JPH0447784B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an air-fuel ratio sensor, and particularly to an air-fuel ratio sensor suitable for controlling the air-fuel ratio of an automobile engine using an oxygen ion-conducting solid electrolyte.

[Prior art]

An oxygen concentration detector using an oxygen ion conductive solid electrolyte has already been disclosed in SAE paper 810433 and is well known.

However, conventional air-fuel ratio sensors of this type can only measure air-fuel ratios in the lean region and cannot measure air-fuel ratios in the rich region, making them unsatisfactory for use in controlling the air-fuel ratio of automobile engines. . Furthermore, since the reference oxygen concentration is the atmospheric oxygen concentration, there is a drawback that the capacity of the heater for maintaining the solid electrolyte at a high temperature cannot be reduced.

[Purpose of the invention]

The present invention has been made in view of the above, and its purpose is to
An object of the present invention is to provide an air-fuel ratio sensor that can detect an air-fuel ratio even when the air-fuel ratio is <1, and can perform all air-fuel ratio controls.

[Summary of the invention]

The features of the present invention will be described with reference to the reference numerals in FIG. 10, which is an embodiment for convenience of explanation. (a) A solid electrolyte 37 having oxygen ion conductivity is provided with a first and second electrode pair. (b) The first electrode pair 38a, 38b is provided with a diffusion resistor 40 on one electrode side 38b of the first electrode pair 38b that contacts the exhaust gas during exhaust gas, and at least the first electrode pair 38a, 38b , means for reversing the direction of the predetermined current flowing between the two electrodes for detecting a lean region and detecting a rich region of the air-fuel ratio;
When a current is passed through the first electrode pair 38a, 38
(c) On the other hand, the second electrode pair 41a, 41b has one electrode 41a in a reference gas atmosphere (including the atmosphere). ), the other electrode 41b touches the exhaust gas, and at least this second electrode pair 41a, 41b,
A means for outputting the electromotive force E generated between the electrodes constitutes an O ₂ sensor section 59, and (d) In the case of air-fuel ratio detection in a lean region, the outputs V _R and O of the rich/lean detection sensor section 58 are In the case of detecting the air-fuel ratio in the _rich region by the combination with the output O ₂ of the 2 sensor section 59, the air-fuel ratio is determined by the combination of the output V _L of the lean/rich detection sensor section 58 and the inverted output ₂ of the O ₂ sensor section. was set to detect.

Note that the operating principle of the present invention will be explained in detail in the embodiment section based on FIGS. 3 to 7, FIG. 10, and FIGS. 13 to 15, and the explanation here will be omitted.

[Embodiments of the invention]

The present invention will be described below with reference to FIGS. 1, 2, 10 to 1.
Figure 3, Figures 16 to 18, Figure 20, Figure 24
Figures, Figure 27, Figure 29, Figure 33, Figure 36~
The embodiment shown in FIG. 38 and FIGS. 3 to 9,
Figures 14, 15, 19, 21 to 2
This will be explained in detail using FIGS. 3, 25, 26, 28, 30 to 32, 34, and 35.

FIG. 1 is a block diagram showing an embodiment of a control system for an automobile engine equipped with an air-fuel ratio sensor according to the present invention. In FIG. 1, 1 is a throttle chamber, 2 is a hot-wire type intake air amount detector, 3 is an injection valve, 4 is a throttle actuator, 5 is a spark plug, 6 is a water temperature sensor, and 7 is a device according to the present invention. The air-fuel ratio sensor, 8 is a crank angle sensor, 9 is a sensing coil, 10 is a microcomputer, 11 is a control circuit for the air-fuel ratio sensor 7, 12 is a heater control circuit, 1
3 is the combustion chamber, and in this system, the air-fuel ratio is changed from the rich region (λ<1) to the lean region (λ>1).
The air-fuel ratio is detected using an air-fuel ratio sensor 7 capable of detecting the air-fuel ratio over a wide range of air-fuel ratios, and air-fuel ratio control is performed. That is, when the air-fuel ratio to be controlled is determined by the microcomputer 10 based on the rotation speed, load, water temperature, etc., it is output to the injection valve 3 and the slot actuator 4, and the intake air amount is determined by the intake air amount detector 2. is detected and controlled in a closed loop. The air-fuel mixture formed in the throttle chamber 1 enters the combustion chamber 13 and is ignited by the spark plug 5, after which the exhaust gas flows into the exhaust pipe 14. At this time, the actual air-fuel ratio is detected by the air-fuel ratio sensor 7, and the signal is sent to the microcomputer 1.
0 for closed loop control. Note that due to the characteristics of the solid electrolyte used in the air-fuel ratio sensor 7,
Since it is necessary to heat to a high temperature, a heater drive circuit 12 is provided.

FIG. 2 is a detailed configuration diagram of the microcomputer 10 shown in FIG. The analog input signal is the air amount signal from the hot wire intake air amount detector 2.
There are AF, water temperature signal TW from water temperature sensor 6, throttle opening signal θ from throttle actuator 4, etc., and these signals are sent to multiplexer 3.
0, each signal is selected in a time-division manner and sent to the AD converter 31, where it is converted into a digital signal. Information input as an on-off signal includes a signal 11b from the control circuit 11 of the air-fuel ratio sensor 7, which is treated as a 1-bit digital signal. moreover,
Pulse train signal CRP from crank angle sensor 8,
CPP is also entered. 32 is ROM, 33 is CPU
The CPU 33 is a processing central unit that performs digital arithmetic processing, and the ROM 3
2 is a storage element that stores a control program and fixed data. RAM 34 is a readable and writable storage element. I/O circuit 35
sends signals from the AD converter 31 and each sensor to the CPU 33, and sends signals from the CPU 33 to the drive circuit 36 of the injection valve 3, the throttle actuator 4, the ignition coil 9, and the heater drive circuit 12 of the air-fuel ratio sensor 7. It also has the function of sending a control signal 11a to the control circuit 11.

Here, the air-fuel ratio sensor 7 is designed to be able to detect the air-fuel ratio in both the rich and lean regions, and the principle thereof will first be explained. FIG. 3 is an explanatory diagram of the principle of the air-fuel ratio sensor 7. FIG. 3a shows the detection principle in a lean region, and FIG. 3b shows the detection principle in a rich region. As shown in FIG. 3, positive and negative electrodes 3 are placed on both sides of the solid electrolyte 37.
8a, 38b (equivalent to the first electrode pair of the present invention, and a diffusion chamber 40 is provided via an orifice 39 that serves as a gas diffusion resistance. When detecting the air-fuel ratio in a lean region, , as shown in FIG. 3a, the electrode 38a is an anode, the electrode 38b
is used as a cathode, and a voltage is applied so that a current flows in the direction shown. At this time, oxygen proportional to the current passes through the solid electrolyte 37 and is pumped out from the diffusion chamber 40. Further, when detecting the air-fuel ratio in the rich region, as shown in FIG. 3b, a voltage is applied so that the current flows in the opposite direction to the above, using the electrode 38a as the cathode and the electrode 38b as the anode. At this time, oxygen flows into the diffusion chamber 40 from the exhaust side.
Thereafter, carbon monoxide (CO) flowing in through the orifice 39 reacts with the carbon dioxide (CO) in the diffusion chamber 40 as shown in the following equation.

CO+1/2O ₂ →CO ₂ ...(1) In this way, both the diffusion chamber 4 in Figure 3 a and b
Condition in which the partial pressure of oxygen within 0 is extremely low (10 ^-12 atm)
, and the inside of the diffusion chamber 40 is always kept at a stoichiometry (λ
= 1.0 exhaust condition), a change in electromotive force occurs.

The principle will be explained in more detail below using FIGS. 4 and 5. FIG. 4 is a diagram illustrating the principle of detection in a lean region. Orifice 39 due to gas diffusion
The amount of oxygen that enters the diffusion chamber 40 via G _fK is proportional to the concentration of oxygen in the exhaust gas N _fe . That is, G _fK = K・N _fe ...(2) where, K: constant Therefore, as shown in FIG. 4a, the diffusion chamber 40
The amount of oxygen that enters the interior by diffusion increases as the excess air ratio λ increases. Also, when a current is applied as shown in Figure 3a, the current [Figure 4a
₁ , ₂ ] is pumped out from the diffusion chamber 40. In other words, when a current of ₁ is applied, the amount of oxygen pumped out becomes larger when λ<λ ₁ , and as shown in FIG. ^-12 atm), and as in a normal oxygen sensor, the electromotive force is as shown in Figure 4b.
Approximately 1V is output. Also, in the region of λ>λ ₁ ,
Since the amount of oxygen that enters the diffusion chamber 40 by diffusion is greater than the amount of oxygen pumped out, the oxygen partial pressure within the diffusion chamber 40 increases, and the solid electrolyte 37
There is no difference between the oxygen partial pressures on both sides, and no electromotive force is generated. In other words, a current _{of 1} causes a change in electromotive force when λ=λ ₁ . Also, at current ₂ ,
A change in electromotive force occurs when λ = λ ₂ . This electromotive force change point (for example, λ ₁ , λ ₂ ) becomes the control point when performing air-fuel ratio control in the lean region, and the current (for example,
₁ , ₂ ) can be set arbitrarily.

FIG. 5 is an explanatory diagram of the detection principle in the rich region. In the rich region, λ is detected based on the amount of carbon monoxide that diffuses into the diffusion chamber 40. At this time, as shown in FIG. 3b, the diffusion chamber 40
Oxygen is sent into the interior via a solid electrolyte 37.
₁ , when λ>λ ₁ , the amount of carbon monoxide entering the diffusion chamber 40 is smaller than the amount of oxygen consumed by the reaction shown in equation (1) As shown in FIG. 5d, a large amount of oxygen is retained in the diffusion chamber 40,
The oxygen partial pressure in the diffusion chamber 40 becomes higher than the oxygen partial pressure in the exhaust gas in the rich region, and a difference in oxygen partial pressure occurs on both sides of the solid electrolyte 37, generating an electromotive force as shown in FIG. 5b. Furthermore, when λ<λ ₁ , the amount of carbon monoxide entering the diffusion chamber 40 increases, and most of the oxygen sent into the diffusion chamber 40 is consumed by the reaction of equation (1), as shown in FIG. 5c. Then, the oxygen partial pressure in the diffusion chamber 40 becomes smaller and becomes equal to the oxygen partial pressure in the exhaust gas, so that no electromotive force is generated, as shown in FIG. 5b. Furthermore, if the current value is changed to ₂ , λ ₂ will be detected. These λ ₁ and λ ₂ are the air-fuel ratio control points in the rich region, and can be arbitrarily set by the values of currents ₁ , ₂ , etc.

As described above, by changing the direction of the current flowing through the solid electrolyte 37 and variably setting the level of the predetermined current value, it is possible to set the air-fuel ratio control point in a wide range from the lean region to the rich region. can be detected.

The results measured as above are shown in Figures 6 and 7.
As shown in the figure. Figure 6 shows the case in the lean region.
= 2mA, as in curve a, A/F = 15
The electromotive force changes with (A: air amount, F: fuel amount),
= 4mA, as shown in curve b, A/F = 16
The electromotive force changes. In addition, due to the oxygen partial pressure difference,
Even at λ=1.0, the electromotive force changes, resulting in a two-position change. Since a two-position change results in two air-fuel ratio control points, it is necessary to avoid this. Countermeasures against this will be described later.

Figure 7 shows the case in the rich region, as shown in curves c and d, when = 2mA, A/F = 14.3,
= 4mA, the electromotive force changes at A/F = 13.6. Also, at this time, the electromotive force changes even around λ=1.0, and countermeasures for this will be described later.

The above method is a method of keeping the current constant and observing changes in electromotive force, but it is also possible to keep the applied voltage constant and detect A/F from changes in current. 8th
9 are diagrams showing measurement examples in that case. FIG. 8 shows the case in the lean region, and when the voltage is changed, a limiting current ₀₂ proportional to the oxygen concentration (%) is obtained. Figure 8a shows the relationship between voltage and limiting current using oxygen concentration as a parameter, and curves e to g show oxygen concentrations of 2, 4, and 6%, respectively.
The case is shown below. FIG. 8b shows the oxygen concentration and limit current when V=0.5V is kept constant, and it can be seen that a current ₀₂ proportional to the oxygen concentration is output. Here, the voltage applied to the solid electrolyte 37 is
Maintaining the pressure at 0.5 means controlling the oxygen partial pressure in the diffusion chamber 40 to always maintain it at 10 ^-12 atmospheres (stoichiometry, exhaust state with λ=1.0). That is, when the oxygen concentration increases and the amount of oxygen entering the diffusion chamber 40 increases, the current is increased to pump out the increased amount of oxygen and maintain the oxygen partial pressure at 10 ^-12 atmospheres. That is, when the oxygen concentration in the exhaust gas increases, the current ₀₂ increases.

FIG. 9 shows the measurement results in the rich region. Figure 9a shows the relationship between voltage and limiting current using carbon monoxide concentration (%) as a parameter, and curves h to j are carbon monoxide concentrations of 2 and 2, respectively.
Figure 9b shows the relationship between carbon monoxide concentration and limiting current when V=0.5V is constant. Here, since the oxygen concentration in the exhaust gas is in a stoichiometric state, more oxygen than is consumed in equation (1) is sent into the diffusion chamber 40 to increase the oxygen partial pressure, and V = 0.5V. It always tries to maintain the partial pressure difference. Therefore, as shown in FIG. 9b, as the carbon monoxide concentration increases, the limiting current _cp also increases.

FIG. 10 is a basic conceptual diagram of the configuration of an air-fuel ratio sensor for putting into practical use the principle explained above. Platinum electrodes 38a and 38b are provided on both sides of the solid electrolyte 37, and a diffusion chamber 40 having an orifice 39 is provided on the electrode 38b side. The current flowing between the electrodes 38a and 38b is switched between forward and reverse directions. Moreover, as shown in FIGS. 6 and 7, λ=
In order to avoid a change in electromotive force when λ = 1.0, an electrode 41a on the atmosphere side and an electrode 41b on the exhaust side are further provided as shown in the figure in a normal oxygen sensor whose electromotive force changes when λ = 1.0 (avoidance). The law will be discussed later). The electrodes 41a and 41b are the second electrodes of the present invention.
corresponds to an electrode pair of In addition, a heater 42 for heating the solid electrolyte 37 to a high temperature is connected to the solid electrolyte 37.
print on top. 58 and 59 are electrodes 38, respectively.
A rich lean detection sensor consisting of portions a and 38b and an O ₂ sensor consisting of electrodes 41a and 41b are shown.

FIG. 11 is a longitudinal sectional view showing an embodiment of the air-fuel ratio sensor of the present invention. In FIG. 11, 37 is a solid electrolyte, and the solid electrolyte 37 includes electrodes 38a, 38b, 41a, 41 as shown in FIG.
b and a heater 42 are added, and the sensor part 4
3 is formed. The sensor section 43 is inserted into the center of a holder 44 made of ceramic. Reference numeral 45 denotes a cap, and the cap 45 is provided with a vent hole 45a for guiding the atmosphere to an atmospheric chamber 46 at the center of the holder 44. A stopper 47 is inserted into a hole 53 (see FIG. 12) provided in the sensor section 43, and is used to fix the sensor section 43. The stopper 47 is made of ceramic and is incorporated into a holder 48 made of ceramic. The tip of the sensor section 43 (the side on which the diffusion chamber 40 is provided) is protected by a cover 49, and the cover 49 is provided with a ventilation hole 50 through which exhaust gas is introduced into the exhaust chamber 51. It is set as. Note that the cover 49 is
It is made of ceramic to prevent heat dissipation due to radiation from the heater 42 (see FIG. 12). And the whole is an external cover 52 for attaching to the exhaust pipe.
The cover 52 is fixed to the holder 44 with a caulking portion 53.

FIG. 12 is a detailed structural explanatory diagram showing one embodiment of the sensor section 43 in FIG. 11, in which a is a sectional view, b is a left side view of a, c is a right side view of a, and d is an A- It is an A-line sectional view. The sensor section 43 is mainly composed of a rectangular solid electrolyte 37, and on one side, as shown in FIG. As shown in c, the other side is printed with an electrode 38b for detecting the air-fuel ratio in the rich/lean region, an electrode 41a on the atmosphere side for detecting the electromotive force at λ=1.0, and an electrode on the exhaust side. Electrode 41
b is printed on it. Furthermore, a hole 53 into which a stopper 47 shown in FIG. 11 for fixing the sensor section 43 is inserted is provided. The portion where the heater 42 is printed is coated with a ceramic coating 54 to prevent the heater 42 from peeling off, as shown in FIG. 12d.

FIG. 13 is a configuration diagram showing an embodiment of the overall configuration of the air-fuel ratio sensor of the present invention including a control circuit and a signal processing circuit. 14 is an exhaust pipe, and an air-fuel ratio sensor 7 is attached to the exhaust pipe 14. 12 is heater 4
2, a control circuit 55 reverses the direction of the current flowing between the electrodes 38a and 38b, and 11 a relay circuit that makes the current flowing between the electrodes 38a and 38b a constant current, and processes the output signal so that the current flows in the rich region. A control circuit 56 outputs V _R and V _L in the lean region, and 56 is the electrode 41a and 4 when λ=1.0.
An inversion circuit 57 outputs an electromotive force signal 56a (O ₂ ) generated between 1b and a signal 56b ( ₂ ) obtained by inverting it, and 57 calculates (V _L +O ₂ ) and (V _R + ₂ ). These are adder circuits that output signals 57a and 57b corresponding thereto. As a result, Figure 6,
The two-position problem explained in FIG. 7 can be avoided.

Here, the concept of signal processing of this embodiment including avoidance of the two-position problem will be explained. FIG. 14 is a diagram illustrating signal processing in a lean region. a is the output signal V _L 1 from the rich/lean detection sensor 58 when a certain value of the set current 11a is input to the control circuit 11
This is the waveform of 1b. As described above, this signal V _L changes in magnitude at a certain air-fuel ratio in the lean region, but it also changes at λ=1.0.
b is the waveform of the signal 56a outputted from the inverting circuit 56 and changing at λ=1.0. c is the signal of a
This is the waveform of a signal 57a (V _L +O ₂ ) obtained by adding V _L and signal 56a (O ₂ ) of b in an adder circuit 57. The signal 57a obtained in this way does not change except for the air-fuel ratio in the lean region,
This makes it possible to solve the two-position problem described above. Note that the signal V _L is outputted from the rich/lean detection sensor 58 made up of the electrodes 38a and 38b, and the signal 56a is outputted from the O ₂ sensor 59 made up of the electrodes 41a and 41b.

FIG. 15 is a diagram illustrating signal processing in a rich region. a is the waveform of the signal V _R , and in this case, the relay circuit 55 reverses the direction of current flow to obtain the signal V _R. b is the waveform of a signal 56b obtained by inverting the signal 56a from the O ₂ sensor 59 at the slice level by the inverting circuit 56. A signal 57 obtained by adding these two signals in an adder circuit 57
The waveform of b is shown in c. In this case as well, the two-position problem is solved as above.

That is, in the case of air-fuel ratio detection in the lean region, the adder circuit 57 uses the output V _L of the rich/lean detection sensor section 58 and the output O ₂ of the O ₂ sensor section 59.
For air-fuel ratio detection in the rich region, in combination with
Output V _R and O ₂ of rich/lean detection sensor section 58
By combining with the inverted output ₂ of the sensor section 59,
This enables air-fuel ratio detection.

FIG. 16 is a specific circuit diagram of the relay circuit 55 and control circuit 11 shown in FIG. 13. Control circuit 1
1 is a circuit 11A that supplies a constant set current o to the rich/lean detection sensor 58, and processes the signal (electromotive force) from the sensor 58 into on/off signals that change at the slice level to generate signals V _L and V _R It consists of a circuit 11B that outputs. Circuit 11A
inputs the analog value 11a of the current setting signal from the computer 10 (see Figure 1) output from the DA converter, and inputs this and the voltage proportional to the current o generated by the resistor 60 to the comparator 61. The transistor 62 is operated by the output of the comparator 61, and the current is controlled by the transistor 63. The circuit 11B converts the electromotive force, which is the output signal from the rich/lean detection sensor 58, into a signal 11b of 0 and 1 using a comparator 64.
(V _L , V _R ). The relay circuit 55 switches the direction of the current flowing through the sensor 58 between positive and negative directions according to rich control and lean control using a control signal 55a from the computer 10.

FIG. 17 is a circuit diagram showing an embodiment of the inversion circuit 56 of FIG. 13. The signal from the O ₂ sensor 59 that detects the electromotive force at λ=1.0 is input to the comparator 65 and compared with the slice level V _s ,
Outputs an _O2 signal 56a which is an on/off signal,
Further, this signal is inverted by the transistor 66, and the transistor 66 also outputs the ₂ signal 56b.

FIG. 18 is a circuit diagram showing an embodiment of the adder circuit 57 in FIG. 1. This circuit adds the signal V _R and the signal 56b to produce the signal 57b.
It adds V _L and O ₂ signal 56a and outputs signal 57b, and is composed of two sets of circuits shown in FIG. 18.

By the way, in an automobile engine, λ is controlled as shown in FIG. 19 according to the rotational speed and load. The map shown in FIG. 19 is stored in the computer 10, and the set current signal 1 is set based on this map.
1a is output to circuit 11A.

FIG. 20 is a flowchart of the λ control process. First, operating parameters such as rotation speed and load signal are read, and λ is determined from the map shown in FIG. Next, calculate the fuel amount G ₁ and injector 3
Calculate the valve opening time u (see Figure 1). next,
Find the set current. λ to be controlled is λ＞
1, the (V _L +O ₂ ) signal 57a
Check whether is on or off, and if it is on, reduce the correction amount w and add (w - Δw) to u. If it is off, w is increased and (w+Δw) is added to u. On the other hand, if it is a rich region with λ<1, the opposite is true: it is checked whether the (V _R + ₂ ) signal 57b is on or off, and if it is on, w is increased, and if it is off, w is decreased and added to u. .

Next, a method for correcting dead time due to exhaust delay will be explained using FIGS. 21 and 22.
The dead time referred to here is the time _t1 shown in FIG. 21 from when the injection valve 3 operates until the rich lean detection sensor 58 responds. This means the time it takes for the air-fuel mixture to enter the combustion chamber 13 and for the combusted exhaust gas to pass through the exhaust pipe 14 and reach the air-fuel ratio sensor 7. FIG. 21a is a diagram showing the relationship between the rotational speed and the dead time t ₁ , and as the rotational speed increases, the dead time t ₁ decreases. FIG. 12b is a diagram showing the relationship between load and t ₁ , in which t ₁ decreases as the load increases. In other words, t ₁ changes two-dimensionally depending on the rotation speed and load.

Next, with reference to FIG. 22, the influence of dead time _t1 on control and the correction method will be explained. If you try to change λ according to the instructions from the computer 10, what happens if the amount of fuel decreases due to the operation of the injection valve 3 as shown in Figure 22a, and the set current (1) ₁ as shown in Figure 22b. Assuming that the changes are made simultaneously, in the lean region, the ability to pump oxygen from the diffusion chamber 40 increases due to the increase in current,
The oxygen partial pressure in the diffusion chamber 40 decreases even though there is no change in the oxygen concentration in the exhaust gas, the interior of the diffusion chamber 40 becomes more oxygen diluted than the stoichiometric state, and the time t a until the exhaust gas reaches the sensor 7 _is During this period, as shown in FIG. 22c, a high electromotive force is generated from the sensor 7, resulting in an uncontrollable time period. However, if you change the temperature after the exhaust gas reaches sensor 7,
This will not happen. As shown in Figure d, the above problem can be solved by changing the set current (2) ₂ with _a delay of the dead time ta due to the exhaust delay, such as ₂ . The same is true when increasing the amount of fuel; change ₂ with a delay of the dead time t _b to avoid problems. Note that this dead time varies depending on the rotation speed and load as shown in FIG. 21, so correction is made according to FIG. 21. Furthermore, it goes without saying that the dead time _t1 may be measured and corrected using the sensor output and the clock counter. With the above, it is possible to solve the problem of uncontrollable time due to changes in the set air-fuel ratio.

Additionally, when the sensor temperature changes, the output changes. Next, a method for controlling the sensor temperature will be explained. FIG. 23a is a diagram showing the relationship between voltage and current of the rich/lean detection sensor 58 using temperature as a parameter. Curves k to m are sensor temperatures T ₁ , T ₂ , T ₃ (however, T ₁ > T ₂ > T ₃ ). When the sensor temperature changes, the specific resistance of the solid electrolyte 37 decreases, making it easier for oxygen to flow. Therefore, as shown in Figure 23a, the higher the sensor temperature, the lower the voltage and the lower the limit current.
₁ will start flowing. In the case of temperature T ₃ , the control signal changes between ΔV _T3 with a peak value of V _{P (T3)} . This situation is shown in FIG. 23b. Second
As can be seen from Figure 3b, the sensor temperatures T ₁ , T ₂ ,
Due to T ₃ , the peak value of the control signal V _P(T1) , V _P(T2) ,
V _P(T3) changes. In other words, by reading this V _P , you can tell whether the temperature is appropriate. For example, if T ₂ is the optimal temperature, T ₁ is too high and V _P decreases,
T ₃ is too low and V _P will rise. Since this V _P changes depending on the current, V _P must be mapped according to the set current.
Note that the slice level at this time is (V _P +
V _B )/2 (V _B is shown in FIG. 23b), it is possible to cope with changes in V _P.

FIG. 24 is a circuit diagram showing an embodiment of the heater control circuit 12 of FIG. 13. The above-mentioned measurement
The comparator 67 compares V _P and the optimum V _P and supplies an on-off duty signal according to the amount of deviation to the transistor 68.
₈ controls a relay switch 69 that turns on and off the heater power supply circuit.

Next, the advantages of using the above-described air-fuel ratio sensor according to the present invention during startup and warm-up will be explained.
Figure 25a is a diagram showing the relationship between time immediately after startup and mixture concentration using water temperature as a parameter; n,
The o curves show the relationships when the water temperatures are T ₁ and T ₂ , respectively. Immediately after starting, the mixture concentration is increased, and becomes thinner as time passes, that is, as the water temperature increases. In other words, during warm-up operation, if an appropriate A/F is applied depending on the cooling water temperature, the engine can be operated without waste. By the way, since the air-fuel ratio sensor 7 according to the present invention can operate even in a rich region, it enables rich mixture control immediately after starting. Second
If the relationship between water temperature and A/F shown in FIG. 5b is recorded in the computer 10, the system can be operated according to this function during warm-up. FIG. 25c is a control block diagram at this time. The signal of the water temperature sensor 6 is inputted to the computer 10, and FIG.
The A/F is determined from a function showing the relationship between the two, and is output to the engine system 70. The air-fuel ratio sensor 7 detects the actual air-fuel ratio, compares this output with the output indicating the A/F from the computer 10, and performs closed-loop control to optimally control the A/F during warm-up. Can be done.

It is also necessary to control the ignition timing due to changes in the air-fuel ratio, and this can also be useful. FIG. 26 is a diagram showing the relationship between A/F and ignition timing using rotation speed as a parameter.
If the A/F is large, the flame propagation delay is large, so the ignition timing must be advanced. In addition, the load is also a parameter for ignition timing, so
Ignition timing must be controlled using a three-dimensional map of A/F, rotation speed, and load, but control using A/F can be easily realized.

FIG. 27 is a sectional view showing another embodiment of the present invention, and the same parts as in FIG. 10 are designated by the same reference numerals, and their explanation will be omitted. In FIG. 27, in addition to a diffusion chamber B corresponding to the diffusion chamber 40 in FIG.
A diffusion chamber A is provided which also includes 1b. The oxygen partial pressures P _A and P _B in the diffusion chambers A and B are: P _A = P _M + β _A − β _B … (3) P _B = P _A − β _B … (4) Where, β ; constant _A ; Current _B flowing between electrodes 41a and 41b; Current P _M flowing between electrodes 38a and 38b; Oxygen partial pressure in exhaust gas. From equations (3) and (4), P _B = P _M + β _A −2β _B …(5) holds true. Therefore, _B for which P _B =0 is _B = P _M +β _A /2β …(6), and P _M =0, that is, excess air ratio λ = 1
However, if _A > 0, as shown in Figure 28,
_B does not become 0. In the rich region where λ<1, the reaction CO ₂ CO + 1/2O ₂ ...(7) progresses, and if this reaction is balanced in the diffusion chamber A, the oxygen in the diffusion chamber A will be consumed by the oxidation of carbon monoxide. Ru. As the amount of carbon monoxide in the exhaust gas increases, the amount of carbon monoxide that enters the diffusion chamber A through diffusion increases, so the amount of oxygen in the diffusion chamber A decreases. That is, oxygen becomes zero at point c in FIG. 28, and a signal corresponding to λ can be obtained.

Furthermore, in the configuration shown in FIG. 27, _A may be controlled so that _B is constant and P _B becomes zero. In this case, _A = 2β _B − P _M /β (8) is obtained from equation (5), and as P _M increases, _A decreases.

FIG. 29 is a basic configuration diagram corresponding to FIG. 10 showing still another embodiment of the present invention, and the same operating parts are indicated by the same reference numerals. In FIG. 29, the diffusion chamber 40 of FIG. 10 is replaced with electrodes 38a and 41a.
The oxygen partial pressure within the diffusion chamber 40a is accurately controlled to obtain an output proportional to the A/F. 80 indicates a first sensor, and 81 indicates a second sensor. FIG. 30 is an output characteristic diagram of the second sensor 81. Oxygen in the diffusion chamber 40a is 10 ^-12
In order to maintain the atmospheric pressure, it is necessary to supply oxygen into the diffusion chamber 40a. Since the equilibrium oxygen concentration in the presence of carbon monoxide depends on carbon monoxide, oxygen may be supplied until carbon monoxide becomes close to zero. Diffusion chamber 40a through orifice 39
Since the carbon monoxide that enters inside is affected by the diffusion resistance, the supply current _i is: _i = β/2P _cp (9) where, P _cp ; is balanced by the partial pressure of carbon monoxide. Current when oxygen is near zero
_O is _O = βP _p2 (10) where P _p2 is the partial pressure of oxygen. The amount of oxygen to oxidize carbon monoxide is
As shown in FIG. 31, since it is 1/2 of the amount of carbon monoxide, _i is 1/2 of _IO . Therefore, the third
As shown in Figure 2, _i and _IO are proportional to the air-fuel ratio (A/F).

In this way, when λ<1, oxygen is supplied into the diffusion chamber 40a, and when λ>1, oxygen is supplied into the diffusion chamber 40a.
The oxygen inside the diffusion chamber 40a is
By controlling the current to 10 ^-12 atmospheres, λ can be detected. Note that the second sensor 81 determines whether the oxygen partial pressure in the diffusion chamber 40a has reached 10 ^-12 atmospheres.
In other words, since the second sensor 81 uses the reference as exhaust gas, as shown in ^FIG . is detected and the oxygen partial pressure in the diffusion chamber 40a is always maintained at 10 ^-12 atmospheres.

FIG. 33 is a basic configuration diagram corresponding to FIG. 10 showing another embodiment of the present invention, and FIG. 33 is a modification of FIG. 29. Identical operating parts are indicated by the same reference numerals, and in FIG. 33, the solid electrolyte 37 is further provided with an electrode 42 placed in the atmosphere, the electrodes 41a and 42 form a third sensor 82, and the gap between the electrodes 41a and 42 is It is designed to measure the change in electromotive force that occurs. FIG. 34 shows the output of the third sensor 82. Detecting point A (oxygen partial pressure 10 ^-12 atm), controlling the current so that the inside of the diffusion chamber 40a is always at 10 ^-12 atm, and sending oxygen into the diffusion chamber 40a,
If the output is extracted, the output shown in FIG. 35 will be obtained.

FIGS. 36 and 37 are a block diagram and a flowchart corresponding to FIGS. 13 and 20, respectively, showing other embodiments of the present invention. Note that in FIG. 36, the same parts as in FIG. 13 are indicated by the same reference numerals, and their explanation will be omitted here. In FIG. 36, the signals from the rich/lean detection sensor 58 and the O ₂ sensor 59 are not added, but are processed independently and used as control signals. That is, the signal 11b (V _L , V _R ) obtained from the output of the rich/lean detection sensor 58 via the relay circuit 55 and the control circuit 11
and signals 90a and E obtained through a processing circuit 90 of the output of the O ₂ sensor 59 are used.

Note that FIG. 36 also shows the states of change of E, V _L , and _VR according to λ. .

FIG. 37 is a flowchart of processing in the lean region. The calculation up to step 106 is the same as that shown in FIG. If the λ to be controlled is in the lean region where λ>1, look at the output E of the sensor 59, and if E>E ₀ (step 116), that is, in the rich region, reduce the correction amount w to w - Δw ( step 118), and add it to u (step 114).
In addition, when E<E ₀ , that is, in the lean region, V _L
and V _O (step 120), and when V _L > V _O , reduce w to w - Δw (step 12).
2), add to u (step 126). Also, V _L
If <V _O , w is increased to w+Δw (step 124) and added to u (step 126). Furthermore, in step 108, if λ to be controlled is λ<1, the process shifts to rich control.

FIG. 38 is a flowchart of processing in the case of a rich area. The calculation up to step 106 is the same as above, and if λ<1 and E<E ₀ (steps 208, 216), that is, in the lean region,
Increase w to w+Δw (step 218), and u
(Step 214). E>E ₀ , that is,
In the case of a rich region, V _R and V _O are compared (step 220), and if V _R <V _O , then w is reduced to w - Δw (step 222) and added to u (step 220). 226). Furthermore, if V _R >V _O , w is increased to w + Δw (step 224),
It is output in addition to u (step 226). By doing the above, the number of processing circuits can be reduced.

〔Effect of the invention〕

As explained above, according to the present invention, the air-fuel ratio can be detected in both the lean region where the excess air ratio λ is λ>1 and the rich region where λ<1, and all air-fuel ratio control is possible. In addition, it is possible to perform lean burn control and achieve significantly lower fuel efficiency.It is also useful for increasing power and reducing fuel consumption by using closed-loop control in the power zone. This has the effect that it is useful for reducing fuel consumption by controlling the air-fuel ratio appropriately during warm-up operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a control system for an automobile engine equipped with an air-fuel ratio sensor according to the present invention, FIG. 2 is a detailed block diagram of the microcomputer shown in FIG. 1, and FIG. Figures 4 and 5 are diagrams explaining the principle of the air-fuel ratio sensor in Figure 1. Figures 6 and 7 are diagrams showing the air-fuel ratio and output voltage in the lean region and rich region, respectively. FIGS. 8 and 9 are limiting current characteristic diagrams in the lean region and rich region, respectively. FIG. 10 is a basic configuration diagram showing an embodiment of the air-fuel ratio sensor of the present invention, and FIG. 11 12 is a longitudinal cross-sectional view showing one embodiment of the air-fuel ratio sensor of the present invention, FIG. 12 is a detailed structural explanatory diagram showing one embodiment of the sensor section in FIG.
Figure 3 is a configuration diagram showing an example of the overall configuration including the control circuit and signal processing circuit of the air-fuel ratio sensor of the present invention, and Figures 14 and 15 are lines explaining signal processing in the lean region and rich region, respectively. 16, 17, and 18 are circuit diagrams showing an embodiment of the relay circuit, control circuit, inverting circuit, and addition circuit of FIG. 13, respectively, and FIG. 19 is a map of λ in an automobile engine. Fig. 20 is a flowchart of λ control processing, Fig. 21 is an explanatory diagram of dead time due to exhaust lag, Fig. 22 is an explanatory diagram of the influence of dead time on control and correction method, and Fig. 23 is an explanatory diagram of the dead time due to exhaust delay.・A diagram showing the relationship between the voltage and current of the lean detection sensor,
Figure 24 is a circuit diagram showing an example of the heater control circuit in Figure 13, Figure 25 is a diagram showing the relationship between time immediately after startup and mixture concentration, and Figure 26 is A/F and ignition. FIG. 27 is a cross-sectional view showing another embodiment of the present invention; FIG. 28 is a diagram showing the relationship between λ and _B in the case of FIG. 27; FIG.
Figure 3 is a tenth diagram showing other embodiments of the present invention.
Figure 30 is the output characteristic diagram of the second sensor in Figure 29, and Figure 31 is the air-fuel ratio diagram.
The relationship diagram with CO, O ₂ %, Figure 32 is the relationship diagram with A/F in Figure 29, Figures 34, 35
The diagrams are a diagram corresponding to Figure 30 in Figure 33, a relationship diagram with λ, Figures 36 and 37.
The figures are thirteenth, each showing another embodiment of the invention.
20 is a block diagram and a flowchart corresponding to FIG. 20, and FIG. 38 is a flowchart corresponding to FIG. 37 in the case of a rich region. 7... Air-fuel ratio sensor, 11... Air-fuel ratio sensor control circuit, 12... Heater control circuit, 10... Microcomputer, 37... Solid electrolyte, 38a, 38
b, 41a, 41b, 42... Electrode, 39... Orifice, 40, 40a... Diffusion chamber, 42... Heater, 4
3...Sensor part, 44...Holder, 45...Cap, 46...Atmospheric chamber, 47...Stopper, 48...Holder, 49...Cover, 50...Vent hole, 51...Exhaust chamber, 52...Cover, 53...Hole, 54... Ceramic coating, 55... Relay circuit, 56... Inversion circuit, 57... Addition circuit, 58, 80... Rich/Lean detection sensor, 59, 81, 82... O ₂ sensor,
90...processing circuit.

Claims (1)

[Scope of Claims] 1. A solid electrolyte having oxygen ion conductivity is provided with a first and second electrode pair, and the first electrode pair is in exhaust gas and has one electrode side in contact with the exhaust gas. A diffusion resistor is provided, and at least the first electrode pair and a means for reversing the direction of a predetermined current flowing between the two electrodes when detecting a lean region and detecting a rich region of the air-fuel ratio;
means for outputting an electromotive force generated in the first electrode pair when the electrodes are passed through the electrode, and a rich lean detection sensor section is configured; (including the atmosphere), the other electrode is in contact with exhaust gas, and at least the second electrode pair and a means for outputting an electromotive force generated between the electrodes.
It constitutes an O ₂ sensor section, and when detecting an air-fuel ratio in a lean region, the output of the rich/lean detection sensor section and the output of the O ₂ sensor section are combined, and when detecting an air-fuel ratio in a rich region, An air-fuel ratio sensor comprising: a signal processing system that detects an air-fuel ratio based on a combination of the output of the rich/lean detection sensor section and the inverted output of the O ₂ sensor section. 2. The solid electrolyte has a heating heater printed on its surface, and the heater is controlled to turn on and off the current applied so that the deviation between the actually measured temperature and the optimum temperature is zero. The air-fuel ratio sensor according to item 1. 3. The air-fuel ratio sensor according to claim 1 or 2, wherein the diffusion resistor is constituted by a diffusion chamber having an orifice for introducing exhaust gas. 4. The predetermined current flowing through the first electrode pair has a current value variable by a current control means, and the current control means outputs a current value flowing between both electrodes of the first electrode pair from a computer. The air-fuel ratio sensor according to claim 1, wherein the air-fuel ratio sensor is configured to control the current to match a set value of the current depending on the excess air ratio to be controlled. 5. The signal processing system includes a conversion circuit that converts the output electromotive force from the rich/lean detection sensor section into a signal of 0 and 1, and compares the output electromotive force from the O ₂ sensor section with a predetermined slice level. When detecting the air-fuel ratio in the lean region, the signal is output as is, and when detecting the air-fuel ratio in the rich region, the output signal 0, 1 of the O ₂ sensor section is converted into a signal of 0, 1. Claim 1, comprising: an inverting circuit that inverts and outputs the inverted output; and an adding circuit that adds the output of the converting circuit and the output of the inverting circuit.
The air-fuel ratio sensor according to item 1 or 2 or 3 or 4.