JPH0315979B2 - - Google Patents

Description

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

Conventionally, an oxygen sensor composed of an ion-conducting solid electrolyte (e.g. stabilized zirconia) has been used to detect a theoretical vacuum due to the change in 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 can be controlled to operate at a stoichiometric air-fuel ratio by detecting a combustion state at a fuel ratio. By the way, the above oxygen sensor measures the air-fuel ratio (A/F), which is the weight ratio of air and fuel.
When the stoichiometric air-fuel ratio (A/F) _T = 14.7, a large change in output is obtained, but there is almost no change in output in other operating air-fuel ratio ranges, and air-fuel ratios other than the stoichiometric air-fuel ratio (A/F) _T When the engine is operated under the conditions of

However, by using a solid electrolyte element pump type oxygen concentration measuring device as proposed in JP-A-56-130649, air-fuel ratios (A/F) other than the stoichiometric air-fuel ratio (A/F) _T can be measured. An air-fuel ratio sensor was invented earlier that could also detect air-fuel ratios.

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

In the figure, 1 is an exhaust pipe of an engine, and 2 is an air-fuel ratio sensor disposed within the exhaust pipe 1. The air-fuel ratio sensor 2 includes a solid electrolyte oxygen pump 6, which is composed of a flat plate-shaped ion-conductive solid electrolyte (stabilized zirconia) 3 with a thickness of approximately 0.5 mm, and platinum electrodes 4 and 5 provided on both sides thereof, respectively. Like the oxygen pump 6, a solid electrolyte oxygen sensor 10 is constructed by providing platinum electrodes 8 and 9 on both sides of a flat ion-conductive solid electrolyte 7. It is composed of support stands 11 that are arranged opposite to each other with a minute gap d of about mm in between. 12 is an electronic control device which applies the electromotive force e generated between the electrodes 8 and 9 by the oxygen sensor 10 to the inverting input terminal (-) of the operational amplifier A via the resistor _R1 ; The output of the operational amplifier A, which is proportional to the difference between the reference voltage V ₁ applied to the input terminal (+) and the electromotive force e, drives the transistor _TR to operate the oxygen pump 6.
It has a function to control the pump current I _P flowing through the electrodes 4 and 5. That is, the electronic control unit 12 is configured such that the pump current I _P necessary to maintain the electromotive force e at a predetermined value _V1 , which is the reference voltage, is supplied from the DC power supply B serving as its supply means. , and the output signal OS corresponding to the pump current I _P
A resistor _R0 is provided between the output terminals _O1 and _O2 . This resistor R ₀ corresponds to the DC power supply B and has a desired resistance value selected so that the pump current I _P does not flow excessively. C is a capacitor,
S is a switching device for switching the reference voltages V ₁ and V ₂ .

In the above configuration, the oxygen sensor 10 of the air-fuel ratio sensor 2 inputs the electromotive force e generated between the electrodes 8 and 9 to the operational amplifier A, and thereby the electromotive force e is proportional to the difference between the electromotive force e and the reference voltage _V1 . The output is applied to the base of the transistor _TR , and the pump current I _P flowing between the electrodes 4 and 5 of the oxygen pump 6 is controlled within a predetermined range, and an output signal corresponding to the pump current I _P is controlled.
The OS is outputted from the output terminals O ₁ and O ₂ and is inputted to a control means that controls the engine injector and changes the air-fuel ratio, as will be described later.

Figure 3 shows the air-fuel ratio sensor 2 installed in a domestic passenger car.
It is an air-fuel ratio (A/F) and pump current I _R characteristic diagram showing the results of a test installed in a 2000 c.c. gasoline engine. In other words, if an excessive pump current I _P flows, the oxygen pump 6 will be destroyed.
I _P is limited by the DC power supply B so that it does not flow more than 100 mA, for example, and when the reference voltage V ₁ is set to 55 mV, the air-fuel ratio/pump current characteristic of graph a shown in FIG. When ₁ was set to 200 mV, the air-fuel ratio/pump current characteristics shown in graph b shown in the figure were obtained.

Using the above characteristics, adjust the air-fuel ratio (A/F) to 12 to 19.
If an attempt is made to detect over a wide range of , in the characteristic (a), there are two air-fuel ratio points with the same pump current value, so detection cannot be performed using only the pump current value. On the other hand, the characteristic (b) had a drawback in that the pump current I _P did not change in the range of the stoichiometric air-fuel ratio of 14.7 or less, so the air-fuel ratio could not be detected in this range.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it is possible to arbitrarily switch and change the oxygen sensor electromotive force, which is maintained at a predetermined value V ₁ or V ₂ , at a predetermined period during engine operation. , the air-fuel ratio/current pump characteristic at the reference voltage V ₁ is determined from the difference in the pump current at the time of the switching to the stoichiometric air-fuel ratio. To provide an air-fuel ratio control device for an engine that can perform feedback control to a preset air-fuel ratio depending on the operating state of the engine by determining whether the air-fuel ratio is on the richer side or the leaner side. The purpose is

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

FIG. 4 is a configuration diagram showing an embodiment of the present invention. In the figure, 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 22, The air is inhaled through the intake pipe 21 and the throttle valve 23. Further, the fuel is controlled by an injector 24 provided upstream of the throttle valve 23,
Fuel is supplied to the injector 24 from a fuel system (not shown). In addition, the above throttle valve 2
A pressure sensor 25 that detects the pressure of the intake pipe 21 and converts it into a voltage is connected to the downstream side of the intake pipe 3. The water temperature sensor 26 is made of something like a thermistor whose resistance value changes depending on the temperature of the cooling water of the internal combustion engine 1.
The rotation sensor 27 outputs a frequency signal according to the rotation speed of the engine 20. The air-fuel ratio sensor 2 is disposed in the exhaust pipe 1 of the engine 20. Control device 30
is configured to be able to control the air-fuel ratio (A/F) of the engine 20 by controlling the drive time of the injector 24 based on the outputs of the pressure sensor 25, water temperature sensor 26, rotation sensor 27, and air-fuel ratio sensor 2. .

As mentioned above, in FIG. 1, the reference voltages are V ₁ ,
When switching to V ₂ and each, air fuel ratio sensor 2
The pump current I _P is as shown in FIG. 3 a and b, and therefore the output OS generated at the output terminals O ₁ and O ₂ at both ends of the resistance value R ₀ is as shown in FIG. 5 c and d. In other words,
The voltage difference ΔV across the resistor R ₀ when the reference voltage is switched from V ₁ to V ₂ is the value ΔV ₁ where the air-fuel ratio (A/F) is thinner than the stoichiometric air-fuel ratio (A/F) _T. It is several times larger than the side value ΔV ₂ . When the reference voltage is V ₁ , the voltage of the resistance R ₀ with respect to the air-fuel ratio (A/F) is VS, and the voltage VS is VC ₁ near the stoichiometric air-fuel ratio (A/F) _T.
Assuming that the offset voltage to be appropriately set is VC ₂ , the value of the resistance R 0 can be calculated using the following equation (1) on the thinner side of the stoichiometric air-fuel ratio (A/F) _T , and using equation (2) below on the richer _side . When the correction voltage VSO is calculated, the value for the air-fuel ratio (A/F) becomes as shown by the broken line e in FIG.

VSO= _VC2- (VS- _VC1 )...(1) VSO= _VC2 +(VS- _VC1 )...(2) Therefore, the correction voltage VSO is calculated by the control device 30 and detected by the air-fuel ratio sensor 2. air-fuel ratio (A/
The air-fuel ratio (A/
There is a one-to-one correspondence with F), and the air-fuel ratio (A/F) of the engine 20 is controlled as desired.

FIG. 6 is a block diagram of the control device 30 shown in FIG. signal
The OS is amplified by an amplifier 33, and each of the above outputs is input to an AD converter 34 and converted into digital values, after which these digital data are input to a microcomputer 38.
The comparator 35 shapes the waveform of the output of the rotation sensor 27, the counter 36 measures the cycle from rise to rise of the output of the comparator 35, and the output is sent to the first interrupt terminal IT ₁ of the microcomputer 38.
configured to input. Timer 37 is
A periodic interrupt signal of 5 msec is output to the second interrupt terminal _IT2 of the microcomputer 38. The microcomputer 38 has a built-in ROM 39 for storing control programs and data, and a RAM 40 for temporarily storing data.

The timer 41 counts the output pulses of the oscillator 43 based on the trigger signal output from the microcomputer 38 and a set value, outputs a pulse width corresponding to the set value, and drives the injector 24 via the driver 42. driver 44
controls the switching device S by the output of the microcomputer 38 to switch the reference voltage to V ₁ or V ₂ .

Based on the above configuration, the control operation of the control device 30, particularly the microcomputer 38, according to an embodiment of the present invention will be explained with reference to the flowchart of the control program stored in the ROM 39 shown in FIG.

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

In step 101, the second interrupt processing program makes a judgment every second based on the progress of counting the interrupt signal inputted to the second interrupt terminal IT ₂ every 5 msec, and determines whether one second has elapsed. If so, step 1
At step 02, the switching device S is controlled to the side opposite to the current state, the reference voltage is switched from V ₁ to V ₂ or from V ₂ to V ₁ , and the process moves to step 103. If 1 second has not elapsed, the process goes directly to step 103. Proceed to.

In step 103, the outputs of the filter 31, interface 32, and amplifier 33 are transferred to the AD converter 3.
4, convert it into digital values sequentially, and store it in RAM4.
Store as 0. Each of these data is converted into pressure (PB), water temperature (WT), and air-fuel ratio data (DS ₀ ).
shall be.

If the switching device S is set to the reference voltage _V1 in step 104, the process advances to step 105, and the reference voltage
If it is in the direction of _V2 , the process of step 106 is performed and the process moves to step 107.

In step 105, the air-fuel ratio data (DS ₀ ) is stored as data (DS ₁ ), and in step 106, the air-fuel ratio data (DS ₀ ) is stored as data (DS ₂ ). Next, in step 107, (DS ₁ ) is subtracted from the data (DS ₂ ), and if the result is greater than a predetermined value α, then in step 108 it is calculated using the following equation (3), and if it is smaller, it is calculated in step 109 as shown in (4). The calculation is performed according to the formula and the process moves to step 110.

(DS ₃ )=C ₂ − ((DS ₁ ) − C ₁ ) …(3) (DS ₃ )=C ₂ + ((DS ₁ )−C ₁ ) …(4) Here, data (DS ₃ ) is the value corresponding to the correction voltage VS ₀ in the above equations (1) and (2), and the constants C ₁ and C ₂ are
This is the value corresponding to VC ₁ and VC ₂ . In other words, equation (3) is
This corresponds to equation (1), and equation (4) corresponds to equation (2), respectively, and the data (DS ₃ ) has the same characteristics as e in FIG. 5.

In step 110, the switching device S switches the reference voltage
If it is the _V1 side, the process moves to step 111, and if it is the _V2 side, the process moves to step 113. Then, in step 111, data is obtained from the target air-fuel ratio table F1 stored in the ROM 39 in advance using the pressure (PB) and the rotation speed (N) of the engine 20 calculated from the output cycle of the rotation sensor 27 measured by the counter ₃₆ . It is selected and stored in the RAM 40 as target air-fuel ratio data (DS ₄ ).

In step 112, the following ((DS)) is calculated using the air-fuel ratio correction coefficient (I) obtained by integrating the deviation between the air-fuel ratio of the engine and the target air-fuel ratio, and the above data (DS ₃ ) and (DS ₄ ). 5) and use the result as the new air-fuel ratio correction coefficient (I).

(I)=(I)-( _DS4 )-( _DS3 )/4...(5) Therefore, if the switching device S is on the reference voltage _V1 side,
The air-fuel ratio correction coefficient (I) is gradually updated using the data (DS ₃ ) and (DS ₄ ), but if it is on the V ₂ side, the pump current output cannot have a characteristic proportional to the air-fuel ratio, so this update is not necessary. Stop.

In step 113, data is selected from the driving time table F ₂ stored in advance in the ROM 39 in terms of pressure (PB) and rotation speed (N), and data is selected from the RAM 40 as the basic driving time (T ₀ ) of the injector 24.
to be memorized. Next, in step 114, the basic drive time (T ₀ ) is corrected by multiplying it by the air-fuel ratio correction coefficient (I), and the drive time (T ₁ ) is set as the RAM 40.
, and return to step 101. As a result, the second interrupt terminal of the microcomputer 38
When an interrupt signal is input to IT ₂ in synchronization with the rotation of the engine 20, the drive time (T ₁ ) is set in the timer 41, and when a trigger is applied, the injector 24 is activated for a time corresponding to this drive time (T ₁ ). is driven.
Therefore, in order to match the air-fuel ratio (A/F) detected by the air-fuel ratio sensor 2 with the target air-fuel ratio (A/F) _T data, the basic driving time ( T ₀ ) is subjected to feedback control, and the air-fuel ratio (A/F) of the engine 20 is controlled to a predetermined value.

As described above, in this embodiment, the air-fuel ratio (A/F) is determined from the deviation of the output voltage of R ₀ when the reference voltages V ₁ and V ₂ are
Although it has been determined whether the air-fuel ratio (A/F) is richer or thinner than the stoichiometric air-fuel ratio (A/F) _T , the above-mentioned determination may be made based on whether it is above or below a predetermined value when the reference voltage is _V2 .

In addition, although the above air-fuel ratio correction coefficient (I) was updated using the above equation (5), the above data (DS ₃ ), (DS ₄ ) were large,
The coefficient (I) may be increased or decreased by a predetermined value, or the driving time (T ₀ ) may be corrected in proportion to the deviation between the data (DS ₃ ) and (DS ₄ ).

Furthermore, the target air-fuel ratio data (DS ₄ ) may be corrected in accordance with the water temperature (WT) and the acceleration/deceleration state of the engine 20.

As explained above, according to the present invention, the predetermined value
Equipped with means for arbitrarily switching and changing the oxygen sensor electromotive force maintained at V ₁ or V ₂ at a predetermined cycle during engine operation, and detecting the air-fuel ratio using an output signal corresponding to the pump current before and after this switching. Depending on the configuration,
By switching the reference 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. This has the great practical effect of being able to perform feedback control to maintain a predetermined air-fuel ratio even during operating conditions.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an air-fuel ratio sensor used in an embodiment of the present invention, and FIG.
Linear cross-sectional view, Figure 3 shows the air-fuel ratio sensor in Figure 1.
FIG. 4 is a characteristic diagram showing the test results obtained when installed on a 2000c.c. gasoline engine. FIG.
6 is a partially enlarged configuration diagram of the control device shown in FIG. 4, and FIG. 7 is a control program showing the operation of the control device according to an embodiment of the present invention. It is a flowchart. 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...Injector, 25...Pressure sensor,
27... Rotation sensor, 30... Control device, 31...
...Filter, 32...Interface, 34...
...AD converter, 38...microcomputer, 41...timer, 42, 44...driver, S...switching device. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1 A gap that introduces engine exhaust gas, a solid electrolyte oxygen pump that controls the oxygen partial pressure in this gap, and a device that corresponds to the oxygen partial pressure in the gap and the oxygen partial pressure in the exhaust gas outside the gap. a solid electrolyte oxygen sensor that generates an electromotive force, and a control means that controls the pump current of the solid electrolyte oxygen pump so as to control the electromotive force to a predetermined voltage, and the first voltage is set so that the characteristic of the pump current with respect to the air-fuel ratio of the engine is reversed near the stoichiometric air-fuel ratio; The characteristics of the engine with respect to the air-fuel ratio are set so that they suddenly change near the stoichiometric air-fuel ratio, and the first and second voltages are arbitrarily switched at a predetermined period to obtain the respective pump currents. An air-fuel ratio control device for an engine, comprising means for correcting the air-fuel ratio of the engine based on a deviation between the air-fuel ratio and a predetermined target air-fuel ratio.