JPS5967455A - Air/fuel ratio sensor - Google Patents

Abstract

PURPOSE:To enable every possible air/fuel ratio control by providing first and second electrodes on both sides of a solid electrolyte on the exhaust side and third and fourth electrodes on the exhaust and atmospheric side thereof while a diffusion chamber is provided with an orifice on the exhaust side and the electrode side of the first and second electrodes. CONSTITUTION:A platinum electrodes 38a and 38b are provided on both sides of a solid electrolyte 37 and a diffusion chamber 40 is provided with an orifice 39 on the side of the electrode 38b. Current I flowing between I between the electrodes 38a and 38b are made switchable from the normal to opposite direction vice versa. An oridinary oxygen sensor is provided with an electrode 41a on the atmospheric side and an electrode 41b on the exhaust side additionally to prevent changes in the electromotive force when lambda=1.0 (lambda: excessive air rate). A heater 42 is printed on the solid electrolyte 37 to heat the solid electrolyte 37 up to a high temperature. Then, a rich/lean detection sensor 58 is provided as partly composed the electrodes 38a and 38b and an O2 sensor 59 as partly composed of the electrodes 41a and 41b.

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, this type of conventional air-fuel ratio sensor can only measure the air-fuel ratio in the lean region and cannot measure the air-fuel ratio in the rich region, making it unsatisfactory for use in controlling the air-fuel ratio of automobile engines. Ta. Unfortunately, because the standard oxygen concentration was the atmospheric oxygen concentration, the drawback was that it was impossible to reduce the capacity of the heater used to maintain the solid electrolyte at a high temperature.

[Purpose of the invention]

The present invention has been made in view of the above, and its purpose is to be able to detect the air-fuel ratio whether the excess air ratio λ is λ>1 or λ<1, and to enable all air-fuel ratio control. An object of the present invention is to provide an air-fuel ratio sensor that can perform

[Summary of the invention]

The present invention is characterized by a solid electrolyte and a first tube provided on both sides of the solid electrolyte on the exhaust side. a second electrode, and a third electrode provided on the exhaust side and the atmosphere side of the solid electrolyte, respectively. a fourth electrode; and a diffusion chamber having an orifice opening to the exhaust gas provided on the exhaust side electrode of the second electrode. The part consisting of the second electrode is operated as a rich/lean detection sensor, and the part consisting of the second electrode is operated as a rich/lean detection sensor.
The portion consisting of the fourth electrode is operated as the 02 sensor, and the portion consisting of the 4th electrode is operated as the 02 sensor. a reversing means for reversing the direction of the current flowing between the second electrodes between the rich region and the one-in region; a current control means for controlling the current value of the current flowing between the second electrodes to a predetermined current value; and a processing means for processing the air-fuel ratio of the exhaust gas to be measured and outputting an output according to the air-fuel ratio of the exhaust gas to be measured.

[Embodiments of the invention]

The present invention will be described below with reference to FIGS. 1, 2, 10 to 13, 16 to 18, 20, 24, 27, 29, 33, 36. The embodiment shown in FIGS. 38 to 38 and FIGS. 3 to 9.

Fig. 14, Fig. 15, Fig. 19, Fig. 21 to Fig. 23,
Fig. 25, Fig. 26, Fig. 28, Fig. 30 to Fig. 32,
This will be explained in detail using FIGS. 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, 7 is an air-fuel ratio sensor according to the present invention, 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, and 13 is a combustion chamber.
(1) The air-fuel ratio is detected using the air-fuel ratio sensor 7 which can detect the air-fuel ratio over a wide range (λ>1), and the air-fuel ratio is controlled. That is, when the air-fuel ratio to be controlled is determined by the microcomputer 10 based on the rotational speed, load, water temperature, etc., it is output to the injection valve 3 and the slot actuator 4, and the intake air amount is detected by the intake air amount detector 2. closed-loop control.

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,
The signal is input to the microcomputer 10 for closed loop control. Note that the air-fuel ratio sensor 7 must be heated to a high temperature due to the characteristics of the solid electrolyte used, so a heater drive circuit 12 is provided.

FIG. 2 is a detailed configuration diagram of the microcomputer 10 shown in FIG. 1. The analog human input signal is the air amount signal AF from the hot wire intake air amount detector 27A).

The water temperature signal T' from the water temperature sensor 6, the throttle opening signal θ from the throttle actuator 4, etc. These signals are input to the multiplexer 30, and each signal is selected in a time-sharing manner and sent to the AD converter 31. Here it is converted into a digital signal. In addition, information input as an on-off signal includes the air-fuel ratio sensor 7
There is a signal 11b from the control circuit 11, which is treated as a 1-bit digital signal. Furthermore, pulse train signals CRP and CPP from the crank angle sensor 8 are also input. 32 is a ROM, 33 is a CPU, and the CPU 33 is
It is a processing central unit that performs digital arithmetic processing, and the ROM 32 is a storage element that stores control programs and fixed data. RAM 34 is a readable and writable storage element. The I10 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 actuator 4, the ignition coil 9, and the heater drive circuit of the air-fuel ratio sensor 7. 12 and the 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 the Ricci-Rino double head region, and the principle thereof will be briefly explained. FIG. 3 is an explanatory diagram of the principle of the air-fuel ratio sensor 7, in which FIG. 3(a) shows the detection principle in the IJ-low range, and FIG. 3(1)) shows the detection principle in the rich range. As shown in FIG. 3, positive and negative electrodes 33a and 38b are provided on both sides of the solid electrolyte 37, and a diffusion chamber 40 is further provided via an orifice 39 that serves as a gas diffusion resistance. When detecting the air-fuel ratio in the lean region, as shown in FIG. 3(a), a voltage is applied so that an electric current flows in the direction shown, using the electrode 38a as an anode and the electrode 38b as a cathode. At this time, oxygen proportional to the current (2) passes through the solid electrolyte 37 and is pumped out from the diffusion chamber 40. Also, when detecting the air-fuel ratio in the rich region,
As shown in FIG. 3(b), the electrode 38a is a cathode, and the electrode 38a is a cathode.
Using 8b as an anode, a voltage is applied so as to cause the current to flow in the opposite direction to that described above. At this time, oxygen flows into the diffusion chamber 40 from the exhaust side. After that, carbon monoxide (CO) that has flowed in through the orifice 39 reacts with the carbon monoxide (CO) in the diffusion chamber 40 as shown in the following equation.

In this way, in both FIGS. 3(a) and 3(b), a state is created in which the oxygen partial pressure inside the diffusion chamber 40 is extremely low (1 o - 12 atm), and the inside of the diffusion chamber 40 is always kept at a stoichiometric pressure (λ=1
．． When the exhaust state is maintained at 0), 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 explaining the principle of detection in the beam area.

The amount G+x of oxygen that enters the diffusion chamber 40 via the georifice 39 due to gas diffusion is the concentration of oxygen in the exhaust gas N t
Proportional to e. That is, G IK = ' N le
.+.(2) where, K: constant Therefore, as shown in FIG. 4(a), the amount of oxygen entering the diffusion chamber 40 by diffusion increases as the excess air ratio λ increases. Furthermore, when the current ■ is applied as shown in FIG. 3(a), the current 1 [11 in FIG. 4(a)].

1-2] is pumped out from the diffusion chamber 40. In other words, when a current of ■ is passed, λ〈λ1
The amount of oxygen pumped out is larger than that in Figure 4 (C
), when the oxygen partial pressure inside the diffusion chamber 40 is small, p
(10-12 atmospheres), and as in a normal oxygen sensor, an electromotive force of about 1V is output as shown in FIG. 4(b).

In addition, in the region of λ - λ1, the amount of oxygen that enters the diffusion chamber 40 by diffusion is greater than the amount of oxygen that is pumped out, so 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, the current ■1 causes a change in the electromotive force when λ=λ. Also, at a current of 1°, λ=λ2
A change in electromotive force occurs when .

FIG. 5 is an explanatory diagram of the detection principle in a rich region.

In the rich region, λ is detected based on the amount of carbon monoxide that diffuses into the diffusion chamber 40. Nowadays, Figure 3 (1
)), a solid electrolyte 3 is placed inside the diffusion chamber 40.
Oxygen is delivered via 7. When an amount of oxygen proportional to 1 is sent into the diffusion chamber 40, when λ>λ1, the diffusion chamber 4
The amount of carbon monoxide that falls within 0 is smaller than 1 < , and the amount of oxygen consumed by the reaction is smaller, as shown in equation (1).
As shown in FIG. 5(d), a large amount of oxygen is retained in the diffusion chamber 40, and the oxygen partial pressure in the diffusion chamber 40 is higher than the oxygen partial pressure in the exhaust gas in the rich region. An oxygen partial pressure difference occurs on both sides, and an electromotive force is generated as shown in FIG. 5(b). Further, at λ less λl, 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. 5(C). As shown in FIG. 5(b), the oxygen partial pressure in the diffusion chamber 40 becomes smaller and becomes equal to the oxygen partial pressure in the exhaust gas.
As shown in , no electromotive force is generated. Furthermore, if the current value is changed to I2, λ2 will be detected.

As described above, by changing the direction of the current flowing through the solid electrolyte 37, the air-fuel ratio can be detected over a wide range from the lean region to the rich region.

The results measured as described above are shown in FIGS. 6 and 7. Fig. 6 In the case of the beam in the 1-in region, when I = 2 mA, A/F = 15 (A: air amount, F
; fuel amount), and in the case of I = 4 mA, the electromotive force changes when A/F = 16, as shown by the 5 curve. However, due to the oxygen partial pressure difference, the electromotive force changes even at λ-1 and 0, resulting in a two-position change. Countermeasures against this will be described later.

Figure 7 shows the case in the rich region, as in the 'v c+d curve, when I=2mA, A/F=14.3, and I=
In the case of 4 mA, the starting force changes at A/F'=13.6. At this time, the electromotive force still changes around λ-1,0, and countermeasures for this will be described later.

The above method is to keep the current ■ constant and observe the change in the electromotive force, but the A/F
may be detected. FIGS. 8 and 9 are diagrams showing measurement examples in that case. FIG. 8 shows the case in the beam range, and when the voltage (2) is changed, a limiting current Io2 proportional to the oxygen concentration (%) is obtained. Figure 8(a) shows the relationship between voltage and limiting current using oxygen concentration as a parameter, and curves e-g represent oxygen concentrations of 2 and 4.6, respectively.
Indicates the case of the person in charge. FIG. 8(b) shows the oxygen concentration and limit current when the voltage is kept constant at 0.5 V, and it can be seen that a current Io proportional to the oxygen concentration is output.

Here, keeping the voltage applied to the solid electrolyte 37 at 0.5 V means that the oxygen partial pressure in the diffusion chamber 40 is always kept at 10 V.
It is controlled to maintain the pressure at -12 atmospheres (stoichiometry, exhaust state of λ-1,0). In other words, when the oxygen concentration increases and the amount of oxygen entering the diffusion chamber 40 increases, the current 1
Increase the amount of oxygen, pump out the amount of oxygen corresponding to the increased amount, and maintain the oxygen partial pressure at 10-12 atmospheres. That is, when the oxygen concentration in the exhaust gas increases, the current 1o2 increases.

FIG. 9 shows the measurement results in the rich region. FIG. 9(a) shows the relationship between voltage and limiting current using carbon monoxide concentration (ch) as a parameter, and curves h-J show the cases where carbon monoxide concentration is 2 and 3.4, respectively. 9th
Figure (b) 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 raise the oxygen partial pressure to a high value <L, V=0.5V. It always tries to maintain the partial pressure difference. Therefore, as shown in FIG. 9(1)), as the -carbon oxide concentration increases, the limiting current Ico 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 1 flowing between the electrodes 38a and 38b is switched between the positive direction and the rain direction. In addition, as shown in Figures 6 and 7,
In order to avoid a change in electromotive force when λ=j, O, an electrode 41.3 on the atmosphere side and an electrode 411 on the exhaust side are added to a normal oxygen sensor whose electromotive force changes at λ-1, 0. ]
(A workaround will be described later.)
. Further, a heater 42 for heating the solid electrolyte 37 to a high temperature is printed on the solid electrolyte 37''. Reference numerals 58 and 59 indicate a rich/lean detection sensor consisting of electrodes 38a and 381), and a 02 sensor consisting of electrodes 41a and 41b, respectively.

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 type keratin, and the solid electrolyte 37 includes each electrode 3 as shown in FIG.
8a, 38b, 41a, 41b and a heater 42 are added to form a sensor section 43. The sensor section 43 is inserted into the center of a ceramic holder 44. 45 is a cap, camp 45 has holder 4
A ventilation hole 45a is provided to introduce the atmosphere to an atmospheric chamber 46 at the center of the air chamber 4. Reference numeral 47 is a stopper, which is provided in the center hole 5 in the senna part 43.
3 (see FIG. 12), and is used to fix the sensor section 43. The stopper 4 near 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. That's how it is. Note that the cap 49 is made of ceramic to prevent heat radiation due to radiation from the heater 42 (see FIG. 12). The entire body is covered with an external cover 52 which is intended to be attached to the exhaust pipe, and the cup 52 is fixed to the holder 44 with a caulked portion 53.

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), and (C) is a A right side view, (d) is a sectional view taken along the line A-A in (a). The sensor section 43 is mainly composed of a rectangular solid electrolyte 37, and one side has an electrode 38a for detecting the air-fuel ratio in the rich/lean region and a heater 42, as shown in FIG. 12(l). is printed as shown in the figure, and the other side has an electrode 381 for detecting the air-fuel ratio in the rich/lean region, as shown in (C).
] and the atmosphere-side electrode 41a and exhaust-side electrode 41b for detecting the electromotive force at λ21,0 are printed. Furthermore, a hole 53 into which a stopper 47 shown in FIG. 11 for fixing the sensor section 43 is inserted is provided. Note that the heater 42
The part where is printed is as shown in Fig. 12(d),
A ceramic coating 54 is applied to the heater 42 to prevent it from peeling off.

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 the air-fuel ratio sensor 7 is attached to the exhaust pipe 14. 12 is a control circuit for the heater 42; 55 is an electrode 3;
A relay circuit 11 reverses the direction of the current flowing between the electrodes 38a and 38b, and 11 makes the current flowing between the electrodes 38a and 38b a constant current, and processes the output signal to set VR in the rich region and VL in the lean region. A control circuit 56 outputs the electrode 41a when λ-1,0.

an inverting circuit that outputs an electromotive force signal 56a (Oz) generated between 41b and a signal 56b (02) obtained by inverting it;
7 performs calculations of (VL +02) and (VR+O□), and generates signals 57a corresponding thereto.

571). As a result, the 6th
The two-position problem explained in FIGS. 7 and 7 can be avoided.

Next, the concept of signal processing will be explained using FIGS. 1.4 and 15. FIG. 14 is an explanatory diagram of signal processing in the beam area. (a) is the set current I(lla) at a certain value
This is the waveform of the output signal VL (11, 1)) from the rich/lean detection sensor 58 when input to the control circuit 11. As mentioned above, this signal Vr changes in magnitude at a certain air-fuel ratio in the lean region, but furthermore, when λ=1
It changes even at 0. (1)) is the waveform of the signal 56a outputted from the inverting circuit 56 and changing at λ21.0.

(C) is the signal V1. of (a). and (b) signal 56a (
0□) in an adder circuit 57, a signal 57 a (V
L +02 ) waveform. The signal 57a obtained in this way does not change except for the air-fuel ratio in the lean region, thereby making it possible to solve the two-position problem described above. Note that the signal V r is the electrode 38
The signal 56a is output from the rich/lean detection sensor 58 consisting of parts a and 38b, and the signal 56a is output from the electrodes 41a and -41b.
The signal is output from the 02 sensor 59 consisting of the section .

FIG. 15 is a diagram illustrating signal processing in a rich region. (
a) is the waveform of the signal VR, in this case, the relay circuit 55
The direction in which the current I flows is reversed to obtain the signal VR. (I)) This is the waveform of a signal 56b obtained by inverting the signal 56a from the O2 sensor 59 at the slice level by the inverting circuit 56.

A signal 571) obtained by adding these two signals in an adder circuit 57
The waveform of is shown in (c). In this case as well, the two-position problem is solved as above.

FIG. 16 is a specific circuit configuration diagram of the relay circuit 55 and control circuit 11 shown in FIG. 13. The control circuit 11 includes a circuit 11A that supplies a constant set current Io to the rich/lean detection sensor 58, and a circuit 11A that processes the signal (electromotive force) from the sensor 58 into an on/off signal that changes at a slice level and generates a signal VL.
, and a circuit 11B that outputs V a. The circuit 17A inputs the analog value 11a of the current 1 setting signal from the computer 1° (see Figure 1) outputted from the DA converter, and inputs the analog value 11a of the current 1 setting signal outputted from the DA converter, and a voltage proportional to the current d generated by the resistor 6o. is input to the comparator 61, the output of the comparator 61 operates the transistor 62, and the transistor 63 thereby controls the current.

The circuit 11B converts the electromotive force, which is the output signal from the rich/lean detection sensor 58, into a signal 111 of the tube regulator 64fO,1 (VL).

VR). The relay circuit 55 is connected to the computer 1
Rich control is performed by control signal 55a from 0.

The direction of the current flowing through the sensor 58 is switched between positive and reverse depending on the lean control.

FIG. 17 is a circuit diagram showing an embodiment of the inversion circuit 56 of FIG. 13. Detecting the electromotive force at λ-1,Q02
The signal from the sensor 59 is input to the comparator V-Taro 5 and compared with the slice level 8, which outputs the o2 signal 56a, which is an on/off signal.Furthermore, this signal is inverted by the transistor 66, and the l. Ranjistaro 6 to 0
2 signal 561) is also output.

FIG. 18 is a circuit diagram showing an embodiment of the adder circuit 57 in FIG. 1. This circuit adds the signal VR and the 0 signal 561) to generate the signal 571], the signal VL and the 02 signal 56
a and outputs a signal 571).
It consists of two sets of circuits shown in the figure.

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 based on this map, the setting current signal 11a is applied to the circuit 11A.
Output to.

The 20th example is flowchart 1 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, the fuel amount Or is calculated, and the valve opening time U of the injection valve 3 (see FIG. 1) is calculated. Next, set current 1 is determined. If the λ to be controlled is in the lean region where λ>1, then (V L +
02) Check whether the signal 57a 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, in the rich region of λ<1, the opposite is true, (V
11+02) Check whether signal 571] is on or off,
If it is on, increase W; if it is off, reduce W and add it 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 is the mixture in combustion chamber 1
3, which means the time when the combusted exhaust gas passes through the exhaust pipe 14 and reaches the air-fuel ratio sensor 7. 21st
Figure (2) is a diagram showing the relationship between the number of rotations and the dead time t1. As the number of rotations increases, the dead time t1 decreases.

FIG. 12(1)) is a diagram showing the relationship between load and tl, in which 11 decreases as the load increases. In other words, tl changes two-dimensionally depending on the rotational speed and load.

Next, a method for correcting the influence of dead time t1 on control will be explained with reference to FIG. If you try to change λ according to instructions from the computer 10, if the amount of fuel decreases due to the operation of the injector 3 as shown in FIG. 22(a), and the set current ( 1) Assuming that changes in I1 are made at the same time, in the lean region, the ability to pump out oxygen from the diffusion chamber 40 increases due to the increase in current ■, and even though there is no change in the oxygen concentration in the exhaust gas, the oxygen is diffused. During the time 1a until the oxygen partial pressure in the chamber 40 decreases, the interior of the diffusion chamber 40 becomes more diluted than the stoichiometric state, and the exhaust gas reaches the sensor 7, as shown in FIG. 22(C). A high electromotive force is generated from the sensor 7, resulting in an uncontrollable time period. However, if the process is changed after the exhaust gas reaches the sensor 7, this problem will not occur. As shown in Figure (d), the set current (2
) The above problem can be solved by changing I2 with a delay of the dead time t8 due to exhaust delay such as I2. The same is true when increasing the amount of fuel, with a delay of tb and 12
to prevent problems from occurring. Note that this dead time varies depending on the rotational speed and load as shown in FIG. 21, so it is corrected according to FIG. 21.

Furthermore, it goes without saying that the dead time t1 may be measured and corrected using the processor 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.

Still, when the sensor temperature changes, the output changes. Next, a method for controlling the sensor temperature will be explained.

FIG. 23(a) is a diagram showing the relationship between voltage and current of the rich/lean detection sensor 58 using temperature as a parameter.
The curves k-rη are sensor temperatures Tl, T2 . T3
(However, this is the relationship in the case of Tl>T2>'d). 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 FIG. 23(a), the higher the sensor temperature, the lower the voltage of the limiting current 11 will flow. In the case of temperature T3, the control signal is ΔVT3 with VP(T3) as the peak value.
Varies between. This situation is shown in FIG. 23 (l). As can be seen from FIG. 23(1)), the sensor temperature T+1'], '21'1. ”3, the control signal peak values VP(Tl), VP(T2), VP(T
3) changes. In other words, by reading this Vp, you can tell whether the temperature is appropriate. For example, if T2 is the optimal temperature, T1 is too high and Vp decreases, and T3 is too low and Vp increases. Since this Vp also changes depending on the current T, VP must be mapped according to the set current 1. Note that the slice level at this time is (vp + Vn)/2 C to 1B, as determined by (see FIG. 23 (1))), and the deviation can correspond to a change in Vp.

FIG. 24 is a circuit diagram showing an embodiment of the heater control circuit 12 of FIG. 13. The above-mentioned actually measured Vp and the optimum Vp are compared by a comparator 67, and an on-off duty signal corresponding to the deviation amount is supplied to the transistor 68,
The configuration is such that the output IH of the l-range star 8 controls a relay switch 69 that turns on and off the shift 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.

FIG. 25(a) is a diagram showing the relationship between time immediately after startup and mixture concentration using water temperature as a parameter.

The 0 curves show the relationships when the water temperatures are Tl and T2, respectively. Immediately after starting, the mixture is concentrated, and as time passes, it becomes thinner, and as the water temperature rises, it becomes thinner. In other words, in the warm-up state, the appropriate A is determined by the cooling water temperature.
If /F is given, it will be possible to drive 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 is possible to control a rich mixture immediately after starting.

If the relationship between water temperature and A/F shown in FIG. 25(b) is recorded in the computer 10, operation can be performed according to this function during warm-up. FIG. 25(c) is a control block diagram at this time. The signal from the water temperature sensor 6 is input to the computer 10, the A/F is determined from the function showing the relationship shown in FIG. 25(b), and the signal 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. be able to.

Although it is still necessary to control the ignition timing based on changes in the air-fuel ratio, it can also be useful for that purpose. Second
Figure 6 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, since load is also a parameter for ignition timing, ignition timing must be controlled using a three-dimensional map of A/F, rotation speed, and load, but it is possible to easily realize control using A/F. can.

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. 10, there is also a diffusion chamber A including an electrode 41a. Oxygen partial pressure in diffusion chambers A and B P A + P B
is -P A -P M+β■9-βIB
...(3) PR=PA-βIB
(4) Here, β; constant ■A; current 1B flowing between electrodes 41a and 4Lb; current PM flowing between electrodes 38a and 38b; partial pressure of oxygen in exhaust gas. From equations (3) and (4), P B = P M + βIA-2βT-B
...(5) holds true. Therefore, IB, which becomes PB-0, becomes PMgo01, that is, excess air ratio λ-
1, but if 1>0, as shown in Figure 28, I
It will not be B20. In the Lynch region of λ〈1, the reaction of C02CO+1/202...(7) progresses, and if this reaction is balanced in diffusion chamber A, the oxygen in diffusion chamber A will be consumed in the oxidation of carbonic acid monoxide. be done. 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, and therefore the amount of oxygen in the diffusion chamber A decreases. That is, oxygen becomes zero at the 0 point in FIG. 28, and a signal corresponding to λ can be obtained.

Further, in the configuration shown in FIG. 27, it is also possible to control 13 so that I Tl is constant and PR becomes zero. In this case, from equation (5), the following is obtained, and as PM increases, IA 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 4 of FIG.
0 as a diffusion chamber 40a containing 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 is the first sensor;
81 indicates a second sensor. FIG. 30 is an output characteristic diagram of the second sensor 81. Oxygen in the diffusion chamber 40a is IQ-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 oxide is influenced by -carbon oxide, oxygen may be supplied until -carbon oxide becomes close to zero. orifice 39
Since the carbon monoxide that enters the diffusion chamber 40a through it is affected by the diffusion resistance, the supply current {circle around (2)} is balanced by the partial pressure of carbon oxide. The current 10 when the oxygen is brought close to zero is To-βPO3... where Po is the partial pressure of oxygen. -The amount of oxygen to oxidize carbon oxide is the 31st
As shown in the figure, -1/2 of the amount of carbon oxide, so ■
1 is 1/2 of 10. As shown in Fig. 32, I + T, O is the air-fuel ratio (A/Ii
”).

In this way, when λ<1, oxygen is supplied into the diffusion chamber 40a, and when λ>1, oxygen is pumped out from inside the diffusion chamber 40a, so that the oxygen inside the diffusion chamber 4Oa reaches 10-12 atmospheres. By controlling the current so that λ can be detected. Note that the oxygen partial pressure in the diffusion chamber 40a is 10-1
The second sensor 81 determines whether the pressure is 2 atmospheres.
done by.

In other words, since the second sensor 81 uses the exhaust gas as a reference, 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, and the electrodes 41a and 42 form a third sensor 82.
The electromotive force change generated between the electrodes 41a and 42 is measured. FIG. 34 shows the output of the third cell 82.

Detecting point A (oxygen partial pressure 10-12 atm), the diffusion chamber 4
If the current 1 is controlled so that the pressure inside Oa is always to -12 atmospheres and oxygen is sent into or pumped out into the diffusion chamber 40a, the output shown in FIG. 35 can 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. 36th
In the figure, the signals from the rich/lean detection sensor 58 and the 02 sensor 59 are not added, but are processed independently and used as control signals. That is, the relay circuit 55 for the output of the rich/lean detection sensor 58 and the control circuit 1
A signal 11t) (VL, VR) obtained through 1 and a signal 90 obtained through a processing circuit 90 of the output of the 0□ sensor 59.
It is recommended to use a■.

In addition, FIG. 36 also shows the changing states of E, VL, and VR according to λ.

FIG. 37 is a flowchart of processing in the case of a line area. The calculation up to step 106 is the same as in FIG. 20. When λ is in the lean region where λ>1 after control,
Looking at the output E of the sensor 59, E>Eo' (step 11
6), that is, in the case of a rich region, the correction amount W is W - ΔW
(Step 118) and add it to U (Step 114).

IE (E, that is, in the lean region, V L
, l! :'V o comparison 17 (step 120), V
+, )Vo, W is decreased by W-ΔW (step 122) and added to U (step 12G). Also, V
If [,<VO, W is increased to W+ΔW (step 124) and added to u (step 126). Further, in step 108, if the desired 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, with λ<1 and E<E. (Steps 208, 216),
That is, in the case of the lean region, W is increased to W+ΔW (step 218) and added to U (step 214).

If E>Eo, that is, in a rich region, VR and Vo are compared (step 22o), where VR(V
oO, reduce W to W-ΔW (step 222
), are added to U (step 226). Also, VR>V
o, increase W to W+ΔW (step 224
), and output in addition to u (step 226).

By doing the following, 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 even in the range where the excess air ratio λ is λ>1 or in the rich region where λ<1, and all air-fuel ratio control is possible. It also enables lean burn control and achieves a significant reduction in fuel consumption. 1) It is useful for increasing power and reducing fuel consumption by using closed loop control in the power zone, Even during warm-up operation immediately after, it is useful for controlling the air-fuel ratio appropriately and reducing fuel consumption.

[Brief explanation of the drawing]

FIG. 1 shows the components of 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 configuration 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 and rich regions, respectively. FIG. 8 and FIG. 9 are limiting current characteristic diagrams in the lean region and rich region, respectively, and FIG. 10 is a basic configuration diagram showing an embodiment of the air-fuel ratio sensor of the present invention.
FIG. 11 is a longitudinal cross-sectional view showing an embodiment of the air-fuel ratio sensor of the present invention, FIG. 12 is a detailed structural explanatory diagram showing an embodiment of the sensor portion of FIG. 11, and FIG. 13 is a diagram showing the air-fuel ratio sensor of the present invention. FIGS. 14 and 15 are diagrams illustrating signal processing in the lean region and rich region, respectively, and FIG. 17th
18 are circuit diagrams showing one embodiment of the relay circuit, control circuit 2 inverting circuit, and addition circuit of FIG. 13, respectively.
Figure 9 is a map of λ in an automobile engine, Figure 20 is a flowchart of λ control processing, Figure 21 is an explanatory diagram of dead time due to exhaust lag, and Figure 22 shows the influence of dead time on control and correction method. The explanatory diagram, Figure 23, shows the rich
A diagram showing the relationship between the voltage and current of the IJ-on detection sensor,
Fig. 24 is a circuit diagram showing an example of the heater control circuit shown in Fig. 13, Fig. 25 is a diagram showing the relationship between time immediately after startup and mixture concentration, and Fig. 26 is a diagram showing the relationship between A/F and ignition. 27 is a sectional view showing another embodiment of the present invention; FIG. 28 is a diagram showing the relationship between λ and IB in the case of FIG. 27; FIGS. 29 and 33 The figures are basic configuration diagrams corresponding to Fig. 10 showing other embodiments of the present invention, and Fig. 30 is a basic configuration diagram corresponding to Fig. 29.
The output characteristic diagram of the second sensor shown in Fig. 31 shows the air-fuel ratio and C
o, 02%, Figure 32 is a relationship diagram between A/F and 1 in Figure 29, Figures 34 and 35 are diagrams corresponding to Figure 30 in Figure 33, respectively. , λ and 1; FIGS. 36, 37 are block diagrams corresponding to FIGS. 13 and 20 showing other embodiments of the present invention, and flowchart 1-1, FIG. 38. is a flowchart corresponding to FIG. 37 in the case of a rich area. 7... Air-fuel ratio sensor, 11... Air-fuel ratio sensor control circuit, 12... Heater control circuit, 10... Microcomputer, 37... Solid electrolyte, 38 a,
38b. 41a, 41b, 42...electrode, 39...orinois, 40.40 meter...diffusion chamber, 42...heater, 43
...Sensor part, 44...Holder, 45...Cap, 46...Atmospheric chamber, 47...Stopper, 48...
...Porter, 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 leaf detection sensor, 59,81.8
2...02 sensor, 90...processing circuit. 336 Chemical 2 Figure 3 Figure 3 (Kyu) C Ku9 θ group 8th θz ('/-) 7th supply voltage T < V) CO (y-zi half 10 Figure not used Figure 7 Potato /Z day (d -,) 74th solid) ic) < 1.0 /ea-n ts
Mouth P-K It 7,0 /eLx Detection 20 (¥1 Fig. 24 椪擾病? Fig. 25 (a,) Otsu (pulverization) Fig. 26 A/F Fig. 27 Fig. 28 Half 2' l Zuban Sazo, O-+2 appeal $31 figure 11 $330 Kasa 34 figure completed 35 area figure 36 I 3q mouth 3z figure

Claims (1)

[Claims] 1. A solid electrolyte, and a first electrode provided on both sides of the solid electrolyte on the exhaust side. a second electrode, a third and fourth electrode provided on the exhaust side and the atmosphere side of the solid electrolyte, respectively; a diffusion chamber provided on one side of the second electrode and having an orifice opening to the exhaust gas; The portion consisting of the second electrode is operated as a rich/lean detection sensor, and the third electrode is operated as a rich/lean detection sensor. The portion consisting of the fourth electrode is operated as an 02 sensor, and the first,
reversing means for reversing the direction of the current flowing between the second electrodes between the rich region and the one region; current controlling means for controlling the current value of the current flowing between the first and second electrodes to a predetermined current value; and processing means for inputting and processing the output electromotive force from the rich/lean detection sensor and the output electromotive force from the 02 sensor, respectively, and sending out an output according to the air-fuel ratio of the exhaust gas to be measured. An air-fuel ratio sensor featuring: 2. The solid electrolyte has a heating heater printed on its surface, and the heater is controlled to turn on and off the current flowing so that the deviation between the actually measured temperature and the optimum temperature is zero. The air-fuel ratio sensor according to range 1. 3. The air-fuel ratio according to claim 1 or 2, wherein the reversing means is configured to change the direction of the current to positive or reverse depending on rich region control or lean region control. sensor. 4° The current control means is configured to control the first current control means. Claim 1 or 2 is characterized in that the current value of the current flowing between the second electrodes is controlled so as to match a current setting value outputted from a computer according to the excess air ratio to be controlled. The air-fuel ratio sensor according to item 1 or 3. 5. The processing means includes a conversion means for converting the output electromotive force from the rich/lean detection sensor into a signal of 0.1;
The output electromotive force from the 0□ sensor is compared with a predetermined slice level and converted into a 0.1 signal, the signal is output as is in the dark area, and the signal is inverted in the rich area. and an adder circuit that adds the output of the converting means and the output of the inverting circuit, according to claim 1, 2, 3, or 4. air fuel ratio sensor.