JPS6199852A - Air-fuel ratio detector - Google Patents

Abstract

PURPOSE:To improve the interchangeability with circuits by providing a variable resistor which corrects the variance in the resistance value of a diffused resistor and electrode and a variable resistor which corrects the variance in the resistance value of an added heater within an external circuit including a driving circuit. CONSTITUTION:The constant voltage or constant current from a circuit 29 in a circuit board M is supplied to the heater 3. The compensating resistor 27 for the heater is provided on the S part side of a connector C part in the mid-way in the case of connecting a sensor S part and the M part. The variance of the resistance value of the heater 3 can be compensated on the S part side by regulating the resistance value of the resistor 27. The specified voltage is supplied from the terminals 33, 34 in the circuit 30 to a solid electrolyte 4 and the current value flowing to the electrolyte 4 is detected by the terminals 32, 33 as the voltage value at both terminals of the resistor 28 for compensating the solid electrolyte. The variance of the electrolyte 4 is compensatable by regulating the resistance value of the resistor 28. The interchangeability with the circuits is thus improved without the need for compensating the variance on the circuit side.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an air-fuel ratio detector, and particularly to an air-fuel ratio detector suitable for use in a combustor or the like.

[Background of the invention]

Conventionally, manufacturing variations in the resistance values of diffusion resistors and electrodes of air-fuel ratio detectors have been solved by changing the resistance values provided in external circuits, such as microcomputers, as shown in Japanese Unexamined Patent Publication No. 59-34432. I was adjusting it by adjusting it.

However, when such a correction method is adopted, the circuit and the detector must be adjusted together, making the air-fuel ratio detector incompatible, which is extremely inconvenient in terms of mass production, cost, and maintenance. was there.

[Purpose of the invention]

An object of the present invention is to provide an air-fuel ratio detector that has improved compatibility and can further reduce maintenance costs and costs.

[Summary of the invention]

The present invention provides a first variable resistor for correcting variations in resistance values of a diffusion resistor and an electrode of an air-fuel ratio detector, and a first variable resistor for correcting variations in resistance value of a heater added to an air-fuel ratio detector. The second variable resistor is provided in an external circuit including a drive circuit of the air-fuel ratio detector.

[Embodiments of the invention]

FIG. 1 is a sectional view showing an embodiment of a sensor main body 1 of an air-fuel ratio detector according to the present invention.

In FIG. 1, 2 is a protective tube, 3 is a heater, 4 is a solid electrolyte, 5 is a washer, 6 is a stopper, 7 and 8 are washers, 9 is a filler, 10 is a spacer, 11 is a washer, 12
is a wire mesh, 13 is a metal case, 14 is a metal pipe, 15 is a coil spring, 16 is a metal case, 17 and 18.19
20 is an insulator, 20 is a disc spring, 21 is a grommet, 22 is a lead wire for a heater, and 23 is a lead wire for a solid electrolyte.

The sensor main body having such a structure is attached to the exhaust pipe of the combustor through the plug body 6. The solid electrolyte 4 is heated and activated by the heater 3. heated solid electrolyte 4
is protected by a protective tube 2 that also takes heat retention into consideration. The outside of the solid electrolyte 4 is exposed to exhaust gas, and the atmosphere is introduced to the heater 5 side. Further, as lead wires, two heater lead wires 22 and two solid electrolyte lead wires 23 are provided.

FIG. 2 is a diagram showing the detection principle of the air-fuel ratio sensor. An A electrode 25 and an E electrode 24 are placed on the atmosphere side and the exhaust side of the solid electrolyte 4.
A diffusion resistor 26 is further provided on the exhaust side. When a voltage is applied using the A electrode 25 as a positive electrode and the E electrode 24 as a negative electrode, oxygen in the exhaust gas passes through the solid electrolyte 4 and flows from the exhaust side to the atmosphere side. When this flow of oxygen is regulated by the diffusion resistor 26, a limiting current proportional to the oxygen concentration in the exhaust gas is obtained. The output characteristics of the air-fuel ratio detector when this current value is converted into a voltage value are shown by the solid line in Figure 3. Since the excess air ratio λ is proportional to the oxygen concentration in the exhaust gas, the excess air ratio λ Proportional output voltage is obtained.

Here, whether the thickness of the diffused resistor 26 or the E electrode 24 is thick,
Or, if the porosity is small, the output power is as shown in Figure 3 (a).
as shown by the broken line.

Further, if the thickness of the diffused resistor 4 or the E electrode 24 is thin or the porosity is large, the output voltage will be high and deviated as shown by the broken line in FIG. 3(b). Such manufacturing variations cannot be strictly avoided. Therefore, this variation must be corrected.

On the other hand, the solid electrolyte 4 is heated and activated by the heater 3;
At this time, if the temperature of the solid electrolyte 4 is higher than the set value, the third
The output voltage becomes high as shown by the broken line in FIG. 3(B), and conversely, when the temperature is low, the output voltage becomes low as shown by the broken line in FIG. 3(B). Therefore, if the resistance value of the heater 3 varies during the manufacturing stage, accurate temperature control cannot be achieved. For this reason, it is also necessary to correct variations in the resistance value of the heater 3.

FIG. 4 shows an embodiment of a circuit for this correction.
, a solid electrolyte compensation resistor 28, a heater circuit 29, a solid electrolyte circuit 30, and a circuit board section 31. In the figure, a constant voltage' or a constant current is supplied to the heater 3 from a circuit 29 in a circuit board M section (including a microcomputer). The heater compensation resistor 27 is provided on the S section side of the intermediate connector section (0 section) when connecting the sensor section (8 section) and the M section.

Therefore, the uncut portion of part 0 is on the left side of the arrow part in FIG. By adjusting the resistance value of the heater compensation resistor 27, the sum of the resistance value of the heater 3 and the resistance value of the heater compensation resistor 27 is made constant for all products. By doing so, variations in the resistance value of the heater 3 can be compensated for on the S section side. Note that the compensation resistor 27
Possible methods for adjusting the resistance value include, for example, using laser trimming or a potentiometer.

On the other hand, the solid electrolyte 4 has terminals 33 and 34 in the circuit 30.
A more constant voltage is supplied, and the current value flowing through the solid electrolyte 4 at this time is detected at the terminals 32, 33 as the voltage value across the solid electrolyte compensation resistor 28. The detected voltage value becomes the output voltage of the detector shown in FIG.

In this case, by changing the resistance value of the compensating resistor 28, its output voltage can be freely changed as shown in FIGS. 3(a) and 3(b). That is, it becomes possible to adjust the gain of the output voltage. Therefore, the part of the solid electrolyte 4 exposed to the exhaust gas is placed in an atmosphere with a known oxygen concentration, and a certain set voltage Vs is applied to the terminals 35° and 36 as shown in FIG. The resistance value of the compensation resistor 28 is adjusted so that the voltage VT is constant for all products. Thereby, manufacturing variations in the solid electrolyte 4 can be compensated for. Note that the known oxygen concentration may be, for example, the oxygen concentration in the atmosphere. Further, the resistance value of the compensating resistor 28 may be adjusted by, for example, laser trimming or a potentiometer, as in the case of the resistor 28.

Figure 6 is an actual overview diagram when the circuit shown in Figure 4 is commercialized, including the sensor section (8 parts) and the four lead wires 22.
．． 23 is taken out and connected to the connector part (part 0). The connector part (0 parts) is the sensor part (8 parts)
It consists of a connector 38 on the side and a connector 39 on the side of the circuit section (M section), and the compensation resistor 27 for the heater and the compensation resistor 28 for the solid electrolyte are installed in the connector 38 on the sensor side.

FIG. 7 is a detailed diagram of the heater circuit 29.

In the figure, 40 is a microcomputer, 41 is a transistor, 42 is a coil, and 43 is a switch. When the transistor 41 is turned on by a signal output from the microcomputer 40, a voltage V is applied to the coil 42.
D acts, the switch 43 is turned on, and the heater 3
A voltage VD is applied to. Conversely, when the microcomputer 40 outputs an OFF signal, the transistor 41 is turned off, the switch 43 is also turned off, and the voltage VD is no longer applied to the heater 3.

quality FIG. 8 is a detailed diagram of the solid-state type circuit 30.

In the same figure, 44 is an operational amplifier, 45 is an operational amplifier,
46 is a transistor, and 47.48 is a resistor. In this circuit 30, the voltage applied to the solid electrolyte 4 is applied to the resistor 47.4 by the operational amplifier 44 and the transistor 46.
It is controlled to have a constant voltage value divided by 8. Furthermore, the value of the current flowing through the compensation resistor 28 is detected and amplified by the operational amplifier 45, resulting in a detection output (■). . It is sent as t. In this circuit 30, the gain is adjusted by the compensation resistor 28, so no adjustment is required on the circuit side.

FIG. 9 is a diagram showing an application example of the connection relationship between the heater connector part and the circuit, in which the current flowing through the heater 3 is detected as a voltage value across the compensation resistor 27, and the current flowing through the heater 3 is detected as a voltage value across the compensating resistor 27. It is controlled by an operational amplifier 49 and a transistor 50 so that it is always constant. According to the configuration, the connector part (part 0) has three circuit side terminals.

FIG. 10 shows that a constant current is excited to the solid electrolyte 4, and
FIG. 3 is a diagram illustrating a method of calibrating a type of sensor that controls the air-fuel ratio by controlling the voltage value that changes between v to 0.5V. In the figure, a variable resistor 52 is provided in the connector part (part 0) in parallel with the solid electrolyte 4, and when the solid electrolyte 4 is placed in an atmosphere with a known oxygen concentration, Flow the current I8 and adjust the resistor 52 so that it varies between 0 and 1V and settles around 0.5V as shown in Figure 11 (same as adjusting the current QA flowing through the solid electrolyte 4). ). This allows correction of sensor variations. Note that 53 in FIG. 10 is a constant current generating circuit, and 54 is a voltage detector.

FIG. 12 is a diagram showing an example of the circuit 54 in FIG. 10, in which changes in the electromotive force of the sensor (O to IV) are detected by the operational amplifier 55, and the ON, O
An FF output signal is sent out.

Figure 13 shows an application example of the air-fuel ratio detection method.
This method allows measurement even in a region where the excess air ratio λ is smaller than 1.0. That is, when λ<1.0, Fig. 13 (a
), by applying the voltage {circle around (2)}B1, oxygen is introduced into the diffusion resistor 26.

Next, the amount of oxygen remaining after the injected oxygen reacts with the carbon monoxide in the exhaust gas inside the diffusion resistor 26 is determined by the voltage Vll
Detection is performed by applying (opposite polarity to VB).

Therefore, when this detected current value is integrated, a characteristic as shown by the solid line (a) in FIG. 14 is obtained.

That is, in this case, as shown in FIG. 13), it is necessary to time-divisionally apply voltages (18) and (vIII) having different polarities to the solid electrolyte 4.

When λ>1.0, oxygen is present in the exhaust gas, so there is no need to send oxygen into the diffusion resistor 26, and it is only necessary to move it to the atmosphere side. When converting the current value with ■8 being applied at this time to a voltage value, the solid line in Figure 14 (
1)).

FIG. 15 shows an embodiment of a circuit for realizing the detection method explained in FIG. 13, in which 56 to 58 are transistors, 59 to 61 are coils, 62 to 64 are switches,
65 is an operational amplifier.

The transistors 56 to 58 are turned on at appropriate times according to the output signal of the microcomputer 40.

The coils 59 to 61 are brought into the OFF'F state, and voltage VD is applied to each of the coils 59 to 61 at appropriate times. As a result, the switches 62 to 64 are turned ON and OFF, and the voltage signals shown in FIG. In addition, the voltage across the compensation resistor 28 is detected and amplified by the operational amplifier 65, resulting in a detection output (■). □Fold and send.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a variable resistor is connected to the sensor body to compensate for manufacturing variations in the resistance values of the solid electrolyte's diffused resistor, electrodes, and heater. Since it is installed inside the connector, there is no need to compensate for variations on the circuit side, and there are benefits such as improved compatibility with the circuit, increased mass production, and easier reduction of cost and maintenance costs. .

[Brief explanation of drawings]

Fig. 1 is a sectional view of the sensor body used in the present invention, Fig. 2 is a sectional view of the solid electrolyte, Fig. 3 is a sensor characteristic diagram, Fig. 4 is a wiring diagram of the external circuit, connector, and sensor section, and Fig. 5 Figure 10 is a diagram showing an application example of a solid electrolyte circuit, Figure 11 is a characteristic diagram when calibrating characteristics, Figure 12 is the circuit shown in Figure 10. 54 detailed diagram, Fig. 13 is a principle diagram showing another example of the air-fuel ratio measurement method, Fig. 14 is a characteristic diagram obtained using the method shown in Fig. 13, and Fig. 15 realizes the measurement method shown in Fig. 13. FIG. 3... Heater, 4... Solid electrolyte, 26... Diffusion resistor, 27.28... Compensating resistor, 29...
Heater circuit, 30...Solid electrolyte circuit, 38.
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Claims (2)

[Claims] 1. In an air-fuel ratio detector that detects the air-fuel ratio of a combustor using exhaust gas, the air-fuel ratio detector includes a first variable resistor for correcting variations in resistance of a diffusion resistor, an electrode, etc. of the air-fuel ratio detector, and an air-fuel ratio detector. An air-fuel ratio detector, characterized in that a second variable resistor for correcting variations in resistance value of a heater added to the heater is provided in an external circuit including a drive circuit of the air-fuel ratio detector. 2. 2. The air-fuel ratio detector according to claim 1, wherein the first and second variable bodies are provided in a connector on the air-fuel ratio detector side that connects the air-fuel ratio detector and an external circuit.