JPS6215450A - Detecting device for air/fuel ratio - Google Patents

Abstract

PURPOSE:To detect an air/fuel ratio signal without causing a potential difference at both ends of a gas sinsitive body element by providing a voltage control means and detecting means for air/fuel ratio signal. CONSTITUTION:A constant voltage impressing means M3 impresses the prescribed direct current voltage on the series circuit formed by the gas sensitive body element M1 varying the resistance value according to the oxygen partial pressure under exhausting and the resistance body M2 connected in series therewith. A voltage control means M4 controls the voltage at both ends of the resistance body M2 to the impressed voltage of the constant voltage impressing means M3 so as to cause no voltage difference at both ends of the gas sensitive body element M1. The detecting means M5 air/fuel ratio signal detects the variation in the current passed to the resistance body M2 from the voltage control means M4 as the signal for air/fuel ratio. No potential difference is caused at both ends of the gas sensitive body element M1, nor the element is deteriorated even in case of the air/fuel ratio becoming lean because of the both ends of the gas sensitive body element M1 being controlled in the same potential always.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention detects the air-fuel ratio of various combustion equipment such as internal combustion engines using a gas sensitive element whose resistance value changes depending on the partial pressure of oxygen in the exhaust gas. The present invention relates to an air-fuel ratio detecting device, and particularly to an air-fuel ratio detecting device configured to prevent temporary characteristic ↑1 deterioration of the gas sensitive element.

[Prior Art] Conventionally, for example, in various combustion equipment such as internal combustion engines, in order to improve fuel consumption and transmission, the air-fuel mixture to be combusted in a combustion vessel has been adjusted to a stoichiometric air-fuel ratio based on the oxygen partial pressure in the exhaust gas. There are devices that perform so-called feedback control of the air-fuel ratio. For example, as one of the air-fuel ratio detection devices used in this type of control device and which detects the air-fuel ratio of the air-fuel mixture from the oxygen partial pressure in the exhaust gas,
T! There is one using a gas sensitive element made of an oxide semiconductor such as 02.5n02.

This detects the air-fuel ratio based on the oxygen partial pressure in the exhaust gas by utilizing the property of the gas sensitive element that its resistance value changes depending on the oxygen partial pressure of the surrounding gas. In the apparatus, in order to output the change in the resistance value of the gas sensitive element as a voltage signal, as shown in FIG.
A resistor 32 having a predetermined resistance value is provided in series with the resistor 3.
A direct current voltage V is applied to a series circuit between the resistor 2 and the gas sensing element 31, and the voltage VO generated across the resistor 32 is detected as an air-fuel ratio signal. That is, when the air-fuel ratio is in a rich range and the oxygen partial pressure in the exhaust gas is small, the gas sensing element 3
When the resistance value of 1 is small, the voltage VO generated across the resistor 32 becomes large; conversely, when the air-fuel ratio is in a lean range, the partial pressure of oxygen in the exhaust gas is large, and the resistance value of the gas sensing element 31 is large, Since the voltage VO generated across the resistor 32 becomes smaller, by detecting this voltage VO as an air-fuel ratio signal, it is possible to detect whether the air-fuel ratio is in a lean region or a rich region.

[Problem to be Solved by the Invention 1] However, in this type of air-fuel ratio detection device, the air-fuel ratio is controlled to be near the stoichiometric air-fuel ratio by air-fuel ratio control, and the air-fuel ratio repeatedly changes between the rich range and the lean range. If it is reversed, it is possible to detect a good air-fuel ratio signal corresponding to the air-fuel ratio. It has been found that if the lean range is continued, an air-fuel ratio signal that does not correspond to the air-fuel ratio will be temporarily detected when the air-fuel ratio control IJ is shifted to normal air-fuel ratio control.

Therefore, the present invention aims to solve the problem when the normal air-fuel If: it, I+ control that controls the air-fuel ratio to near the stoichiometric air-fuel ratio is not executed and the air-fuel ratio is in a lean state frequently. By providing an air-fuel ratio detection device that detects a normal air-fuel ratio signal corresponding to the fuel ratio, it is possible to perform air-fuel ratio control. , Jx was configured as shown below.

[Means for Solving the Problems] That is, the configuration of the present invention as a means for solving the above problems is as shown in FIG. 1, in which the resistance value changes depending on the oxygen partial pressure in the exhaust gas. A predetermined DC voltage is applied to the gas sensitive element M1, a resistor M2 connected in series to the gas sensitive element M1, and a series circuit formed by the resistor M2 and the gas sensitive element M1. In order to prevent a potential difference from occurring between the constant voltage applying means M3 and the gas sensitive body cord M1,
voltage control means M4 for controlling the voltage at the terminal of the resistor M2 to the voltage applied by the constant voltage applying means M3; Fuel ratio signal detection means M
The gist of the present invention is an air-fuel ratio control device characterized by comprising the following.

Here, the reason why the present invention is configured as described above is that when a potential difference occurs between both ends of the gas sensitive element M1, impurities inside the element (for example, alkaline components within the element) are transferred to the high potential electrode side. This is because it has been found that this is caused by migration and accumulation toward the lower potential electrode side. In other words, when the air-fuel ratio is in the lean range, the resistance value of the gas sensitive element M1 becomes large as shown in Figure 2, and a large potential difference occurs between both ends of the gas sensitive element M1, causing a low potential electrode side of the element. It was found that impurities accumulate in the air-fuel ratio control, and even if normal air-fuel ratio control is started, a normal air-fuel ratio signal cannot be obtained due to temporary deterioration of the element due to the accumulation of impurities. The above configuration was adopted so that no potential difference would occur between both ends of the circuit.

In addition, as shown in Figure 2, the reason why a normal air-fuel ratio signal could be detected during normal air-fuel ratio control in which the air-fuel ratio was repeatedly reversed between the lean range and the ridge range was because the air-fuel ratio was This is because in the rich range of the fuel ratio, the resistance value of the gas sensitive element becomes small, and impurities within the element are evenly dispersed within the element by thermal diffusion without creating a large potential difference between both ends of the element.

Here, first, as the gas sensitive element M1, an oxide semiconductor whose resistance value changes as shown in FIG. A resistor commonly used in electric circuits may be used as M2.

In addition, the voltage control means M/'I is arranged so that the voltage applied across the resistor M2 is equal to the predetermined voltage applied by the constant voltage application means M3, that is, the voltage control means M/'I is configured to maintain a potential difference between the ends of the gas sensitive element M1. This is to control the elements to prevent them from deteriorating, and can be constructed in a cylinder using an electrical circuit using an operational amplifier or the like.

Furthermore, the air-fuel ratio signal detection means M5 detects changes in the current flowing through the resistor M2 from the voltage control means M4 as an air-fuel ratio signal. If the value is small, the voltage applied from the constant voltage applying means M3 is applied to the resistor M2 as almost 1V, so the current flowing from the current control means M4 to the resistor M2 is small, and conversely, the air-fuel ratio is lean. When the resistance value of the gas sensitive element M1 is large, the voltage h1 applied by the constant voltage applying means M3 is consumed by the gas sensitive element M1, and the current flowing from the current controlling means M4 to the resistor M2 becomes large. By detecting the current, the resistance value of the gas sensitive element M1, which changes in accordance with the air-fuel ratio, is detected, that is, the air-fuel ratio.

[Operation] In the air-fuel ratio detecting device N of the present invention configured as described above, both ends of the gas sensing body cord M1 are always controlled to have the same potential. Therefore, even when the air-fuel ratio becomes lean, no potential difference is generated between the ends of the gas sensing member cable M1, and the cable does not deteriorate.

[Example 1 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows a detection element equipped with a titania element 1 (corresponding to the gas sensitive element M1) installed in the gas system of an internal combustion engine and whose resistance value changes depending on the partial pressure of oxygen in the air. FIG. 2 is an exploded perspective view showing the configuration of part 2;

As shown in the figure, the detection element part 21 is made of alumina or the like and has a thickness of 0.7 mm! Using thick film technology, a heat generating resistor pattern 4 which will serve as a jetter is formed on one side of the flat plate-shaped electrical insulating part vI3, and electrode patterns 5a and 5[) which will serve as electrodes of the titania element are formed. The electrodes 5a and 5b are formed on these pattern surfaces so as to be exposed.
An electrically insulating bamboo part 6 having a thickness of about 0.1 mm and having a cut-out opening 6a is bonded, and an approximately 0.1 mm thick electrically insulating bamboo part 6 having a ditania as a main component and being bonded to the electrode patterns 5a and 5F) is further bonded to the opening 6a. It is made by providing a titania element 1 of about 150μ. Further, A, B, and C shown in the figure are legitimate children used for applying voltage to the detection element section 2 and extracting a detection signal, respectively, and terminals A and C are terminals at both ends of the heating resistor pattern 40. The terminal B is provided at one end of the electrode pattern 5b of the titania element 1. The other electrode pattern 58, on which the titania element 1 is provided, The heater voltage applied to the heating resistor pattern 4 is divided to apply a predetermined voltage to the titania element 1.The heating resistor pattern 4 heats the titania element 1. This is to enable the air-fuel ratio detection to be performed satisfactorily.

Next, FIG. 4 is a circuit diagram showing the entire air-fuel ratio detection device including the detection element section 2. As shown in FIG.

In the figure, resistors R1 and R2 represent the heating resistor pattern 5 of the detection element section 2, and a battery B1 is connected between terminals A and C at both ends of which a heater voltage V1 is applied. Further, the polycomb VR1 connected to the midpoint of the resistors R1 and R2 represents the titania element 1 whose resistance value changes depending on the oxygen partial pressure in the exhaust gas, and the electrode pattern 5a side of the titania element 1 has a resistance R
1 and R2, that is, a voltage V2 divided by the heating resistor pattern 5 is applied. On the other hand, a resistor R3 (corresponding to the resistor 3) having a predetermined resistance value is connected to a terminal B formed at the end of the electrode pattern 5b of the titania element 1, and is grounded.

Next, in addition to the resistor R3, the voltage of this terminal B is connected to terminal B.
A voltage control circuit 1° is connected to the titania element 10 to maintain the voltage at 1-2 and prevent a potential difference from occurring between both ends of the titania element 10.

As shown in the figure, this voltage control circuit 10 is connected to an operational amplifier OP.
1, the inverting input terminal (-) of the operational amplifier 0P10 is connected to the grounded terminal B via the resistor R3, and the output terminal is connected via the resistor R/I with the same resistance value as the resistor R3. is connected 5. On the other hand, the operational amplifier O
The non-inverting input terminal (10) of P1 is connected to the resistors R1 and R2, which divide the voltage v1 from the battery B1 so that the voltage becomes the voltage V2 applied to the electrode pattern 5a side of the titania element 1. Resistance R corresponding to the ratio of values
5 and R6 are connected. An output terminal DF is connected to both ends of the resistor R4 in order to output the magnitude of the current supplied from the voltage control circuit to the resistor R3 as an air-fuel ratio signal vO. In addition, each of the above-mentioned resistances is R1=10Ω, R2-1Ω, R3=R4-50Ω in this example.
, R5=10 has a resistance value of Ω, and R6=1 has a resistance value of Ω.

In the air-fuel ratio detection device of this embodiment configured as described above, first, when the air-fuel ratio changes from a lean region to a rich region, the resistance value of the titania element 1 is 1 [kΩ] as shown in FIG. ] to 1[M(]'', terminal B
The voltage decreases. At this time, in order to control the voltage to be constant (V2) in the voltage control circuit 10, a current is supplied to the resistor R3 via the resistor R/1. Therefore, the resistance [
The voltage VO at both ends becomes large, making it possible to detect the lean range of the air-fuel ratio. On the other hand, when the air-fuel ratio changes from the lean region to the ridge region, the resistance value of the titania element 1 decreases from 1 [Mo2 to 1 [kΩ] as shown in FIG. and R
The voltage V2 divided by 2 is applied almost unchanged to the terminal 3. (In 1r, voltage control circuit 10
Since no current is supplied from the resistor 1, the voltage across the resistor 1 becomes small, and the rich range of the air-fuel ratio can be detected. Due to the operation, the voltage at terminal B is always controlled to V2, and whether the air-fuel ratio is in the lean region or the ridge region, the titania element 1
No potential difference occurs between both ends.

Therefore, the impurities inside the titania element 1 will not be biased toward either electrode and the element will not deteriorate, and the air-fuel ratio can be detected accurately.

[Effects of the Invention] As described in detail above, in the air-fuel ratio detection device of the present invention, the voltage control means M4 and the air-fuel ratio signal detection means M5 can operate without creating a potential difference across the gas sensitive element M1.
Air-fuel ratio signals can be detected. Therefore, impurities within the element are biased towards one of the electrodes, causing the gas sensitive element M
The characteristics of No. 2 do not deteriorate, and air-fuel ratio control can always be performed satisfactorily.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the present invention, FIG. 2 is a diagram showing the inhabitation characteristics of the gas sensitive element, FIGS. 3 and 4 show examples of the present invention, and FIG. 3 is a detection element. FIG. 4 is an electric circuit diagram showing the entire air-fuel ratio detection device of this embodiment, and FIG. 5 is an electric circuit diagram showing a conventional air-fuel ratio detection device. Ml... Gas sensitive element M2... Resistor M3... Constant voltage application means M4... Voltage control means M5... Air-fuel ratio signal detection means 1... Titania element 2... Detection element Part 10... Voltage control circuit

Claims (1)

[Scope of Claims] A gas sensitive element whose resistance value changes depending on the partial pressure of oxygen in exhaust gas, a resistor connected in series to the gas sensitive element, and the resistor and the gas sensitive element. and a constant voltage applying means for applying a predetermined DC voltage to a series circuit formed by the above-mentioned gas sensitive element; An air-fuel ratio control device comprising: voltage control means for controlling the voltage; and air-fuel ratio signal detection means for detecting a change in the current flowing through the resistor from the voltage control means as an air-fuel ratio signal.