JP2000356620A - Gas concentration detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make reducible the response delay time of a gas concentration output when a detected gas is switched from a rich gas to a lean gas. SOLUTION: In this device, the gas concentration sensor 100 has a pump cell 110 and a sensor cell 120, while a porous diffusion layer 101 is provided between the cells 110, 120. A switch circuit 300 is connected to a pump first electrode 111 of the gas concentration sensor 100, and a pump cell application voltage is controlled through the switch circuit 300. When an exhaust gas is a lean gas, an oxygen concentration detection circuit 210 controls the pump cell application voltage. When the exhaust gas is a rich gas, a power supply voltage of a power supply circuit 230 smaller than a set voltage in time of the lean gas is set to the pump cell application voltage, and an oxygen discharge into the porous diffusion layer 101 by the pump cell 110 is suppressed. Thereby, residual oxygen and combustible components in the rich gas react to solve a problem of elongation in a response delay time of a gas concentration output caused by adhesion of the combustible components to the electrode 111.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas concentration sensor for detecting a specific exhaust gas component discharged from, for example, an automobile engine, and a gas for suitably obtaining a gas concentration output from the detection result of the gas concentration sensor. The present invention relates to a concentration detection device.

[0002]

2. Description of the Related Art Engines such as automobiles emit a large amount of exhaust gas, and air pollution caused by the exhaust gas has caused serious problems in modern society, and purification standards for pollutants in exhaust gas are becoming stricter year by year. It has become to. Against this background, a NOx sensor capable of accurately detecting NOx concentration in exhaust gas is provided,
A technology for mounting an Ox sensor on a vehicle engine is desired.

Hitherto, various types of so-called composite gas sensors capable of simultaneously detecting the concentration of NOx in exhaust gas and the concentration of oxygen have been proposed. The configuration of this gas concentration sensor will be described with reference to FIG. As this type of gas concentration sensor, those having a two-cell structure or a three-cell structure are known. Here, a two-cell structure including a pump cell for detecting an oxygen concentration and a sensor cell for detecting a NOx concentration is described. A sensor having a structure will be described.

In FIG. 9, a gas concentration sensor 100 is
Pump cell 110, porous diffusion layer 101, sensor cell 1
20, an air duct 102 and a heater 103, and these members are laminated. The sensor 100 is attached to the wall of the engine exhaust pipe at the right end in the figure, and the upper, lower, and left surfaces thereof are exposed to exhaust gas.

More specifically, the pump cell 110 is provided between the porous diffusion layer 101 and the exhaust gas space. A pump first electrode 111 is provided on the exhaust gas side (upper side in the figure) of the pump cell 110, and is located on the porous diffusion layer 101 side (lower side in the figure).
Is provided with a pump second electrode 112. The sensor cell 120 is provided between the porous diffusion layer 101 and the air duct 102. Porous diffusion layer 1 of sensor cell 120
A sensor first electrode 121 is provided on the 01 side (upper side in the figure), and a sensor second electrode 122 is provided on the atmosphere duct 102 side (lower side in the figure). Exhaust gas is introduced into the porous diffusion layer 101 from the left side of the figure and flows to the right side of the figure.

The pump cell 110 and the sensor cell 120 have a solid electrolyte formed by lamination, and these solid electrolytes are formed by converting CrO 2, HfO 2, ThO 2, Bi 2 O 3, etc.
It is composed of an oxygen ion conductive oxide fired body in which aO, MgO, Y2 O3, Yb2 O3, etc. are dissolved as a stabilizer. Further, the porous diffusion layer 101 is made of a heat-resistant inorganic substance such as alumina, magnesia, quartzite, spinel, and mullite.

The first pump on the exhaust gas side of the pump cell 110
The electrode 111 and the sensor first and second electrodes 121 and 122 of the sensor cell 120 are made of a noble metal having high catalytic activity such as platinum Pt. On the other hand, the pump second electrode 112 on the porous diffusion layer 101 side of the pump cell 110 is made of a noble metal such as Au-Pt which is inert to the NOx gas (it is difficult to decompose the NOx gas).

The heater 103 is embedded in the insulating layer 104,
An air duct 102 is formed between the insulating layer 104 and the sensor cell 120. Atmosphere is introduced into the air duct 102 constituting the reference gas chamber from the outside, and the air is used as a reference gas serving as a reference for the oxygen concentration. Insulation layer 1
04 is made of alumina or the like, and the heater 103 is made of cermet of platinum and alumina.

The operation of the gas concentration sensor 100 having the above configuration will be described with reference to FIG. As shown in FIG. 10A, an exhaust gas component is introduced into the porous diffusion layer 101 from the left side of the figure, and when the exhaust gas passes near the pump cell, a decomposition reaction is performed by applying a voltage to the pump cell 110. Occur. The exhaust gas contains oxygen (O2), nitrogen oxide (NOx), carbon dioxide (CO2), and water (H2
O) and other gas components.

As described above, the pump second of the pump cell 110
The electrode 112 is formed of a NOx inert electrode (an electrode that hardly decomposes NOx gas). Therefore, as shown in FIG. 10B, only oxygen (O2) in the exhaust gas is decomposed by the pump cell 110 and discharged from the pump first electrode 111 into the exhaust gas. At this time, the current flowing through the pump cell 110 is detected as the concentration of oxygen contained in the exhaust gas.

Further, oxygen (O2) in the exhaust gas is not completely decomposed in the pump cell 110, and a part of the oxygen (O2) flows as it is to the vicinity of the sensor cell. Then, as shown in FIG. 10 (c), by applying a voltage to the sensor cell 120, residual oxygen (O2) and NOx are decomposed. That is, the residual oxygen (O2) and NOx are decomposed at the sensor first electrode 121 of the sensor cell 120, respectively, and are sent from the sensor second electrode 122 through the sensor cell 120 to the atmosphere duct 1
02 is released into the atmosphere. At this time, the sensor cell 12
The current flowing to zero is detected as the concentration of NOx contained in the exhaust gas. The decomposition current due to residual oxygen (O2) becomes an offset current.

The output characteristics of the pump cell will be described with reference to the VI diagram of FIG. As shown in FIG. 11, the pump cell 110 has a limiting current characteristic with respect to the oxygen concentration.
In the figure, the limit current detection area is composed of a linear portion parallel to the V axis, and the area shifts toward the positive voltage side as the oxygen concentration increases. The applied voltage line LX1 is connected to the pump cell 11
It is given by a linear line having a gradient equivalent to the angle of a DC resistance component of 0 (a gradient portion that increases with an increase in applied voltage). By applying a voltage based on LX1, a desired pump cell is always obtained regardless of the oxygen concentration in exhaust gas. The current (limit current) can be detected. Incidentally, since the pump second electrode 112 is a NOx inactive electrode, the NOx gas is hardly decomposed in the pump cell 110. However, when the voltage exceeds a certain voltage as shown in FIG. And a pump cell current corresponding to the NOx concentration flows (a broken line portion in the figure). Therefore, the applied voltage line LX1 is designed so as not to decompose NOx gas.

Next, the output characteristics of the sensor cell will be described with reference to FIG. As shown in the VI diagram of FIG. 12, the sensor cell 120 has a limiting current characteristic with respect to the NOx concentration. In the figure, a porous diffusion layer 101 is shown in the portion A1.
A current (offset current) corresponding to the offset flows due to the residual oxygen flowing into the sensor cell 120 through the sensor cell 120, and a decomposition current of NOx flows in the portion A2 (1000 ppm in FIG.
Is shown). Further, in a portion where the current larger than "A1 + A2", that is, the current at the right end of the figure increases (when the NOx concentration is 1000 rpm, A3 portion), a decomposition current of H2 O flows. At this time, the limit current detection region that defines the NOx decomposition current includes a straight line portion parallel to the V axis, and the limit current corresponding to the NOx concentration in the exhaust gas is “A1 + A2”.
Is detected at the current value of

[0014]

When a rich gas is introduced into the porous diffusion layer 101, a large amount of combustible components (H2, HC, etc.) are contained in the rich gas.
A combustible component is adsorbed on the sensor first electrode 121. Then, when the exhaust gas changes from rich to lean, the combustible component adsorbed on the sensor first electrode 121 inhibits the decomposition of NOx gas, and the NOx concentration output cannot be obtained correctly for about several tens of seconds. appear. In general, when the exhaust gas is not only a lean gas but also a rich gas, the applied voltage of the pump cell 110 is controlled so that oxygen in the porous diffusion layer 101 is discharged via the pump cell 110. As a result, the combustible components are adsorbed to the electrodes, and the response of the gas concentration output deteriorates when switching from rich gas to lean gas.

The gas concentration detecting device of the present invention has been made in view of the above problem, and aims to reduce the response delay time of the gas concentration output when the gas to be detected such as exhaust gas is switched from rich gas to lean gas. For that purpose.

[0016]

The gas concentration detecting device of the present invention is premised on having a gas introducing portion for introducing a gas to be detected and a pair of electrodes provided so as to sandwich a solid electrolyte. A first cell for flowing a current according to the oxygen concentration while discharging excess oxygen in the gas to be detected in the gas introduction unit with application of a voltage to the gas introduction unit, and a pair of electrodes similarly provided so as to sandwich the solid electrolyte, A gas concentration sensor including a second cell for flowing a current corresponding to the concentration of a specific component from the gas component after excess oxygen is discharged in accordance with the application of a voltage to the electrode.

According to a first aspect of the present invention, there is provided a detecting means for detecting that a gas to be detected is a rich gas, and a detecting means for detecting a gas to be detected as a rich gas. And control means for controlling the applied voltage of the first cell so as to suppress oxygen discharge.

According to the first aspect of the present invention, since the oxygen discharge by the first cell is suppressed at the time of the rich gas, the oxygen remaining in the gas introducing portion and the H2 contained in the rich gas are suppressed.
, HC and other combustible components are promoted. Therefore, when returning from rich gas to lean gas, the second
When the concentration of the specific component (for example, NOx concentration) is detected in the cell, the disadvantage that the gas concentration output is delayed is solved. That is, the problem of the related art in which the combustible component is adsorbed on the electrode of the second cell and the response delay time of the gas concentration output is prolonged due to the adsorbed combustible component is solved. As a result, when the gas to be detected is switched from lean to rich, the response delay time of the gas concentration output is reduced, and the detection accuracy of the gas concentration is improved.

Incidentally, the "detected gas" referred to in this specification refers to all gases containing at least oxygen and flammable components in addition to the exhaust gas of the vehicle engine, and "lean gas" refers to oxygen in the gas. "Rich gas" refers to a state in which the combustible components in the gas are excessive.

Here, in order to suppress the oxygen discharge from the gas introduction part by the first cell, the following configuration can be considered. In other words, according to the second aspect of the invention, when the gas to be detected is detected to be rich gas, the control means sets the voltage (the negative voltage value) smaller than the applied voltage of the first cell set at the time of lean gas. ) Is applied to the first cell. Thus, when the gas to be detected is a rich gas, oxygen discharge from the gas introduction section is reliably suppressed, and adsorption of the combustible component to the electrode can be prevented.

According to a third aspect of the present invention, in the second aspect of the invention, the control means controls the voltage applied to the first cell in accordance with the richness of the gas to be detected, and the richness is large. The lower the applied voltage of the first cell, the lower the voltage. That is, if the degree of richness of the detected gas is large, the amount of combustible components contained in the gas increases, and it is necessary to secure residual oxygen that can sufficiently react with the combustible components. In this case, if the voltage applied to the first cell is reduced as necessary as described above, it is possible to always prevent adsorption of the combustible component to the electrode regardless of the richness of the gas to be detected.

According to a fourth aspect of the present invention, in the second or third aspect of the invention, the control means includes a power supply for applying a voltage to the first cell when the gas to be detected is a lean gas. The power supply of the first cell is switched to the another power supply when the gas to be detected is detected to be a rich gas.

For example, consider the case where the applied voltage is variably set according to the gas concentration at the time of lean gas, while the fixed voltage is set at the time of rich gas. In this case, by using different power supplies for the lean gas and the rich gas as described above, the applied voltage can be suitably controlled regardless of the lean gas / rich gas, and the gas concentration can be correctly detected.

According to the fifth aspect of the present invention, since the application of the voltage to the first cell is stopped at the time of the rich gas, the oxygen discharge in the first cell is suppressed even in such a case,
The problem that the response delay time of the gas concentration output is prolonged due to the attachment of the combustible component to the electrode is solved. In this case, the invention can be implemented with a relatively simple configuration, such as simply grounding or opening the electrode of the first cell.

In the invention according to claim 6, the detecting means is provided for any one of the first and second cells provided between the reference gas chamber and the gas introduction section, the cell being generated when oxygen in the gas introduction section becomes insufficient. It is detected that the gas to be detected is a rich gas according to the electromotive force. When it is detected that the gas to be detected is a rich gas, the control means performs the first operation in a voltage setting range in which the oxygen deficiency state is not released.
Set the voltage applied to the cell. As an example, the applied voltage of the first cell is set in a voltage setting range on the positive side of 0V.

When rich gas detection is performed in accordance with the electromotive force of the first or second cell as described above, if the applied voltage of the first cell is set to be excessively low (for example, set to a negative voltage) as compared with the case of lean gas, gas introduction is performed. There is a possibility that the oxygen deficiency state in the section is inadvertently released, and at that time, it is mistaken that it has returned to the lean gas. In this case, the control of the applied voltage of the first cell is temporarily returned to the control at the time of the normal lean gas, but immediately thereafter, the control is returned to the control at the time of the rich gas again. Thus, when the rich gas / lean gas is alternately detected, the applied voltage is controlled. This causes voltage hunting.

According to the sixth aspect of the present invention, the voltage applied to the first cell is set so that the oxygen deficiency in the gas inlet is not released during the rich gas period. Is suppressed.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings. The gas concentration detection device according to the present embodiment is applied to an automobile gasoline engine, and in the air-fuel ratio control system of the engine, the fuel injection amount to the engine is determined based on the detection result by the gas concentration detection device. Feedback control is performed at a desired air-fuel ratio (A / F). Particularly, in this embodiment, the oxygen (O2) concentration in the exhaust gas and the N
A so-called composite gas sensor capable of simultaneously detecting the Ox concentration is used, and gas concentration information is acquired from the sensor.

That is, in the apparatus of this embodiment, the air-fuel ratio is feedback-controlled based on the detected oxygen concentration, while the NOx catalyst (eg, NOx storage reduction type catalyst) attached to the engine exhaust pipe is controlled based on the detected NOx concentration. Is performed. Briefly describing the control of the NOx catalyst, the amount of NOx discharged without being purified by the NOx catalyst is determined from the detection result of the gas concentration sensor, and when the unpurified amount of NOx increases, the NOx purification capability is restored. Is executed. In the regeneration process, a rich gas may be temporarily supplied to the NOx catalyst to remove ions adsorbed on the catalyst.

FIG. 1 is an overall configuration diagram of a gas concentration detecting device. The detecting device is mainly composed of a gas concentration sensor 100, a control circuit 200, and a switch circuit 300. As the gas concentration sensor 100, the above-described sensor having the two-cell structure shown in FIG. 9 is used, and since the structure, operation principle, and output characteristics have been described above, the description thereof is omitted here. The control circuit 200 is configured as follows.

In the configuration shown in FIG.
The switch circuit 300 is connected to the 0 pump first electrode 111, and the pump cell applied voltage is controlled via the switch circuit 300.

That is, the switch circuit 300 is shown in FIG.
It is switched to either B or C. Switch circuit 300
Is at the position A as shown in the figure, the pump first electrode 111
Is connected to an oxygen concentration detection circuit 210, and the applied voltage to the pump first electrode 111 is controlled by the oxygen concentration detection circuit 210. Further, the switch circuit 300 is connected to B or C in FIG.
When switched to the position, the pump first electrode 111 is connected to the power supply circuit 230. More specifically, when the switch circuit 300 is switched to the position B, the applied voltage of the pump first electrode 111 becomes the predetermined voltage Vc of the power supply 231,
When the switch circuit 300 is switched to the position C, the voltage applied to the pump first electrode 111 becomes “0 V”. In addition,
The pump second electrode 112 is grounded together with the sensor first electrode 121.

According to the power supply circuit 230, a voltage smaller than the voltage value set at the time of the lean gas is applied to the pump cell 110.
Is applied. Specifically, in the VI diagram shown in FIG. 11, when the voltage V0 of the V-axis intercept of the applied voltage line LX1 is about 0.2 V, the voltage value in the power supply circuit 230 is set to less than 0.2 V. Is done. In this embodiment, Vc is set to 0.1 V, and the voltage applied by the power supply circuit 230 is set to 0.2 V or 0 V.

In the oxygen concentration detection circuit 210, the pump voltage command circuit 211 includes a CPU and an A / A as shown in FIG.
D, D / A converter (A / D1, A / D2, D / A
It is composed of a one-chip microcomputer having 1). The command circuit 211 receives the voltages at the terminals Va and Vb in FIG. 1 and controls the command voltage Va to the pump cell 110 based on the voltage values.

The command voltage Va from the pump voltage command circuit 211 is input to the non-inverting input terminal of the amplifier circuit 212. The output terminal of the amplifier circuit 212 is connected to the pump cell current Ip
The other end of the current detection resistor 213 is connected to the contact A of the switch circuit 300 and the inverting input terminal of the amplifier circuit 212. As a result, the voltage at the contact A of the switch circuit 300 is controlled to be always the same as the command voltage Va of the pump voltage command circuit 211.

On the other hand, the second sensor of the gas concentration sensor 100
The electrode 122 is connected to a NOx concentration detection circuit 220 for detecting the NOx concentration. The NOx concentration detection circuit 220 has one end connected to the sensor second electrode 122,
A current detection resistor 221 having the other end connected to the power supply 222;
A current detection circuit 223 for detecting a sensor cell current Is from both terminal voltages of the current detection resistor 221, and a detection result of the current detection circuit 223 is output to a comparison circuit 240.
The detection result of the current detection circuit 223 is output to another control device (not shown) as a NOx concentration output. In addition,
When the exhaust gas is lean gas, the sensor cell current Is is detected as a positive current value, and when the exhaust gas is rich gas, the sensor cell current Is is detected as a negative current value.

The comparison circuit 240 performs lean / rich determination of exhaust gas in accordance with the sensor cell current Is detected by the current detection circuit 223, and based on the determination, determines whether the switching circuit 300
And outputs a switching command signal. More specifically,
When Is> mA0, that is, when it is determined that the exhaust gas is lean gas, the comparison circuit 240
For 0, a signal to the effect that connection A is made is output. Thus, the voltage applied to the pump cell 110 is controlled by the oxygen concentration detection circuit 210. When Is ≦ 0 mA, that is, when it is determined that the exhaust gas is a rich gas, the comparison circuit 240 outputs a signal to the switch circuit 300 to the effect that connection B or C in the drawing is made. Whether to use the B connection or the C connection is selected according to the degree of richness of the exhaust gas, and when the degree of richness is relatively small, the B connection is used.
When the degree of richness is relatively large, C connection is used. As a result, the voltage applied to the pump cell 110 is controlled by the power supply circuit 230.

In this embodiment, the current detection circuit 22
3 and the comparison circuit 240 correspond to “detection means” of the present invention, and the power supply circuit 230 and the switch circuit 300 correspond to “control means”.

FIG. 3 is a circuit diagram showing C in the pump voltage command circuit 211.
5 is a flowchart illustrating an applied voltage control procedure performed by a PU, which is performed as an applied voltage control subroutine in the middle of a main routine (not shown).

In FIG. 3, in steps 101 and 102, both terminal voltages Va and Vb of the current detection resistor 213 in FIG.
Are read by A / D1 and A / D2 in FIG. 2, respectively, and in the subsequent step 103, the pump cell current Ip is calculated as Ip = (Vb−Va) / R1. Where R1 is
This is the resistance value of the current detection resistor 213.

Thereafter, in step 104, a target applied voltage to the pump cell 110 corresponding to the calculated pump cell current Ip is obtained (map calculation) using the applied voltage line LX1 shown in FIG. Further, in step 105, the obtained target applied voltage is set to a command voltage Va as D /
The signal is output via A1, and then this routine is temporarily terminated.

Next, the operation of the present gas concentration detecting apparatus will be described with reference to a time chart of FIG. 4 for a period from the time when the exhaust gas changes from lean gas to rich gas and then returns to lean gas. In FIG. 4, (a) shows the air-fuel ratio of the exhaust gas, (b) shows the pump cell applied voltage,
(C) shows the sensor cell current Is, and (d) shows the state of the switching operation of the switch circuit 300.

Since the exhaust gas is lean gas before time t1 in the figure, the switching position of the switch circuit 300 is the position A in FIG. 1, and the oxygen concentration detection circuit 210 detects the pump cell current Ip (exhaust gas The applied voltage to the pump cell 110 is controlled according to the oxygen concentration of the pump cell 110. At this time, the application voltage is set on the application voltage line LX1 in FIG. 11 as described in FIG. By controlling the applied voltage of the pump cell 110, the oxygen concentration in the porous diffusion layer 101 is maintained at a relatively low concentration.

Also, at the time of the lean gas, since the excess oxygen in the porous diffusion layer 101 flows out to the atmosphere duct 102 through the sensor cell 120, the sensor cell current Is flows from the sensor second electrode 122 to the sensor first electrode 121. It flows in the direction (atmosphere duct 102 side → porous diffusion layer 101 side), which is detected by current detection circuit 223. FIG. 4 shows Is at this time as a positive current. The comparison circuit 240 determines that the exhaust gas is lean gas based on the sensor cell current Is, and keeps the switching position of the switch circuit 300 at the position A in FIG.

When the exhaust gas shifts to a rich gas at time t1, oxygen in the porous diffusion layer 101 gradually becomes deficient, so that a large electromotive force (oxygen concentration cell) is applied to the sensor cell 120.
Occurs, and the sensor cell current Is flows in the direction from the sensor first electrode 121 to the sensor second electrode 122 (the direction from the porous diffusion layer 101 side to the atmosphere duct 102 side), which is opposite to the case of the lean gas. It is detected by the detection circuit 223.

Immediately after time t1, since the sensor cell current Is is in the range of 0 to Ith (Ith <0 mA), the comparison circuit 240 determines that and the switch circuit 300 is switched. That is, although the exhaust gas becomes rich gas, the degree of richness is determined to be relatively small, and the switching circuit 3
The switching position of 00 becomes the position B in FIG.
As a result, the predetermined voltage Vc is applied to the pump cell 110.
At this time, since a voltage lower than the applied voltage up to that time is applied, the porous diffusion layer 1
Oxygen in the diffusion layer 101 is suppressed, and oxygen remaining in the diffusion layer 101 and combustible components (H2, HC, etc.) in the rich gas are reduced.
The reaction with is promoted. That is, the residual oxygen reacts with the combustible components (H2, HC, etc.) to generate H2 O and CO2 which are not adsorbed on the sensor first electrode 121.

Thereafter, when the degree of richness of the exhaust gas increases and the sensor cell current Is falls below a predetermined value Ith, the switching position of the switch circuit 300 becomes the position C in FIG. 1, and the voltage applied to the pump cell becomes 0V. Thereby, oxygen discharge from the porous diffusion layer 101 by the pump cell 110 is interrupted. Accordingly, the reaction between oxygen remaining in the diffusion layer 101 and combustible components (H2, HC, etc.) in the rich gas is promoted, and the sensor first electrode 1 is replaced with the combustible component.
H2 O and CO2 which are not adsorbed by the H. 21 are generated.

If the degree of richness of the exhaust gas is large, the amount of flammable components contained in the gas increases, but the voltage applied to the pump cell is reduced accordingly, so that residual oxygen enough to react sufficiently with the flammable components is secured. You. Therefore, irrespective of the degree of the richness of the exhaust gas, the adsorption of the combustible component to the electrode is always prevented.

Incidentally, in the apparatus of this embodiment, the detection of the gas concentration is temporarily interrupted when the gas is rich. Therefore, even if the applied voltage of the pump cell is controlled to a value different from the normal command value as described above at the time of rich gas and the residual oxygen amount in the porous diffusion layer 101 changes, the NOx concentration output at that time is not used. , NOx concentration is not erroneously detected.

Thereafter, when Is ≧ Ith at time t3, the switching position of the switch circuit 300 is returned to the position B,
Further, when Is ≧ 0 mA at time t4, the switch circuit 3
The switching position of 00 is returned to the A position. When the exhaust gas returns from rich gas to lean gas at time t4, the sensor first
Since no flammable components are adsorbed on the electrode 121, NOx
The decomposition time is not hindered, and the recovery time required until the normal NOx concentration output is started is reduced. That is, the response delay time when returning to lean gas is shortened, and the NOx concentration can be correctly detected immediately after returning to lean gas. After time t4, the pump cell applied voltage is controlled in accordance with the current pump cell current Ip (oxygen concentration in exhaust gas) as usual.

Here, it has been found by the present inventors that the pump cell applied voltage at the time of rich gas and the response delay time at the time of return of the lean gas have the relationship shown in FIG. 5, and according to FIG. It can be seen that the response delay time becomes shorter as is smaller. Therefore, if the voltage applied to the pump cell is simply reduced, the response delay time can be reduced. However, when the lean / rich determination of the exhaust gas is performed by the electromotive force of the sensor cell 120 as described above, if the pump cell applied voltage is set to a negative voltage at the time of rich gas, the porous diffusion layer 101 is inserted into the porous diffusion layer 101 via the pump cell 110. Oxygen is supplied, the amount of residual oxygen in the porous diffusion layer 101 is inadvertently increased, and the operation of temporarily performing lean gas determination and then performing rich gas determination again is repeated. That is, even if the rich gas is continued, the rich gas determination and the lean gas determination are alternately repeated, which causes a disadvantage that the pump cell applied voltage hunts.

On the other hand, if the lower limit value of the applied voltage of the pump cell at the time of the rich gas is set on the negative side and the applied voltage is specified at 0 V or more, the rich gas judgment determined by the sensor cell electromotive force is inadvertently changed. Never
Hunting of the pump cell applied voltage can be prevented. In short, in the apparatus of the present embodiment, by setting the pump cell applied voltage (voltage of the power supply circuit 230) at the time of rich gas to 0 or 0.2 V, the response delay time at the time of lean gas return is shortened, and the pump cell applied voltage at the time of rich gas is reduced. Prevention of hunting.

According to the embodiment described above, the following effects can be obtained. (A) Since the applied voltage of the pump cell at the time of rich gas is made lower than the set voltage at the time of lean gas to suppress the oxygen discharge by the pump cell 110, the response delay time of the gas concentration output at the time of switching from lean gas to rich gas is shortened. Gas concentration detection accuracy is improved.

(B) Since the voltage applied to the pump cell is set to 0 or 0.2 V in accordance with the degree of richness of the exhaust gas, it is possible to always prevent the flammable components from being adsorbed to the electrode regardless of the degree of richness of the exhaust gas.

(C) A power supply circuit 230 is provided separately from the oxygen concentration detection circuit 210 for variably controlling the pump cell applied voltage. Since the power supply circuit 230 controls the pump cell applied voltage at the time of rich gas, either the lean gas or the rich gas is used. Even if there is, the applied voltage can be suitably controlled, and the gas concentration can be correctly detected.

(D) At the time of rich gas, the porous diffusion layer 10
Since the pump cell applied voltage is set in a voltage range where the oxygen deficiency state in 1 is not inadvertently released, hunting of the applied voltage is suppressed.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. The gas concentration sensor 150 of FIG.
The configuration of the gas concentration sensor 150 and the control circuit 201 shown in FIG.
The following description focuses on the differences from this embodiment.

In the gas concentration sensor 150 shown in FIG. 6, the pump cell 160 as the first cell is located upstream and the sensor cell 170 as the second cell is located downstream in comparison with the gas concentration sensor 100 shown in FIG. The positions are the same, but the installation locations of the pump cell 160 and the sensor cell 170 are upside down.

That is, a pump cell 160 for detecting the oxygen concentration is provided between the porous diffusion layer 101 and the air duct 102, and a sensor cell 170 for detecting the NOx concentration is provided between the porous diffusion layer 101 and the exhaust gas space. It is provided between. Of the pump first and second electrodes 161 and 162 and the sensor first and second electrodes 171 and 172 installed in each of the cells 160 and 170, only the pump first electrode 161 on the porous diffusion layer 101 side is Au-. The electrode is formed of a noble metal inert to NOx gas such as Pt (an electrode that hardly decomposes the NOx gas), and the other electrodes are formed of a noble metal having high catalytic activity such as platinum. Gas concentration sensor 150 (cell 1
The detection principle of the gas concentration according to (60, 170) is the same as that of the sensor 100 described above, and the description thereof will be omitted.

FIG. 7 is a VI diagram showing the output characteristics of the pump cell of the gas concentration sensor 150. According to FIG.
It can be seen that the pump cell current (limit current) can be measured not only when the exhaust gas is lean gas but also when it is rich gas. That is, the gas concentration sensor 150 differs from the gas concentration sensor 100 of FIG.
60 is provided between the porous diffusion layer 101 and the air duct 102, so that when the gas is rich gas (the porous diffusion layer 101
It can be detected that the exhaust gas is a rich gas in accordance with the electromotive force of the pump cell 160 generated when oxygen is insufficient in the inside.

In FIG. 7, an applied voltage line L similar to that of FIG.
X1 is prepared, and in the lean gas region (the region of the pump cell current> 0 mA), the LX1 is used to variably set the pump cell applied voltage. In a rich gas region (a region where the pump cell current is <0 mA), the LX
The pump cell applied voltage is variably set using another applied voltage line LX2 that is more negative than 1.

In the apparatus shown in FIG. 6, an oxygen concentration detecting circuit 250 is connected to the pump second electrode 162 of the gas concentration sensor 150. Pump voltage command circuit 251
Is composed of, for example, a one-chip microcomputer including a CPU and A / D and D / A converters, and variably controls a pump cell applied voltage according to a pump cell current Ip at each time. The command voltage Va from the pump voltage command circuit 251 is input to the non-inverting input terminal of the amplifier circuit 252. The output terminal of the amplifier circuit 252 is connected to one end of a current detection resistor 253 for detecting the pump cell current Ip, and the other end of the current detection resistor 253 is connected to the pump second electrode 16.
2 and the inverting input terminal of the amplifier circuit 252. Thus, the voltage of the pump second electrode 162 is controlled to be always the same as the command voltage Va.

On the other hand, the sensor first electrode 171 of the sensor cell 170 is connected to a power supply 261 via a current detection resistor 262 for detecting the sensor cell current Is. Here, the sensor cell current Is is detected from both terminal voltages Vd and Ve of the current detection resistor 262. The first pump electrode 161 and the second sensor electrode 172 are both grounded.

Next, the CP in the pump voltage command circuit 251
The applied voltage control performed by U will be described with reference to the flowchart of FIG. In the present embodiment, the routine of FIG. 8 is executed instead of the routine of FIG.

In FIG. 8, in step 201, both terminal voltages Va and Vb of the current detection resistor 253 are read to calculate a pump cell current Ip (Ip = (Vb-V
a) / R1). In the following step 202, lean / rich determination of exhaust gas is performed based on the calculated pump cell current Ip (direction of Ip).

When it is determined that the exhaust gas is lean gas, the routine proceeds to step 203, where the applied voltage line LX1 shown in FIG.
Is used to obtain a target applied voltage to the pump cell 160 corresponding to the calculated pump cell current Ip (map calculation). Further, in step 205, the obtained target applied voltage is output as the command voltage Va, and then the present routine is temporarily terminated.

When it is determined that the exhaust gas is a rich gas, the routine proceeds to step 204, where the applied voltage line L in FIG.
Using X2, a target applied voltage to the pump cell 160 corresponding to the calculated pump cell current Ip is obtained (map calculation). Further, in step 205, the obtained target applied voltage is output as the command voltage Va, and then the present routine is temporarily terminated. In the present embodiment, step 202 in FIG. 8 corresponds to “detection means” of the present invention, and step 204 corresponds to “control means”.

As described above, according to the second embodiment, the first
Similarly to the embodiment, the pump cell applied voltage at the time of the rich gas is made smaller than the set voltage at the time of the lean gas to suppress the oxygen discharge by the pump cell 110, so that the response delay time of the gas concentration output at the time of switching from the lean gas to the rich gas is reduced. Therefore, the accuracy of detecting the gas concentration is improved. At the same time, hunting of the pump cell applied voltage is suppressed.

In particular, since the applied voltage of the pump cell can be set in accordance with the degree of richness at each time by using the applied voltage line LX2 in FIG. 7, appropriate applied voltage control can always be performed, and the flammable component can be applied to the electrode. Adsorption can be reliably prevented.

The present invention can be embodied in the following forms other than the above. In the first embodiment, when the exhaust gas is a rich gas, the pump cell applied voltage is increased in two steps (0 or 0.1) so as to suppress the oxygen emission from the porous diffusion layer 101.
V), but this configuration is changed as follows.
For example, one voltage value is set as the pump cell applied voltage at the time of rich gas. Alternatively, the same applied voltage of 3
Different voltage values are set in steps or more. In any of these cases, the pump cell applied voltage is set lower than the voltage value at the time of lean gas (in FIG. 11, the V-axis intercept voltage V0 of LX1).
Smaller than 0 V) and a voltage value of 0 V or more so as to achieve both the reduction of the response delay time of the gas concentration output at the time of lean return and the prevention of hunting of the pump cell applied voltage. Similarly, the device of the second embodiment may control the pump cell applied voltage in multiple stages as described above.

In each of the above embodiments, the configuration is such that the application of voltage to the pump cell is stopped at the time of rich gas. Also in such a case, the problem that the oxygen discharge in the pump cell is suppressed and the response delay time of the gas concentration output is prolonged due to the attachment of the combustible component to the electrode is solved. In this case, the invention can be implemented with a relatively simple configuration, such as simply grounding or opening the electrode of the pump cell.

In each of the above embodiments, the porous diffusion layer 10
It is detected that the exhaust gas is a rich gas according to the electromotive force generated in the porous diffusion layer 101 in a cell provided between the gas introduction part 1 and the air duct 102 (reference gas chamber) when oxygen is deficient in the cell. However, this configuration is changed. For example, the lean / rich determination of the exhaust gas is performed based on the engine operating state. More specifically, the engine control ECU obtains the air-fuel ratio from the ratio between the intake air amount and the fuel injection amount, and performs lean / rich exhaust gas determination based on the obtained air-fuel ratio. In this case, unlike the above embodiments, even when oxygen is supplied to the porous diffusion layer 101 at the time of rich gas and the oxygen deficiency state in the diffusion layer 101 is released, it is not erroneously determined that the gas is lean gas. Absent.
Therefore, it is not necessary to prevent the hunting by defining the lower limit value of the applied voltage of the pump cell. For example, the applied voltage may be set in a negative voltage range. However, the pump cell applied voltage is set within a voltage range that may be applied to zirconia (solid electrolyte), and its lower limit is about -1V.

In addition to a sensor having a two-cell structure, the present invention can be applied to a gas concentration sensor having a three-cell structure and a gas concentration sensor having four or more cells by dividing a plurality of pump cells or sensor cells. Further, in the gas concentration sensor according to the above embodiment, the porous diffusion layer is used as the gas introduction part, but the gas introduction part is not limited to this configuration, and the gas introduction part is configured by a slit or a through hole. May be.

The present invention is applicable not only to a gas concentration sensor capable of detecting the oxygen concentration and the NOx concentration, but also to a gas concentration sensor capable of detecting the oxygen concentration and the HC concentration or the CO concentration. When detecting the HC concentration or the CO concentration, surplus oxygen in exhaust gas (gas to be detected) is discharged by a pump cell, and HC or CO is decomposed from gas components after discharging the surplus oxygen by a sensor cell. Thus, the HC concentration or the CO concentration can be detected in addition to the oxygen concentration.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a gas concentration detection device according to a first embodiment.

FIG. 2 is a configuration diagram of a pump voltage command circuit.

FIG. 3 is a flowchart showing an applied voltage control subroutine.

FIG. 4 is a time chart for explaining the operation of the gas concentration detection device.

FIG. 5 is a diagram showing a relationship between a pump cell applied voltage at the time of rich gas and a response delay time at the time of return of lean gas.

FIG. 6 is an overall configuration diagram of a gas concentration detection device according to a second embodiment.

FIG. 7 is a graph showing a pump cell output characteristic of a gas concentration sensor.
-I diagram.

FIG. 8 is a flowchart showing an applied voltage control subroutine.

FIG. 9 is a sectional view of a main part showing a configuration of a gas concentration sensor.

FIG. 10 is a diagram for explaining the operation principle of the gas concentration sensor.

FIG. 11 is a VI diagram showing pump cell output characteristics of the gas concentration sensor.

FIG. 12 is a VI diagram showing sensor cell output characteristics of the gas concentration sensor.

[Explanation of symbols]

100, 150: Gas concentration sensor, 110, 160: Pump cell as first cell, 120, 170: Sensor cell as second cell, 101: Porous diffusion layer as gas introduction part, 102: Atmosphere as reference gas chamber Duct, 2
11, 251 pump voltage command circuit, 223 current detection circuit, 230 power supply circuit, 240 comparison circuit, 300
Switch circuit.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01N 27/46 327C (72) Inventor Keigo Mizutani 14 Iwatani, Shimowasumicho, Nishio-shi, Aichi Japan Automotive Parts Co., Ltd. Within the Research Institute (72) Inventor Taisuke Makino 14 Iwatani, Shimowakaku-cho, Nishio-shi, Aichi Prefecture Inside the Japan Automobile Parts Research Institute (72) Inventor Toshitaka Saito 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Within DENSO Corporation

Claims (6)

[Claims] 1. A gas introducing part for introducing a gas to be detected, and a pair of electrodes provided so as to sandwich a solid electrolyte, and a surplus in the gas to be detected in the gas introducing part with application of a voltage to the electrodes. It has a first cell for discharging a current according to the oxygen concentration while discharging oxygen, and a pair of electrodes similarly provided so as to sandwich a solid electrolyte, and from a gas component after discharging excess oxygen with application of a voltage to the electrodes. A gas concentration sensor using a gas concentration sensor including a second cell for flowing a current corresponding to the concentration of a specific component, wherein a detection means for detecting that the gas to be detected is a rich gas; When it is detected that the first cell is present, the first cell is controlled so as to suppress the discharge of oxygen from the gas inlet by the first cell.
A gas concentration detection device, comprising: control means for controlling a voltage applied to a cell. 2. A gas concentration detecting device for setting an applied voltage of a first cell in a positive region when a gas to be detected is a lean gas, wherein the control is performed when it is detected that the gas to be detected is a rich gas. The means for applying a voltage to the first cell that is lower than the voltage applied to the first cell set at the time of lean gas.
3. The gas concentration detection device according to 1. 3. The gas concentration detection device according to claim 2, wherein the control means is configured to control the first gas concentration according to a degree of richness of the gas to be detected.
A gas concentration detection device that controls an applied voltage of a cell and reduces the applied voltage of the first cell as the degree of richness increases. 4. The gas concentration detecting device according to claim 2, wherein said control means is set at a time of a lean gas, in addition to a power supply for applying a voltage to said first cell when said gas to be detected is a lean gas. A gas detection concentration device having another power supply having a voltage lower than the voltage applied to the first cell, and switching the power supply of the first cell to the another power supply when the gas to be detected is detected as a rich gas. 5. The gas concentration detection device according to claim 1, wherein the control unit stops applying a voltage to the first cell when the gas is rich. 6. The detecting means according to claim 1, wherein the first or second cell is provided between the reference gas chamber and the gas introduction unit in accordance with an electromotive force of the cell generated when oxygen in the gas introduction unit becomes starved. The detection means detects that the detection gas is a rich gas, and when the gas to be detected is detected as a rich gas, the control means operates in a voltage setting range where the oxygen deficiency state is not released. The gas concentration detecting device according to claim 1, wherein an applied voltage of one cell is set.