2
The electromotive force e generated between the electrodes 8 and 9 is input to the operational amplifier A, whereby an output proportional to the difference between the electromotive force e and the reference voltage vl is applied to the transistor pace.
The pump current IP flowing between the electrodes 4° and 5 of the oxygen bonder 6 is controlled within a predetermined range, and an output signal O8 corresponding to the pump current IP is outputted from the output terminals O1 and 0□, and as described later, one engine It is input to a control means that controls the injectors of the air-fuel ratio and changes the air-fuel ratio.

Figure 3 shows the air-fuel ratio sensor 2't - 20 for domestic passenger cars.
00 cc (D) This is an air-fuel ratio (A/F) and pump current IP characteristic diagram showing the results of a test installed on a gasoline engine.

That is, if an excessive pump current IP flows, the oxygen pump will be destroyed, so the pump current IP may be reduced to 1, for example.
If the DC power supply BK is limited so that the flow does not exceed 00 mA, and the reference voltage Vtk is set to 55 mV, the air-fuel ratio/pump current value characteristic shown in graph a shown in Fig. In this case, the air-fuel ratio/Bonde current characteristics shown in graph b shown in the figure were obtained.

Using the above characteristics, air-fuel ratio (A/F) 'Ft: 1
If an attempt is made to detect in a wide range from 2 to 19, in the characteristic +a) there are two air-fuel ratio points with the same pump current value, so detection cannot be made using only the pump current value.

On the other hand, the characteristic (b) has a drawback in that the Bonde current IP does not change in the range of the stoichiometric air-fuel ratio of 14.7 or less, so the air-fuel ratio cannot be detected in this range.

This invention was made in order to eliminate all the drawbacks of the conventional ones as described above, and the oxygen sensor electromotive force is maintained at a predetermined value Vl or (2) and is switched and changed arbitrarily at a predetermined period during the operation of the entire engine. , by means of detecting the air-fuel ratio based on an output signal corresponding to the Bonde current before and after the switching, the reference voltage V is determined from the difference in the Bonde current at the time of the switching.
Is the air-fuel ratio/current bond characteristic of l on the richer side than the stoichiometric air-fuel ratio?

It is an object of the present invention to provide an air-fuel ratio control device for an engine that can perform footback control to a preset air-fuel ratio depending on the operating state of one engine by determining whether the air-fuel ratio is on the lean side or on the lean side. .

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 is a block diagram showing one embodiment of the present invention. In FIG. 1, 20 is a known four-stroke spark ignition internal combustion engine (hereinafter referred to as engine) mounted on an automobile, and combustion air is supplied to an air cleaner ζ2. Intake pipe 21, throttle valve 23
After inhalation, do it. Further, the fuel is controlled by an injector 24 installed upstream of the throttle valve 23, and the fuel is supplied from the fuel system to the injector 24 (not shown).
Fuel is supplied to. In addition, the throttle valve 23
A pressure sensor 25 is connected to the downstream side of the intake pipe 21 to detect the entire pressure of the intake pipe 21 and convert it into a voltage. The water temperature sensor 26 is made of something like a thermistor whose resistance value changes in accordance with the temperature of the cooling water of the internal combustion engine 1, and the one revolution sensor 27 outputs a full frequency signal corresponding to the number of revolutions of the engine 20. The air-fuel ratio sensor 2 is disposed in the exhaust pipe 1 of the engine 20. The control device 30 includes the pressure sensor 25. Water temperature sensor 262 Rotation sensor 27. By controlling the drive time of the injector 24 based on the output of the air-fuel ratio sensor 2, the air-fuel ratio (A/F) of the engine 20 can be controlled.

As mentioned above, in FIG. 1, the reference voltage k Vs.

When switched to V2 and V2 respectively, the pump current IP of the air-fuel ratio sensor 2 becomes as shown in FIG. It will look like (e) and (d) in Figure 5. In other words, the voltage difference Δ■ across the resistor ito when switching from the reference voltage 't'Vx to V2 is the value △■□ where the air-fuel ratio (4/F) is thinner than the stoichiometric air-fuel ratio (Mk')T. is several times larger than the value ΔV2 on the dark side. Let VS be the voltage across the resistor with respect to the air-fuel ratio (AA') when the reference voltage is Vl, and assume that the voltage VS becomes the value of VCI near the stoichiometric air-fuel ratio (A/F) T, and set the offset voltage' appropriately. i VC2, on the side richer than the stoichiometric air-fuel ratio (84゛) T, the following (1
), and on the thin side, the correction voltage vso of the resistance is expressed in equation (2).
'1 calculation, the value for the air-fuel ratio (A/F) is the 5th
Broken diagram i%13i (4 like el, V'80='
VC2-(Vs-'VC1)...(1).

VSO=VC2+(VS-Vel) (2) Therefore, the correction voltage V81 is calculated by the control device 30 and has a monotonically increasing characteristic with respect to the air-fuel ratio (A/F) detected by the air-fuel ratio sensor 2. There is a one-to-one correspondence with the air-fuel ratio (A/F), and the air-fuel ratio (A/I'') of one engine 20 is controlled as desired.

FIG. 6 is a #g configuration diagram of the control device 30 shown in FIG. 5.
In the figure, the pressure sensor 25 is smoothed by a filter 31, the water temperature sensor 26 is outputted via an interface 32, the output signal 08 shown in FIG. After being input and converted into digital values, these digital data are configured to be input to the microcomputer 38.

The comparator 35 shapes the entire output waveform of the rotation sensor 27.

The counter 36 is configured to measure the entire period from the rise of the output of the comparator 35 to the rise V, and its output is input to the first interrupt terminal ITI of the microcomputer 38. The timer 37 outputs a periodic interrupt signal tone of 5 m5 ec to the second interrupt terminal IT of the microcomputer 38. The microcomputer 38 is a ROM 3 that stores control programs and data.
9 and temporarily store data H, AM 40't-
Built-in.

The timer 41 counts the output pulses of the oscillator 43 according to the trigger signal output from the microcomputer 38 and the set value, and outputs the Norse width corresponding to the set value.
The injector 24 is driven through the dry nozzles 42. h” Rhino F-44 controls the switching device 8 by the output of the microcomputer 38, and sets the reference voltage kVx.
Or switch to N2.

Based on the above configuration 1. A control device 30 according to an embodiment of the invention. In particular, the control operation 2 of the microcomputer 38
This will be explained with reference to the flowchart of the control program shown in FIG. 7 stored in the H,OM 39.

When the power is turned on to the control device 30, the process starts from step 100. At step 100, the output of the microcomputer 38 and the RAM 40'e are initialized.

In step 101, a determination is made every second based on the progress of counting the interrupt signal inputted to the second interrupt terminal IT every S m sec by the second interrupt processing program, and it is determined that one second has elapsed. If so, in step 102 the switching device S
to the opposite side of the current state.

Reference voltage wo ■l to ■2 or ■z to ■! If one second has not elapsed, the process directly advances to step 103.

In step 103, filter 31. Interface 32. The output of the amplifier 33 is sequentially converted into digital values by the AD converter 34 and stored in the RAM 40. Each of these data is expressed as pressure (FB).

Water temperature (WT) and air-fuel ratio data (DSO).

In step 104, the switching device S sets the reference voltage ■! If it is in the direction of the reference voltage V2, proceed to step 105, and if it is in the direction of the reference voltage V2, proceed to step 106.

The process moves to step 107.

In step 105, the air-fuel ratio data (DSO) is stored in data (DSI), and in step 106, the air-fuel ratio data (DSO)! c data (D82) IC storage. Next item.

Stella f107"C above f'-ta (J)82) Kai (D
SI)'(z is subtracted, and if the result is larger than a predetermined value α, it is calculated by the following equation (3) in step 108, and if it is smaller, it is calculated by the equation (4) in step 109, and the process moves to step 110.

(D83) = 02- ((DSI)-C1)...
・(3)(DS3) = C2+ ((DSL) -C
I) ... (4) Here, the data (D83) is a value corresponding to the correction voltage VSO of the above formula (IJ, (21), and the constants CI and C2 are vcl.

This value corresponds to VO2. In other words, equation (3) becomes (1)
The data (DS3) corresponds to the equation (4) and the equation (2) respectively, and the data (DS3) has the same characteristics as (eJ) in FIG. If so, the process moves to step 111, and if it is V'z'R1, the process moves to step 113.In step 111, the engine 20 is calculated from the pressure (FB) and the output cycle of the rotation sensor 27 measured by the counter 36. At the rotation speed (N), data is selected in advance from the target air-fuel ratio table F1 stored in 0M39 and stored in the LAM 40 as target air-fuel ratio data (D84).

In step 112, the air-fuel ratio correction coefficient ゛(I
), data CD83), and (DS4) are used to calculate the following equation (5), and the result is used as a new air-fuel ratio correction coefficient (I).

Therefore, if the switching device S is on the reference voltage Vl side.

Air-fuel ratio correction coefficient C according to data (D83) and (DS4)
I)' is gradually updated, but if it is on the ■2 side, this update is stopped.

In step 113, a drive time table F2 is stored in advance in the ROM 39 with pressure (PB) and rotation speed (N).
All data are selected from , and stored in the RAM 40K as the basic drive time (TO) of the injector 24.

Next, in step ''114, the basic driving time (TO
) is corrected by multiplying it by the air-fuel ratio correction coefficient (I)', and the result is stored in the RAM 40 as the drive time (T1), and step 10
Return to 1. As a result, when an interrupt signal is input to the second interrupt terminal IT2 of the microcomputer 38 in synchronization with the rotation of the engine 20, the drive time (TI)'t timer 41
When the trigger is fully applied, the injector 24 is driven for a time corresponding to this drive time (T1). Therefore, the basic drive time (TO) is adjusted so that the air-fuel ratio (841) detected by the air-fuel ratio sensor 2 matches the target air-fuel ratio (A/F) T data [, the air-fuel ratio correction coefficient CI).
is foot-back controlled and the air-fuel ratio (A/
F ) is controlled to a predetermined value.

As described above, in this embodiment, 1 when the reference voltages 1 and v2 are
Based on the deviation of the output voltage of 40, it was determined whether the air-fuel ratio (A/F) was richer or thinner than the stoichiometric air-fuel ratio (A/F)T. It is okay to make the above judgment.

In addition, the above air-fuel ratio correction coefficient (i)'(il - the above (5
) formula, but the above data (1)83), (1)8
4) Large.

The coefficient (I) may be increased or decreased by a predetermined value, or the driving time (TO) may be corrected in proportion to the deviation of the data (D83) and (D84).

Further, the target air-fuel ratio f-ta (DS4) k the water temperature (W
T) or the acceleration/deceleration state of the engine 2o.

As explained above, according to the present invention, the predetermined value ■! or V
The oxygen sensor electromotive force maintained at By switching the voltage at predetermined time intervals and determining whether the output of the air-fuel ratio sensor is richer or thinner than the stoichiometric air-fuel ratio, it is possible to calculate the output corresponding to the air-fuel ratio, and as a result, it is possible to calculate the output that corresponds to the air-fuel ratio. This provides a great practical effect in that feedback control can be performed to maintain a predetermined air-fuel ratio even in the current state.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an air-fuel ratio sensor used in an embodiment of the present invention, Fig. 2 is a cross-sectional view taken along the line ■-■ in Fig. 1, and Fig. 3 shows the air-fuel ratio sensor shown in Fig. 1. Characteristic diagram showing the test results obtained when installed on a 2000cc gasoline engine, No. 4
FIG. 1 is a diagram showing the entire configuration of an air-fuel ratio control device for an engine according to an embodiment of the present invention. Figure 5 is a characteristic diagram with corrected characteristic sound of Figure 3, Figure 6 is a characteristic diagram of Figure 4.
FIG. 7 is a partially enlarged configuration diagram of the control device shown in the figure, and FIG. 7 is a flowchart of a control program showing the operation of the control device according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Exhaust pipe, 2... Air-fuel ratio sensor, 6... Solid electrolyte oxygen pump, 10... Solid electrolyte oxygen sensor,
12...Electronic control device, 21...Intake pipe, 24...
・Injie II"-, 25...Pressure sensor, 27...
・Rotation sensor. 30...Control device, 31...Filter, 32...
・Interface, 34...AD converter, 3B・
...Microcomputer, 41...Thailand? -, 4
2, 44...driver, 8...-switching device. In addition, in FIG. 1, the same reference numerals indicate the same or equivalent parts. Agent Masuo Oiwa Figure 1 Figure 3 Brass Vacancy (to). Figure 4 Figure 5 Figure 7 Procedural amendment (voluntary) Commissioner of the Japan Patent Office 1, Indication of the case, Japanese Patent Application No. 137115/1982 2, Name of the invention Air-fuel ratio control device for an engine 3, Representative of the person making the amendment Hitoshi Katayama Part 5: Detailed explanation of the invention in the specification subject to amendment. 6. In the detailed description of the amendment, page 8, line 17, "For the darker side, use the following formula (1). The thinner side" should be corrected to "For the thinner side, use the following formula (1) for the foundation side."

Claims (2)

[Claims] (1) A gap part that introduces engine exhaust gas, a solid electrolyte oxygen pump that controls the oxygen partial pressure in this gap, and a solid electrolyte oxygen pump that controls the oxygen partial pressure in the gap and the oxygen partial pressure in the exhaust gas outside the gap. An output signal corresponding to the sonde current of the oxygen pump necessary to maintain the electromotive force generated by the oxygen sensor at a predetermined value is generated depending on the operating state of the engine. In the engine air-fuel ratio control device, the air-fuel ratio of the engine is feedback-controlled so that the air-fuel ratio of the engine is maintained at the predetermined value.
c. means for arbitrarily switching and changing the oxygen sensor electromotive force at predetermined intervals during engine operation, and detecting the air-fuel ratio and correcting the air-fuel ratio of the engine based on the output signals before and after the switching; An air-fuel ratio control device for an engine, characterized by comprising: (2) The means for correcting the air-fuel ratio of the engine shall update all correction coefficients, and the electromotive force of the oxygen sensor maintained at the predetermined value may be changed to two predetermined values, the first voltage and the second voltage. 2. The air-fuel ratio control device for an engine according to claim 1, wherein the air-fuel ratio control device changes the correction coefficient periodically, and completely stops updating the correction coefficient when the voltage is at the second voltage.