JPH0249658B2 - - 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 in other operating air-fuel ratio ranges there is almost no change in output, and therefore the stoichiometric air-fuel ratio (A/F)
F) When operating the engine at an air-fuel ratio other than _T , the output of the oxygen sensor cannot be used.

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.

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 output terminals O ₁ and O ₂ and 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 above air-fuel ratio sensor 2 for domestic passenger cars.
It is a characteristic diagram showing the relationship between the air-fuel ratio (A/F) and the pump current I _P , showing the results of a test when the pump was installed in a 2000 c.c. gasoline engine. That is, if an excessive pump current I _P flows, the oxygen pump 6 will be destroyed, so the pump current I _P is limited by the DC power supply B so that it does not flow more than 100 mA, and the reference voltage V ₁ is set to 55 mV.
In this case, the air-fuel ratio/pump current characteristic of graph a shown in Fig. 3 also changes to the reference voltage V ₁ .
When the voltage was set to 200 mV, the air-fuel ratio/pump current characteristics shown in graph b shown in the figure were obtained. Note that I ₁ is the control value set for the pump current I _P so that the air-fuel ratio (A/F) of the engine becomes a value close to the stoichiometric air-fuel ratio (A/F) _T.

However, when trying to control the engine to the stoichiometric air-fuel ratio (A/F) _T by using the relational characteristics shown in Figure 3 above, it is possible to determine whether it is rich or lean based on the predetermined pump current I _P. However, since there are two air-fuel ratio (A/F) points for the same value of pump current I _P , it is not possible to use the same control method as when using a normal known oxygen sensor. There were flaws.

The present invention was made in order to eliminate the drawbacks of the conventional devices as described above, and includes an air-fuel ratio sensor having an oxygen pump, a means for driving and controlling the air-fuel ratio sensor, and an air-fuel ratio sensor that operates the air-fuel ratio sensor. An air-fuel ratio control device for an engine capable of controlling the air-fuel ratio to within a predetermined range of the stoichiometric air-fuel ratio, with a configuration including means for feedback-controlling the air-fuel ratio so that the output signal of the control means is equal to or less than a predetermined value. is intended to provide.

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

FIG. 4 is a block 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) installed in an automobile, and combustion air is supplied to an air cleaner 22. , 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. .

FIG. 5 is a block diagram of the control device 30 shown in FIG. 4. In the figure, the pressure sensor 25 is smoothed by a filter 31, the water temperature sensor 26 is outputted via the interface 3, and the output 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 period from rise to rise of the output of the comparator 35 and is configured to input the output to the first interrupt terminal IT ₁ of the microcomputer 38 . Timer 37 is 5msec
A periodic interrupt signal is sent to the microcomputer 38.
It is designed to output to the second interrupt terminal IT ₂ of. 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.

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 output of the microcomputer 38 and the RAM 40 are initialized in step 101 in FIG.

At step 102, the processing from the next step onward is waited until 20 msec has elapsed, and the processing from step 103 onward is performed every 20 msec. This predetermined elapsed time is input to the second interrupt terminal IT ₂ .
It is created by counting signals every 5 msec using the second interrupt processing program.

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 pressure PB,
Water temperature WT and air-fuel ratio data PI.

In step 104, if the air-fuel ratio data PI is larger than a predetermined value α (for example, corresponding to the upper limit control value I ₁ of the pump current of the air-fuel ratio sensor 2 = 10 mA), the process proceeds to step 105; otherwise, the process proceeds to step 1.
11 processing is performed.

In step 105, if the clock CT is zero, a time β (for example, 0.2 seconds) is set in the clock CT in step 106, and the process proceeds to step 107; otherwise, the process of step 113 is performed. The clock CT is executed by the second interrupt processing program mentioned above.
It is counted down every 5 msec until it reaches zero, thereby indicating the elapsed time in which the air-fuel ratio data PI is equal to or greater than the predetermined value α. Further, in step 107, if the mode data M is zero, that is, if the air-fuel ratio data PI up to now is less than the predetermined value α, the process proceeds to step 109; otherwise (M=1), the process proceeds to step 108.

In step 108, the current air-fuel ratio data PI
If the air-fuel ratio data PI1 at time β before is larger than , go to step 109, otherwise go to step 1.
Proceed to step 10. Next, in step 109, the gradient data S is inverted. In other words, if the driving time has been controlled so far in the direction of increasing it, the driving time is controlled in the direction of shortening it, and if not, it is controlled in the direction of increasing it. Also, in step 110, the current air-fuel ratio data is
PI is stored as air-fuel ratio data PI1, and mode data M is set to 1.

On the other hand, if the air-fuel ratio data PI is smaller than the predetermined value α at step 104, the clock CT is set to zero at step 111, and the mode data M is set to zero at step 112, and the process proceeds to step 115.

If the slope data S is zero in step 113, the drive time correction data I is set to a predetermined value in step 114.
C ₁ is increased, and in step 115, the correction data I is set as a constant C ₃ , and if it is smaller, the correction data I is increased by step 12.
Go to 0. On the other hand, in step 113, the gradient data S
If the above correction data I is 1, step 117 is performed.
is decreased by a predetermined value _C2 , and if the correction data I is smaller than the constant _C4 in step 118, the correction data I is set to the constant _C4 in step 119, and if it is larger, the process proceeds to step 120.

In step 120, pressure PB and counter 3
Data is selected from the drive time table F ₁ stored in the ROM 39 in advance using the rotation speed N of the engine 20 calculated from the output cycle of the rotation sensor 27 measured in step 6, and stored in the RAM 40 as the basic drive time T ₀ of the injector 24. do. And step 1
In step 21, the basic drive time T ₀ is multiplied by the drive time correction data I to correct it, and the drive time is set as T ₁ .
The data is stored in the RAM 40 and the process returns to step 102.

Now, when an interrupt signal is input to the first interrupt terminal IT ₁ of the microcomputer 38 in synchronization with the rotation of the engine 20, the drive time T ₁ stored in the RAM 40 is set in the timer 41, and the trigger is activated. Then, the injector 24 is driven for a time corresponding to this drive time T ₁ , and the longer the drive time T ₁ becomes, the more the amount of fuel supplied to the engine 20 increases.

FIG. 7 is a timing chart of the above processing, in which a shows the air-fuel ratio data PI, b shows the driving time correction data I, and c shows the driving time _T1 . In other words, if the air-fuel ratio (A/F) is richer than the stoichiometric air-fuel ratio (A/F) _T at time t ₀ , the control will be on the lean side, so the above correction data I and drive time T ₁ will gradually become shorter. The air fuel ratio (A/F)
approaches the stoichiometric air-fuel ratio (A/F) _T while decreasing.
Next, as can _be seen from the relationship between the air-fuel ratio (A/ _{F) and the pump current I P shown} in _FIG . Therefore, the air-fuel ratio data PI reverses and increases. Next, when the air-fuel ratio data PI exceeds the predetermined value α at time _t2 , the correction data I is inverted,
As a result, the driving time _T1 gradually becomes longer, and the air-fuel ratio (A/F) is controlled to become richer. time
When the air-fuel ratio data PI becomes equal to or greater than the predetermined value α again at _t4 , the correction data I is inverted and the driving time _T1 is gradually shortened. Therefore, the pump current should be adjusted so that the air-fuel ratio data PI is always below the predetermined value α.
Control is performed so that I _P is equal to or less than the upper limit control value I ₁ and the air-fuel ratio (A/F) of the engine 20 is within a predetermined range.
Also, if the air-fuel ratio (A/F) of the engine 20 is richer than the stoichiometric air-fuel ratio (A/F) _T at time t ₅ , but for some reason rich control is performed, then at time t ₆ after β time, The air-fuel ratio (A/F) is automatically switched to the lean side control, and the air-fuel ratio (A/F) is adjusted to the stoichiometric air-fuel ratio (A/F).
F) Controlled so that the value of _T is within a predetermined range.

In addition, in the above embodiment, the control operation for setting the air-fuel ratio (A/F) to a value close to the stoichiometric air-fuel ratio (A/F) _T was explained, but this control operation is also performed in the operating mode (e.g., power enrichment zone, low cooling water temperature). The operation may be stopped depending on the situation (e.g.).

As explained above, according to the present invention, there is provided an air-fuel ratio sensor having an oxygen sensor and an oxygen pump, means for driving and controlling the air-fuel ratio sensor, and an output corresponding to the pump current of the oxygen pump supplied from the control means. The configuration includes means for feedback controlling the air-fuel ratio so that the signal is below a predetermined value, and the pump current flowing through the oxygen pump of the air-fuel ratio sensor is controlled to be below the predetermined value, and the air-fuel ratio is controlled to be equal to or less than the predetermined value. This has the great practical effect of being able to control the fuel ratio within the vicinity of the stoichiometric air-fuel ratio, resulting in excellent engine performance.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an air-fuel ratio sensor used in an embodiment of this 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.
FIG. 4 is a configuration diagram showing an engine air-fuel ratio control device according to an embodiment of the present invention, and FIG. 5 shows the control shown in FIG. 4. FIG. 6 is a partially enlarged configuration diagram of the device, FIG. 6 is a flowchart of a control program showing the operation of the control device according to an embodiment of the present invention, and FIG.
This is a timing chart showing the operation of the main parts of the diagram. 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, 2
4...Injector, 25...Pressure sensor, 2
7... Rotation sensor, 30... Control device, 31...
Filter, 32...Interface, 34...
AD converter, 38...microcomputer, 41...timer, 42...driver. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A gap for introducing engine exhaust gas, a solid electrolyte oxygen pump for controlling oxygen partial pressure in this gap, and oxygen partial pressure in the gap and oxygen in exhaust gas outside the gap. an air-fuel ratio sensor that detects the air-fuel ratio of the engine, the oxygen pump having a solid electrolyte oxygen sensor that generates an electromotive force corresponding to the partial pressure, and an air-fuel ratio sensor that detects the air-fuel ratio of the engine; means for supplying a pump current and driving and controlling the air-fuel ratio sensor by outputting an output signal corresponding to the pump current; and means for feedback-controlling the air-fuel ratio so that the output signal is equal to or less than a predetermined value. An air-fuel ratio control device for an engine, characterized by comprising: 2. The means for feedback controlling the air-fuel ratio is
2. The air-fuel ratio control device for an engine according to claim 1, further comprising a microcomputer having RAM and ROM.