JP2000214131A - Apparatus for controlling air-fuel ratio and method for measuring the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for controlling an air-fuel ratio and a method for measuring an air-fuel ratio whose structure is simple and whose circuit can be simplified. SOLUTION: A signal from a λ. sensor is read in step 100. It is judged on the basis of the read signal in step 110 whether an air-fuel ratio of a gas to be measured is rich or lean. When the air-fuel ratio is judged to be rich, a minute voltage is impressed in a minus direction in step 120. On the other hand, when the air-fuel ratio is judged to be lean, the minute voltage is impressed in a plus direction in step 130. A pump current flowing according to the voltage impressed in each direction is measured in step 140. The air-fuel ratio is roughly obtained from the measured pump current in step 150. A voltage corresponding to the rough air-fuel ratio is impressed to a pump cell in step 170. The pump current is measured in step 180 and, a correct air-fuel ratio is obtained from the pump current in step 190.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control device for an air-fuel ratio sensor having a pump cell and an air-fuel ratio measuring method using the air-fuel ratio sensor.

[0002]

2. Description of the Related Art Conventionally, as an air-fuel ratio sensor for measuring an air-fuel ratio over a wide range, a full-range air-fuel ratio sensor (UEGO sensor) having a structure in which plate-shaped zirconia is superposed in three layers is known.

As shown in FIG. 9, for example, a full-area air-fuel ratio sensor of this type includes porous electrodes P on both sides of a solid electrolyte body P1.
2, an oxygen pump cell (Ip cell) P4 for pumping oxygen (O ₂ ) having P3, and porous electrodes P6, P7 on both sides of the solid electrolyte body P5 to measure the oxygen concentration from the electromotive force. Cell (Vs cell) P8 to be performed and a space (measurement chamber) P provided between the cells P4 and P8.
9, a porous rate-controlling layer P1 communicating the measuring chamber P9 with the outside world
0, and a space (reference chamber) P12 provided between the Vs cell P8 and the shielding layer P11 to store oxygen.

In this full range air-fuel ratio sensor, the V
s cell P8 monitors the atmosphere in the measurement chamber P9, as the electromotive force of the Vs cell P8 is for example 0.45 V, with the first layer of the Ip cell P4, pumping of O ₂ in the measuring chamber P9 (Or pumping). At this time, the pump current flowing through the Ip cell P4 is measured, and the air-fuel ratio of the gas to be measured is measured from the relationship between the pump current and the air-fuel ratio.

[0005]

However, in the above-described full-range air-fuel ratio sensor, three zirconia sheets (Ip cell P4, Vs cell P8, and shielding layer P11) are used in the element portion, so that the structure is used. However, there is a problem that the manufacturing process is increased and the manufacturing cost is increased.

Further, since the control of the Vs cell P8 and the Ip cell P4 and the measurement of the current of the Ip cell P4 must be performed at the same time, the circuit for measuring the air-fuel ratio becomes complicated, and similarly, the number of manufacturing steps is increased. From this point, there is a problem that the manufacturing cost is increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide an air-fuel ratio sensor control device and an air-fuel ratio measuring method which have a simple structure and can be simplified in circuit. Is to do.

[0008]

Means for Solving the Problems (1) In order to achieve the above object, the invention of claim 1 provides a pump cell having a solid electrolyte body and a pair of porous electrodes for pumping oxygen, and An air-fuel ratio sensor comprising: a measurement chamber in contact with one of a pair of porous electrodes; a shielding unit that shields the measurement chamber from the outside world; and a rate-controlling unit that communicates the measurement chamber with the outside world to control gas diffusion. The control device is connected to a λ sensor whose output changes rapidly at the stoichiometric air-fuel ratio point, and determines whether the air-fuel ratio of the gas to be measured is rich or lean based on the output of the λ sensor. Air-fuel ratio determining means,
A voltage control unit that applies a minute voltage to the pair of porous electrodes of the pump cell according to the determination result of the air-fuel ratio determination unit, and a pump current that flows through the pump cell when the voltage is applied by the voltage control unit. Current measuring means for measuring;
From the magnitude of the current measured by the current measuring means,
A control device for an air-fuel ratio sensor, comprising: air-fuel ratio estimating means for estimating a rough value of the air-fuel ratio.

The structure of the air-fuel ratio sensor according to the present invention is as follows.
Instead of the conventional three-layer structure in which three zirconia sheets are laminated, a pump cell (3) and a shielding part (5) are laminated with a measurement chamber (7) interposed therebetween as illustrated in FIG. It has a simple two-layer structure. In this air-fuel ratio sensor, the flow of the gas to be measured between the measurement chamber (7) and the outside is gas diffusion-controlled by the rate-controlling section (9). This is a so-called limiting current type sensor in which a limiting current (without change) appears.

Next, the operation of the air-fuel ratio sensor control device of the present invention for controlling the air-fuel ratio sensor having this structure will be described.
First, in the present invention, since the λ sensor whose output changes rapidly at the stoichiometric air-fuel ratio point is connected to the control device, the output of the λ sensor determines whether the air-fuel ratio of the gas to be measured is rich or lean. Can be determined.

In accordance with the result of the rich / lean judgment by the air-fuel ratio judging means, a minute voltage is applied to the pair of porous electrodes of the pump cell by the voltage controlling means. By means, the pump current flowing through the pump cell is measured. Next, a rough value of the air-fuel ratio is estimated by the air-fuel ratio estimating means from the magnitude of the current measured by the current measuring means.

For example, as shown in FIG. 2, there is a certain relationship between the pump current and the air-fuel ratio. This relationship is
Although not so strict, if this relationship is determined in advance by experiments or the like, a rough air-fuel ratio can be determined from the pump current. Note that the minute voltage is set to, for example, 0.1 to 0.3 so that the pump current is stabilized in a short time after voltage application.
A small voltage of V (for example, 0.2 V) is preferable.

(2) In the invention according to claim 2, when the air-fuel ratio detecting means determines that the air-fuel ratio of the gas to be measured is rich, a voltage is applied to the pair of porous electrodes in opposite directions, On the other hand, when the air-fuel ratio of the gas to be measured is determined to be lean, the control device for the air-fuel ratio sensor according to claim 1, wherein a voltage is applied to the pair of porous electrodes in a positive direction. Make a summary.

The present invention shows a direction in which a minute voltage is applied. Here, for example, as shown in FIG. 3A, the case where the positive electrode of the power supply is connected to the outer porous electrode, the negative electrode of the power supply is connected to the inner porous electrode, and a voltage is applied, It is assumed that a voltage is applied in the positive direction (positive direction). Thereby, oxygen is pumped out of the measurement chamber to the outside world. On the other hand, as shown in FIG. 3 (b), when the positive electrode of the power supply is connected to the inner porous electrode and the negative electrode of the power supply is connected to the outer porous electrode, Assume that a voltage is applied in the negative direction. Thereby, oxygen is pumped into the measurement chamber from the outside.

In the present invention, for example, as shown in FIG.
Voltage in the negative direction (for example, -0.2 in a rich region)
A rough air-fuel ratio in rich can be obtained from the pump current (Ip) when V) is applied. Further, a rough air-fuel ratio in lean can be obtained from a pump current when a voltage (for example, +0.2 V in a lean region) is applied in the positive direction.

The direction of applying the voltage as in the present invention is determined when the voltage is applied in the plus direction in the rich state and when the voltage is applied in the minus direction in the lean state. Because the relationship with the air-fuel ratio is not so clear, it is preferable to obtain a rough air-fuel ratio from the pump current when a voltage is applied in the minus direction in a rich state and when a voltage is applied in a plus direction in a lean state. is there.

(3) According to the invention of claim 3, the relation storage means for storing relation data between the air-fuel ratio of the gas to be measured and the applied voltage at which the limiting current characteristic appears in the pump cell, and the relation storage means. Using relation data, an applied voltage determining means for determining the applied voltage corresponding to the air-fuel ratio estimated by the air-fuel ratio estimating means, and applying the applied voltage determined by the applied voltage determining means to the pump cell. An air-fuel ratio sensor control device according to claim 1 or 2, further comprising: air-fuel ratio detection means for detecting an air-fuel ratio of the gas to be measured from a pump current flowing through a pump cell. .

In the present invention, data on the relationship between the air-fuel ratio of the gas to be measured and the applied voltage at which the limiting current characteristic appears in the pump cell (hereinafter, the applied voltage corresponding to the limiting current is also referred to as the limiting applied voltage) is stored in advance. Using this relationship data, the limit applied voltage corresponding to the estimated air-fuel ratio is determined.

For example, as shown in FIG. 4, a relationship between a certain range of the air-fuel ratio and a limit applied voltage which is an applied voltage (Vp) corresponding to the range is set, and from the relationship, a rough air-fuel ratio is obtained. The corresponding limit applied voltage is determined. Then, the limit application voltage determined in this way is applied to the pump cell, the pump current obtained at this time is measured, and the accurate air-fuel ratio of the gas to be measured is detected from the magnitude of the pump current.

Next, the principle by which an accurate air-fuel ratio can be detected by the above-described procedure will be described. As shown in FIG. 5, the relationship between the air-fuel ratio (A / F or λ) and the limit current (the pump current Ip which is a limit in a certain range) is obtained by an experiment or the like when a voltage is applied to the pump cell. . In this case, even if the applied voltage of the pump cell is slightly changed, the limit current does not change. This is because, as shown in FIG. 6, when the air-fuel ratio changes, the limit current changes (vertical direction in the figure). However, even if the applied voltage (Vp) to the pump cell is changed, the limit current remains within a predetermined range. If, constant current value (limit current)
Is obtained.

Therefore, when a rough air-fuel ratio estimated by the air-fuel ratio estimating means is obtained, a limit applied voltage corresponding to the estimated air-fuel ratio is obtained from FIG. 4 (or FIG. 5). . If this limit applied voltage is applied to the pump cell, a limit current corresponding to the air-fuel ratio can be obtained from the above-described characteristics. Therefore, when the limit applied voltage is actually applied to the pump cell, the pump current (ie, the limit current) Current) and applying the measured limit current to relational data (such as a map) as shown in FIG. 6 to obtain an accurate air-fuel ratio.

(4) The invention according to claim 4 is a pump cell having a solid electrolyte body and a pair of porous electrodes for pumping oxygen, a measuring chamber in contact with one of the pair of porous electrodes, An air-fuel ratio measuring an air-fuel ratio of a gas to be measured by using an air-fuel ratio sensor including a shielding unit that shields the chamber from the outside, and a rate-controlling unit that controls the gas diffusion by communicating the measurement chamber with the outside. In the measurement method, it is determined whether the air-fuel ratio of the gas to be measured is rich or lean based on the output of the λ sensor whose output changes suddenly at the stoichiometric air-fuel ratio point. Air-fuel ratio measurement characterized by applying a minute voltage, measuring the pump current flowing through the pump cell when the voltage is applied, and estimating a rough value of the air-fuel ratio from the magnitude of the measured current. The method is summarized.

In the present invention, a rough value of the air-fuel ratio is estimated using the principle described in the first aspect of the present invention. (5) In the invention according to claim 5, when the air-fuel ratio of the gas to be measured is determined to be rich, a voltage is applied to the pair of porous electrodes in opposite directions, while the air-fuel ratio of the gas to be measured is increased. The gist of the control device for an air-fuel ratio sensor according to claim 5, wherein a voltage is applied to the pair of porous electrodes in a positive direction when it is determined to be lean.

In the present invention, a minute voltage is applied to the pump cell in the same manner as in the second aspect of the present invention. (6) The invention according to claim 6, wherein an applied voltage at which a limiting current characteristic appears in the pump cell is obtained in advance, the applied voltage corresponding to the estimated air-fuel ratio is determined, and the determined applied voltage is used as the pump cell. In addition, at this time, the air-fuel ratio is detected from the pump current flowing through the pump cell, and the air-fuel ratio measuring method according to the above-mentioned claim 6 is summarized.

In the present invention, an accurate air-fuel ratio is detected from the pump current using the principle described in the third aspect of the present invention. Here, as the solid electrolyte of the pump cell, a substance capable of pumping oxygen when a voltage is applied, that is, for example, zirconium, which has oxygen ion conductivity, can be used. In addition, as the porous electrode, a platinum electrode can be used.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment (embodiment) of an air-fuel ratio sensor control apparatus and an air-fuel ratio measuring method using the same according to the present invention will be described below with reference to the drawings. (Example) a) First, the configuration of the air-fuel ratio sensor will be described.

As shown in FIG. 1, the air-fuel ratio sensor 1 includes a pump cell 3 and a shielding section 5 and a measuring chamber 7 provided between the pump cell 3 and the shielding section 5.
And a rate limiting section 9. That is, the air-fuel ratio sensor 1 is a two-layer sensor in which the two plate-shaped members of the pump cell 3 and the shielding part 5 are stacked. If necessary, a heater (not shown) for heating the pump cell 3 may be provided outside the pump cell 3.

The pump cell 3 is provided with rectangular porous electrodes 13 a and 13 b (collectively 13) on both sides of a solid electrolyte layer 11 made of a thin zirconia ceramic sheet. Oxygen pumping is performed by applying a voltage.

Specifically, as shown in FIG. 3A, the positive pole of the power supply is connected to the outer porous electrode 13a, the negative pole of the power supply is connected to the inner porous electrode 13b, Is applied, it is assumed that a voltage is applied in the positive direction (positive direction). Thereby, oxygen is pumped out of the measurement chamber 7 to the outside world. On the other hand, as shown in FIG. 3B, the case where the positive electrode of the power source is connected to the inner porous electrode 13b and the negative electrode of the power source is connected to the outer porous electrode 13a and a voltage is applied, It is assumed that a voltage is applied in the reverse direction (negative direction). Thereby, oxygen is pumped into the measurement chamber 7 from the outside.

As shown in FIG. 1, the shielding portion 5
It consists of a solid electrolyte layer made of thin zirconia ceramics and blocks the passage of gas between the measurement chamber 7 and the outside. The measurement chamber 7 is a space sandwiched between the pump cell 3 and the shielding part 5, and faces the inner porous electrode 13b.

The rate controlling portion 9 is formed by packing a porous filler made of, for example, alumina or the like, and communicates the measurement chamber 7 with the outside world and controls the gas diffusion. b) Next, the configuration of the control device for the air-fuel ratio sensor will be described. As shown in FIG. 7, the control device of the air-fuel ratio sensor includes an electronic control unit (ECU) 15 which is a microcomputer connected to the air-fuel ratio sensor 1.

The ECU 15 is connected to the inner porous electrode 13b via the first wiring 17 and connected to the outer porous electrode 13a via the second wiring 19. First wiring 1
7 is connected to a first amplifier 21, and the second wiring 19 is connected to a second amplifier 23 and a resistor 25. Furthermore, the second
The wiring 19 has a second wiring 19 due to a voltage drop between the resistors 25.
The third wiring 27 and the fourth wiring 29 branch to detect the current flowing through the ECU 1 (therefore, the pump current Ip).
5 is connected.

A display device 31 is connected to the ECU 15 for displaying the measured air-fuel ratio. Particularly, in the present embodiment, the λ sensor 33 whose output changes rapidly at the stoichiometric air-fuel ratio point is connected to the ECU 15. Therefore, based on the signal from the λ sensor 33, it is possible to quickly determine whether the air-fuel ratio of the measured gas is rich or lean.

With the configuration described above, the pump current (Ip) flowing at that time can be detected by making the first wiring 17 side positive or the second wiring 19 side positive. Further, as will be described in detail later, a rough estimation of the air-fuel ratio can be performed from the pump current, so that it is possible to further determine the limit applied voltage and accurately detect the air-fuel ratio.

C) Next, a method of measuring the air-fuel ratio using the control device for the air-fuel ratio sensor described above will be described with reference to the flowchart of FIG. First, in step 100 of FIG. 8, a signal from the λ sensor 33 is read. In the following step 110, it is determined whether the air-fuel ratio (atmosphere) of the measured gas is rich or lean based on the read signal.

If it is determined that the signal is rich, a small voltage (for example, -0.2 V) is applied in the negative direction (reverse direction) in step 120, and step 140 is performed.
Proceed to. Thereby, for example, the pump current (Ip) in the rich region in FIG. 2 flows.

On the other hand, if it is determined that the vehicle is lean, a small voltage (for example, +0.2 V) is applied in the plus direction (positive direction) in step 130, and the process proceeds to step 140. Thereby, for example, a pump current (Ip) flows in the lean region of FIG. Then, in step 140, the pump current (Ip) flowing according to the voltage applied in each direction is measured.

In the following step 150, a rough air-fuel ratio is obtained from each of the measured pump currents. Specifically, when -0.2 V is applied in the rich case, a pump current in the negative direction is obtained. By applying the current value to, for example, the graph of FIG. 2, the air-fuel ratio on the rough rich side is obtained. Can be estimated. In addition, in the case of lean, when +0.2 V is applied, a positive pump current can be obtained. Therefore, by applying the current value to the graph of FIG. 2, a rough estimate of the air-fuel ratio on the lean side can be obtained. Can be.

Next, at step 160, a voltage corresponding to the approximate air-fuel ratio obtained at step 150 is determined. That is, the voltage (limit applied voltage) to be applied to the pump cell 3 is determined using, for example, the relation data (map) shown in FIG. In the following step 170, the limit applied voltage is applied to the pump cell 3.

In the following step 180, the pump current (limit current) flowing through the pump cell 3 when the limit application voltage is applied to the pump cell 3 is measured. Subsequent step 190
Then, the measured pump current is applied to, for example, relational data as shown in FIG. 5 to obtain an accurate air-fuel ratio, and the present process is ended once.

For example, when a limit application voltage of 0.4 V is applied to the pump cell 3, a limit current in the range of about 0 to 1 mA is obtained. By determining the air-fuel ratio (within 1.20) from FIG. 5, an accurate air-fuel ratio can be obtained.

D) As described above, in this embodiment, the air-fuel ratio sensor 1 having a two-layer structure (in which zirconia plates are laminated) is used, so that the structure is simpler than that of a conventional air-fuel ratio sensor having a three-layer structure. The manufacturing cost can be reduced. Further, the conventional air-fuel ratio sensor
It is necessary to control the s cell and the Ip cell at the same time, so that the control circuit is complicated. However, in the present embodiment, such complicated control is unnecessary. Therefore, the structure of the control circuit can be simplified, and the manufacturing cost can be reduced.

In this embodiment, the λ sensor 33 can quickly determine whether the air-fuel ratio is rich or lean. Further, a rough air-fuel ratio can be estimated from the pump current by applying a small voltage in the plus or minus direction to the pump cell 3 based on the determination result.

In addition, an applied voltage is obtained from the estimated air-fuel ratio, and an accurate air-fuel ratio can be obtained from the pump current flowing when the applied voltage is applied. In addition, the present invention
It is needless to say that the present invention is not limited to the above embodiments, but can be implemented in various modes within the scope of the present invention.

[0045]

As described in detail above, according to the present invention, the structure can be simplified as compared with the conventionally used air-fuel ratio sensor, and the manufacturing cost can be reduced. .

Further, the structure can be simplified as compared with the control circuit of the air-fuel ratio sensor which has been used conventionally, and the manufacturing cost can be reduced. In particular,
With the λ sensor, it is possible to quickly determine whether the air-fuel ratio of the gas to be measured is rich or lean.

The λ sensor is attached to all general automobiles. By using the λ sensor, it is possible to judge whether it is rich or lean at low cost without adding a new sensor or the like. It can be carried out.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an air-fuel ratio sensor according to an embodiment.

FIG. 2 is a graph showing a relationship between a pump current and an air-fuel ratio used for roughly estimating an air-fuel ratio.

FIG. 3 is an explanatory diagram illustrating an operation of an air-fuel ratio sensor that changes according to a direction of an applied voltage.

FIG. 4 is an explanatory diagram showing a rough relationship between an air-fuel ratio and an applied voltage.

FIG. 5 is a graph showing a relationship between an applied voltage, an air-fuel ratio, and a pump current.

FIG. 6 is a graph showing a relationship between an applied voltage and a pump current.

FIG. 7 is an explanatory diagram showing a control device of the air-fuel ratio sensor.

FIG. 8 is a flowchart for accurate air-fuel ratio measurement.

FIG. 9 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Air-fuel ratio sensor 3 ... Pump cell 5 ... Shielding part 7 ... Measurement room 9 ... Rate-limiting part 11 ... Solid electrolyte layer 13, 13a, 13b ... Porous electrode 15 ... Electronic control unit (ECU) 33 ... λ sensor

Claims (6)

[Claims] 1. A pump cell having a solid electrolyte body and a pair of porous electrodes for pumping oxygen, a measurement chamber in contact with one of the pair of porous electrodes, and a shield for shielding the measurement chamber from the outside world A control unit for an air-fuel ratio sensor, comprising: a rate-controlling unit that controls the gas diffusion by communicating the measurement chamber with the outside world. And an air-fuel ratio determining unit that determines whether the air-fuel ratio of the gas to be measured is rich or lean based on the output of the λ sensor, and a pair of the pump cells according to the determination result of the air-fuel ratio determining unit. Voltage control means for applying a minute voltage to the porous electrode; current measurement means for measuring a pump current flowing through the pump cell when applying the voltage by the voltage control means; and voltage measured by the current measurement means. From the size,
An air-fuel ratio sensor control device, comprising: air-fuel ratio estimating means for estimating a rough value of the air-fuel ratio. 2. When the air-fuel ratio of the gas to be measured is determined to be rich by the air-fuel ratio detecting means, a voltage is applied to the pair of porous electrodes in opposite directions, while the air-fuel ratio of the gas to be measured is increased. 2. The control device for an air-fuel ratio sensor according to claim 1, wherein when it is determined that the air-fuel ratio is lean, a voltage is applied to the pair of porous electrodes in a positive direction. 3. A relation storage means for storing relation data between an air-fuel ratio of the gas to be measured and an applied voltage at which a limiting current characteristic appears in the pump cell, and using the relation data stored in the relation storage means, An applied voltage determining means for determining the applied voltage corresponding to the air-fuel ratio estimated by the estimating means; and a pump current flowing through the pump cell when the applied voltage determined by the applied voltage determining means is applied to the pump cell. The control device for an air-fuel ratio sensor according to claim 1 or 2, further comprising: an air-fuel ratio detecting unit configured to detect an air-fuel ratio of the gas to be measured. 4. A pump cell having a solid electrolyte body and a pair of porous electrodes for pumping oxygen, a measurement chamber in contact with one of the pair of porous electrodes, and a shield for shielding the measurement chamber from the outside world. And a rate-determining unit that controls the gas diffusion by communicating the measurement chamber with the outside world.A method for measuring an air-fuel ratio of a gas to be measured using an air-fuel ratio sensor comprising: From the output of the λ sensor where the output changes suddenly at
It is determined whether the air-fuel ratio of the gas to be measured is rich or lean, and a small voltage is applied to a pair of porous electrodes of the pump cell according to the result of the determination, and when the voltage is applied, the pump current flowing through the pump cell is determined. A method for measuring an air-fuel ratio, comprising measuring and measuring a rough value of an air-fuel ratio from the measured current. 5. When it is determined that the air-fuel ratio of the gas to be measured is rich, a voltage is applied in the opposite direction to the pair of porous electrodes, while the air-fuel ratio of the gas to be measured is determined to be lean. 5. The control device for an air-fuel ratio sensor according to claim 4, wherein in the case, a voltage is applied to the pair of porous electrodes in a positive direction. 6. An applied voltage at which a limiting current characteristic appears in the pump cell is determined in advance, the applied voltage corresponding to the estimated air-fuel ratio is determined, and the determined applied voltage is applied to the pump cell. 6. The air-fuel ratio measuring method according to claim 5, wherein an air-fuel ratio is detected from a pump current flowing through the pump cell.