JP2004029039A - Method and apparatus for controlling temperature in electromotive force cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature controlling method and a temperature controlling apparatus of a total region oxygen sensor for accurately and constantly maintaining temperature. <P>SOLUTION: A constant current ICONST is applied to an electromotive force cell 24 being pinched between a diffusion chamber 20 in a fixed atmosphere and an oxygen reference chamber 26 in fixed oxygen concentration to measure a resistance value, thus accurately measuring the resistance value regardless of the oxygen concentration in the measurement atmosphere of an oxygen sensor element 10. Additionally, the resistance value of the electromotive force cell 24 is measured at specific timing T2 when current starts to be applied, thus accurately performing measurement without including an amount of change in resistance due to deterioration or the like in porous electrodes 22, 24 in the electromotive force cell 24 being included in measurement by DC. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a temperature control method and a temperature control device for an all-region oxygen sensor that detects the concentration of oxygen contained in exhaust gas of an engine.

An oxygen sensor is provided in the exhaust system to control the air-fuel ratio of the air-fuel mixture supplied to the engine to a target value and reduce CO, NOx, and HC in the exhaust gas. It is known that the fuel supply amount is feedback-controlled according to the concentration. As the oxygen sensor used for this feedback control, there are a λ sensor whose output changes stepwise at a specific oxygen concentration (particularly, a stoichiometric air-fuel ratio atmosphere) and an oxygen sensor whose output continuously changes from a lean region to a rich region. Sensors are mainly used. As described above, the full-range oxygen sensor can continuously measure the oxygen concentration in the exhaust gas, and can improve the speed and accuracy of the feedback control. I have.

In the whole-area oxygen sensor, two cells of an oxygen ion conductive solid electrolyte body are disposed to face each other with a space therebetween, and one of the cells is used as a pump cell that draws oxygen in the space to the surroundings or draws oxygen from the surroundings. Further, the other cell is used as an electromotive force cell that generates a voltage due to a difference in oxygen concentration between the oxygen reference chamber and the space, and the pump cell is operated so that the output of the electromotive force cell becomes constant. Is measured as a measured oxygen concentration proportional value. The operating principle of this full-range oxygen sensor is described in detail in Japanese Patent Application Laid-Open No. Sho 62-148849 filed by the present applicant.

In order to operate this full-area oxygen sensor, it is necessary to heat the pump cell and the electromotive force cell to a predetermined temperature or higher to increase the activity of the oxygen ion conductive solid electrolyte. For this reason, a heater for heating is attached to the whole area oxygen sensor near the pump cell and the electromotive force cell.
JP-A-62-148849

At present, it is required to further reduce harmful gas components such as CO, NOx, and HC in exhaust gas. In order to remove this harmful gas, it is necessary to more accurately measure the oxygen concentration in the exhaust gas with an oxygen sensor and to perform feedback control of the air-fuel ratio at a high speed. Here, in order to improve the accuracy of the oxygen sensor, it is required to keep the temperature of the oxygen sensor constant. In order to achieve a constant temperature, a method has been adopted in which the temperature of the heater is measured by measuring the resistance value of the heater, the measured temperature is regarded as substantially equal to the cell temperature, and the temperature of the heater is kept constant.

However, in this method, when the temperature of the exhaust gas is low or when the flow rate of the gas is high, the cell temperature and the heater temperature do not match, and the cell temperature cannot be controlled with high accuracy.

The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a temperature control method and apparatus for an entire region oxygen sensor that can accurately maintain a constant temperature.

In order to achieve the above object, in the temperature control method for an all-region oxygen sensor according to claim 1, two cells provided with porous electrodes on both surfaces of an oxygen ion conductive solid electrolyte heated by a heater are provided. A pump cell is disposed opposite to a space, and one of the cells is a pump cell that draws oxygen into or draws oxygen in the space, and the other cell generates a voltage due to an oxygen concentration difference between the oxygen reference chamber and the space. A method of controlling the temperature of the two-area oxygen sensor, which is used as an electromotive force cell and measures the oxygen concentration, of the two cells, using the heater for heating,
Apply a constant current or voltage for resistance measurement to the electromotive force cell,
The resistance value of the electromotive force cell is measured within a predetermined time after the application of the current or voltage for resistance measurement so that the resistance value does not include a resistance component at the interface between the porous electrode and the solid electrolyte body. And
The technical feature is that the heater is controlled such that the measured resistance value of the electromotive force cell becomes a constant value.

Furthermore, in claim 2, after measuring the resistance value of the electromotive force cell, following application of the resistance value measurement current or voltage, a constant current or voltage having a polarity opposite to the current or voltage is applied for a predetermined time. It is characterized by applying.

In order to achieve the above object, in the temperature control device for an all-zone oxygen sensor according to claim 3, two cells having porous electrodes provided on both surfaces of an oxygen ion conductive solid electrolyte body heated by a heater are provided. A pump cell is disposed opposite to a space, and one of the cells is a pump cell that draws oxygen into or draws oxygen in the space, and the other cell generates a voltage due to an oxygen concentration difference between the oxygen reference chamber and the space. A temperature control device for an entire-area oxygen sensor, which is used as an electromotive force cell and measures the oxygen concentration of the entire-area oxygen sensor, and controls the temperatures of the two cells by using the heater for heating.
First current or voltage applying means for applying a constant current or voltage for resistance measurement to the electromotive force cell,
The resistance value of the electromotive force cell is measured within a predetermined time after the application of the current or voltage for resistance measurement so that the resistance value does not include a resistance component at the interface between the porous electrode and the solid electrolyte body. Resistance measurement means for performing
After measuring the resistance value of the electromotive force cell, a second current or voltage application for applying a constant current or voltage having a polarity opposite to the current or voltage for a predetermined time following application of the resistance measurement current or voltage. Means,
Temperature control means for controlling the heater so that the measured resistance value of the electromotive force cell becomes a constant value.

In order to achieve the above object, the whole area oxygen sensor of claim 4 is provided with the temperature control device of claim 3.

According to the first aspect of the present invention, since a voltage or a current is applied to an electromotive force cell sandwiched between an interval maintained at a constant atmosphere by a pump cell and an oxygen reference chamber having a constant oxygen concentration to measure a resistance value, The resistance value can be accurately measured irrespective of the oxygen concentration in the measurement atmosphere of the region oxygen sensor. Further, the resistance value of the electromotive force cell is determined at a predetermined timing from the time when the application of voltage and current is started so that the resistance value does not include the resistance component at the interface between the porous electrode and the solid electrolyte body. For the measurement, it does not include the change in the resistance component at the interface due to the deterioration of the interface between the porous electrode and the solid electrolyte body of the electromotive cell included when measured by the low-frequency current or voltage, and The bulk resistance component of the solid electrolyte can be accurately measured. Therefore, a resistance value accurately reflecting the cell temperature can be obtained.

According to the second aspect of the present invention, when applying a voltage to the electromotive force cell, a constant voltage or current having a polarity opposite to that of the current or the voltage is applied following the application of the voltage or the current for resistance measurement. , The internal electromotive force is affected by the orientation phenomenon of the oxygen ion conductive solid electrolyte body that occurs when a large current flows, and the return time from when no internal electromotive force value that reflects the original oxygen concentration difference is output to when the device returns. And the measurement of the oxygen concentration can be resumed in a short time after the measurement of the resistance value.

According to the fourth aspect of the present invention, the resistance value is measured by applying a voltage or a current to an electromotive force cell sandwiched between an interval maintained at a constant atmosphere by a pump cell and an oxygen reference chamber having a constant oxygen concentration. The resistance value can be accurately measured irrespective of the oxygen concentration therein. Further, in order to measure the resistance value of the electromotive force cell so that the resistance value does not include a resistance component at the interface between the porous electrode and the solid electrolyte body, when measured by a low-frequency current or voltage. The bulk resistance component of the solid electrolyte body of the electromotive force cell can be accurately measured without including the change in the resistance component at the interface between the porous electrode of the electromotive cell and the solid electrolyte body due to deterioration of the interface.

According to the temperature control method and apparatus of the whole area oxygen sensor according to claims 1 and 4, a voltage or a current is applied to an electromotive force cell sandwiched between an interval that is an atmosphere having a stoichiometric air-fuel ratio and an oxygen reference chamber that has a constant oxygen concentration. Therefore, the resistance value can be accurately measured irrespective of the oxygen concentration in the measurement atmosphere. Further, in order to measure the resistance value of the electromotive force cell so that the resistance component at the interface between the porous electrode and the solid electrolyte body is not included, the resistance value of the electromotive force cell included when measured by a low-frequency current or voltage is used. The temperature of the sensor element can be accurately measured without being affected by a change in resistance due to deterioration of the interface between the porous electrode and the solid electrolyte body.

According to the second or third aspect of the present invention, when a voltage or current for resistance measurement is applied to the electromotive force cell, the voltage or current for resistance measurement is reversed following the application of the voltage or current for resistance measurement. Since a polarity voltage or current is applied, the internal electromotive force is affected by the orientation phenomenon of the oxygen ion conductive solid electrolyte body, and the internal electromotive force value that reflects the original oxygen concentration difference is not output. The return time until the return can be shortened, and the measurement of the oxygen concentration can be restarted in a short time after the measurement of the resistance value.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a full area oxygen sensor according to one embodiment of the present invention. The cell 10 is provided in an exhaust gas system. The cell 10 is connected to a controller 50 that measures the oxygen concentration in the exhaust gas and the temperature of the cell 10. A heater 70 controlled by a heater control circuit 60 is attached to the cell 10 via a ceramic bonding agent (not shown). The heater 70 is made of ceramic such as alumina as an insulating material, and has a heater wiring 72 disposed therein. The heater control circuit 60 applies electric power to the heater 70 so as to keep the resistance value of the cell 10 measured by the controller 50 at a target value, and maintains the temperature of the cell 10 at a set value.

The cell 10 is configured by stacking a pump cell 14, a porous diffusion layer 18, an electromotive force cell 24, and a reinforcing plate 30. The pump cell 14 is made of stabilized or partially stabilized zirconia (ZrO2), which is an oxygen ion conductive solid electrolyte material, and has porous electrodes 12, 16 mainly made of platinum on its front and back surfaces, respectively. I have. The porous electrode 12 on the front side exposed to the measurement gas is referred to as an Ip + electrode because an Ip + voltage is applied to flow an Ip + current. The back side porous electrode 14 is referred to as an Ip-electrode because an Ip-voltage is applied to flow an Ip current.

Similarly, the electromotive force cell 24 is also formed of stabilized or partially stabilized zirconia (ZrO2), and has porous electrodes 22, 28 mainly formed of platinum on the front and back surfaces, respectively. The porous electrode 18 disposed on the diffusion chamber 20 side is referred to as a Vs-electrode because a Vs-voltage of the electromotive force Vs of the electromotive force cell 24 is generated, and the porous electrode 18 disposed on the reference oxygen chamber 26 side. The quality electrode 28 is referred to as a Vs + electrode because a Vs + voltage is generated. The reference oxygen in the reference oxygen chamber 26 is generated by pumping constant oxygen from the porous electrode 22 to the porous electrode 28. A diffusion chamber 20 surrounded by the porous diffusion layer 18 is formed between the pump cell 14 and the electromotive force cell 24. That is, the diffusion chamber 20 is communicated with the measurement gas atmosphere via the porous diffusion layer 18. In this embodiment, the porous diffusion layer 18 filled with a porous substance is used. However, a small hole may be provided instead.

Here, oxygen according to the difference between the oxygen concentration of the measurement gas and the oxygen concentration in the diffusion chamber 20 diffuses toward the diffusion chamber 20 via the porous diffusion layer 18. Here, when the atmosphere in the diffusion chamber 20 is maintained at the stoichiometric air-fuel ratio, the Vs + electrode 28 and the Vs- electrode of the electromotive force cell 24 are located between the diffusion chamber 20 and the reference oxygen chamber 26 in which the oxygen concentration is kept substantially constant. 22 and a potential of about 0.45 V is generated. For this reason, the controller 50 maintains the atmosphere in the diffusion chamber 20 at the stoichiometric air-fuel ratio by adjusting the current Ip flowing through the pump cell 14 so that the electromotive force Vs of the electromotive force cell potential 24 becomes 0.45 V. The oxygen concentration in the measurement gas is measured based on the pump cell current amount Ip for maintaining the stoichiometric air-fuel ratio.

Subsequently, the control operation will be described with reference to FIG.
The controller 50 performs an operation of measuring the oxygen concentration using the cell 10 and an operation of measuring the temperature by measuring the bulk resistance of the electromotive force cell 24 of the cell 10. Here, the oxygen concentration measurement will be described first.

In the operational amplifier OP2, +4 V is applied to one input terminal, and the other input terminal is connected to the VCENT point. Even if the Ip current flowing through the pump cell 14 changes at the output terminal, the operation amplifier OP2 is connected to the VCENT point. And operates to keep it at 4V. The PID circuit that performs PID control detects the electromotive force Vs of the electromotive force cell 24 and determines the current Ip of the pump cell 14 so as to keep Vs constant (0.45 V) by the Ip current flowing through the resistor R1. Do. As described above, in a state where the electromotive force of the electromotive force cell 24 is maintained at 0.45 V in the PID circuit, a voltage proportional to the amount of the current Ip flowing through the pump cell 14 appears at the output terminal of the PID circuit. Is converted into a digital value by an A / D circuit (not shown) in an oxygen concentration detection circuit 52, and a corresponding oxygen concentration value is searched from a held map, and this value is output to an engine control device (not shown). .

Subsequently, the operation of measuring the temperature (resistance) of the electromotive force cell 24 of the controller 50 will be described. The operational amplifier OP1 forms a sample-and-hold circuit together with the capacitor C1, and holds the electromotive force Vs of the electromotive force cell 24 immediately before the voltage is applied during the voltage application for measuring the temperature of the electromotive force cell 24 and inputs the voltage to the PID circuit. Fulfill. The operational amplifier OP3 applies the hold value (the electromotive force Vs of the electromotive force cell 24 immediately before the application of the resistance value measuring voltage) held in the operational amplifier OP1 and the current −Iconst for the resistance value measurement to the electromotive force cell 24. Is output to the A / D circuit.

The switch SW1 controls the operational amplifier OP1, that is, the sample-and-hold circuit voltage hold operation. The switch SW2 turns on and off a constant current -Iconst for measuring the resistance value of the electromotive force cell 24, and the switch SW3 has a constant polarity opposite to the current -Iconst for measuring the resistance value flowing through the switch SW2. Turns on / off the current + Iconst.

FIG. 3 shows the electromotive force Vs of the electromotive force cell 24 together with the timing chart of the switches SW1, SW2, and SW3. The switch SW1 is turned off for the time T6 (about 500 μs) set at every predetermined interval T5 as described above, thereby enabling the resistance measurement of the electromotive force cell 24. During the off time T6, the input value to the PID circuit is maintained at 0.45 V by the sample and hold circuit including the operational amplifier OP1.

(4) After the time T1 has elapsed since the switch SW1 was turned off, the switch SW2 is turned on for a time T3 (about 100 μs), and a constant current -Iconst for measuring the resistance value flows to the electromotive force cell 24 side. The polarity of the current -Iconst is opposite to the polarity of the internal electromotive force generated in the electromotive force cell 24, and the voltage at both ends of the electromotive force cell 24 decreases by ΔVs as shown in FIG.

Here, after the application of the current -Iconst is started, after the time T2 (about 60 μs) has elapsed, the output of the operational amplifier OP3 at the time (60 μs after the start of application) is converted into an analog signal by the A / D conversion circuit. The value is converted into a digital value and output to the heater control circuit side 60. The heater control circuit 60 controls energization of the heater 70 so that the measured value, that is, a value correlated with the bulk resistance value of the electromotive force cell 24 becomes a target value. This control substantially raises the voltage when the bulk resistance value of the electromotive force cell 24 is higher than the target value, and lowers the voltage when the bulk resistance value is lower than the target value, thereby accurately controlling the temperature of the oxygen sensor element 10. At the target temperature (800 ° C.).

Here, the value at the time when 60 μs elapses from the start of application of the current −Iconst is measured so that the measured resistance value does not include the resistance component at the interface between the porous electrode and the solid electrolyte body. That's why. This is because when measurement is performed using low-frequency current or voltage, a value including a change in the resistance component at the interface between the porous electrodes 22, 28 of the electromotive force cell 24 and the solid electrolyte body due to deterioration or the like is detected. Therefore, the measurement cannot be performed accurately due to the change. Conversely, by changing the time of this measurement, the resistance including the deterioration can be measured and used for deterioration detection.

When the time T3 elapses, the switch SW2 is turned off, and at the same time, the switch SW3 is turned on. Over a time T3 substantially equal to the time when the switch SW2 is turned on, the current -Iconst having a polarity opposite to that of the current for measuring the resistance is kept constant. The current + Iconst is applied to the electromotive force cell 24 side. This is because the internal electromotive force is affected by the orientation phenomenon of the oxygen ion conductive solid electrolyte constituting the electromotive force cell 24 and the internal electromotive force value that reflects the original oxygen concentration difference is not output, but changes to a normal state. This is because the return time before the return is shortened, and the measurement of the oxygen concentration can be restarted in a short time after the measurement of the resistance value.

{Return time to normal electromotive force, which is considered to be an orientation phenomenon of the oxygen ion conductive solid electrolyte body, will be described with reference to FIG. FIG. 4A shows the electromotive force of the electromotive force cell when a current of 4.88 mA corresponding to the current -Iconst for measuring the resistance value is applied to the electromotive force cell 24 in the form of a pulse, and then the current is stopped. FIG. 4B shows a change in Vs. FIG. 4B shows that after applying a current of 4.88 mA corresponding to the current -Iconst in a pulse shape, a current + Iconst having a polarity opposite to -Iconst of the current is generated in a pulse shape. The graph shows a change in the electromotive force Vs of the electromotive force cell when applied to the cell 24, that is, when applied in an alternating manner. As shown in FIG. 4A, in the case where a current of 4.88 mA was applied only once in a pulse form, it took 16 msec to recover. On the other hand, when the current was alternately applied as shown in FIG. 4 (B), it was possible to recover in 0.5 msec. As described above, in this embodiment, the measurement of the oxygen concentration using the electromotive force cell 24 can be restarted in a short time by applying the current alternately.

After a lapse of time T3 for applying the constant current + Iconst, the switch SW3 is turned off, and then, at the timing of lapse of time T4, the switch SW1 is turned on and the electromotive force Vs of the electromotive force cell 24 is again changed to the operational amplifier. It is added to the PID circuit via OP1, and the measurement of the oxygen concentration is restarted. Then, after the elapse of the interval T5, the switch SW1 is turned off, and the resistance value of the electromotive force cell 24 is measured again.

In this embodiment, the temperature of the cell 10 is measured by measuring the resistance value of the electromotive force cell 24 instead of the pump cell 14. This operation will be described with reference to the graph of FIG. FIG. 5A is a graph when an AC current is applied to the electromotive force cell 24 and the resistance is measured. FIG. 5B is a graph when an AC is applied to the pump cell 14 and the resistance is measured. It is a graph at the time of measurement. In the figure, the vertical axis represents the measured resistance value, and the horizontal axis represents the heater voltage corresponding to the cell 10 temperature. Here, ○ indicates a value measured at 20 Hz (low frequency) in an A / F23 (lean state) atmosphere, and ● indicates a value measured at 1 KHz (high frequency) in an A / F23 (lean state) atmosphere. Δ is a value measured at 20 Hz (low frequency) in an atmosphere of stoichiometric air-fuel ratio, and Δ is a value measured at 1 KHz (high frequency) in an atmosphere of stoichiometric air-fuel ratio. Indicates the value.

In the graph of FIG. 5A corresponding to the present embodiment, the resistance value measured in an atmosphere having a stoichiometric air-fuel ratio is substantially equal to the resistance value measured in a lean atmosphere, and the resistance value is accurate regardless of the oxygen reference chamber. It can be seen that the resistance can be measured. On the other hand, in the graph of FIG. 5B, the resistance value measured in the atmosphere of the stoichiometric air-fuel ratio is different from the resistance value measured in the lean atmosphere, and the resistance value is accurately determined by the oxygen reference chamber. It turns out that measurement is not possible. This is because, when a current is applied to the electromotive force cell 24 (see FIG. 1), the electromotive force cell 24 is connected to the diffusion chamber 20 fixed in an atmosphere having a stoichiometric air-fuel ratio and the oxygen reference chamber having a constant oxygen concentration. 26, the oxygen concentration on both sides of the electromotive force cell is always constant. On the other hand, the pump cell 14 is sandwiched between the measurement gas in which the oxygen concentration is changing and the diffusion chamber 20 fixed in the atmosphere of the stoichiometric air-fuel ratio. This is because it always varies depending on the oxygen concentration.

It is an explanatory view showing the whole area oxygen sensor composition concerning one embodiment of the present invention. FIG. 2 is a circuit diagram of the controller shown in FIG. 1. 5 is a timing chart of switches SW1, SW2, and SW3. FIG. 4 (A) shows the electromotive force cell electromotive force Vs when the resistance value measuring current is applied once to the electromotive force cell in a pulse shape, and FIG. 4 (B) shows the case where the current is applied alternately. The electromotive force Vs of the electromotive force cell shown in FIG. FIG. 5A is a graph in which an AC current is applied to the electromotive force cell to measure the resistance value, and FIG. 5B is a graph in which an AC current is applied to the pump cell to measure the resistance value.

Explanation of reference numerals

Reference Signs List 10 cell 14 pump cell 20 diffusion chamber 24 electromotive cell 50 controller 60 heater control circuit 70 heater Vs electromotive cell voltage Ip pump cell current

Claims (4)

Two cells having porous electrodes provided on both sides of an oxygen ion conductive solid electrolyte body heated by a heater are disposed to face each other with an interval therebetween, and one of the cells is provided with oxygen in the interval surrounding the cell. A pump cell for pumping or pumping oxygen, and the other cell being used as an electromotive force cell for generating a voltage due to a difference in oxygen concentration between the oxygen reference chamber and the interval, and an oxygen sensor for measuring the oxygen concentration in the whole area. A method for controlling the temperature of a cell, which controls the temperature of an entire-area oxygen sensor using the heater for heating,
Apply a constant current or voltage for resistance measurement to the electromotive force cell,
The resistance value of the electromotive force cell is measured within a predetermined time after the application of the current or voltage for resistance measurement so that the resistance value does not include a resistance component at the interface between the porous electrode and the solid electrolyte body. And
A temperature control method for an oxygen sensor for an entire area, wherein the heater is controlled so that the measured resistance value of the electromotive force cell becomes a constant value. After measuring the resistance value of the electromotive force cell, a constant current or voltage having a polarity opposite to that of the current or voltage is applied for a predetermined time following application of the resistance measurement current or voltage. The method for controlling the temperature of an entire-area oxygen sensor according to claim 1. Two cells having porous electrodes provided on both sides of an oxygen ion conductive solid electrolyte body heated by a heater are disposed to face each other with an interval therebetween, and one of the cells is provided with oxygen in the interval surrounding the cell. A pump cell for pumping or pumping oxygen, and the other cell being used as an electromotive force cell for generating a voltage due to a difference in oxygen concentration between the oxygen reference chamber and the interval, and an oxygen sensor for measuring the oxygen concentration in the whole area. A temperature control device for an entire-area oxygen sensor that controls the temperature of the cell using the heater for heating,
First current or voltage applying means for applying a constant current or voltage for resistance measurement to the electromotive force cell,
The resistance value of the electromotive force cell is measured within a predetermined time after the application of the current or voltage for resistance measurement so that the resistance value does not include a resistance component at the interface between the porous electrode and the solid electrolyte body. Resistance measurement means for performing
After measuring the resistance value of the electromotive force cell, a second current or voltage application for applying a constant current or voltage having a polarity opposite to the current or voltage for a predetermined time following application of the resistance measurement current or voltage. Means,
Temperature control means for controlling the heater so that the measured resistance value of the electromotive force cell becomes a constant value. A full range oxygen sensor comprising the temperature control device according to claim 3.

Images