JP2002181771A - Controller and method for controlling heater of oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller and method for controlling the heater of an oxygen sensor by which the temperature of the oxygen sensor can be maintained accurately at a preset prescribed value by adjusting the driving voltage of the heater to the voltage value corresponding to the optimum temperature value without using any additional structural parts. SOLUTION: The controller is composed of a variable power source E2, a current detecting section 21, an arithmetic section 22, and an adjusting section 23. The power source E2 impresses the driving voltage upon the heater 15 of the oxygen section 10. The current detecting section 21 detects the current flowing to the heater 15. The arithmetic section 22 calculates the static resistance value of the heater 15 at a room temperature and a plurality of dynamic resistance values of the heater 15 when different voltages are impressed upon the heater 15 based on the voltage value from the power source E2 and current value from the current detecting section 21 and decides the optimum driving voltage of the heater 14 corresponding to the optimum operating temperature value. The adjusting section 23 adjusts the power source E2 to the optimum driving voltage decided by means of the arithmetic section 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater control device and control method for an oxygen sensor for controlling heating of a heater of an oxygen sensor.

[0002]

2. Description of the Related Art A limiting current type oxygen sensor generally comprises a heater section for maintaining an operating temperature and a sensor plate section for exhibiting sensor characteristics. As an example of the limiting current type oxygen sensor, there is a sensor having a structure in which a thermocouple section for detecting the temperature of the sensor plate section is provided in addition to the heater section and the sensor plate section (for example, Japanese Patent Application Laid-Open No. 61-124882). Gazette). In such a structure, an output voltage appears on the detector due to the electromotive force generated in the thermocouple portion, and the output voltage corrects, for example, the applied voltage of the sensor plate portion or controls the heater portion, Temperature correction of the sensor output is possible.

[0003]

However, the oxygen sensor having the above-described structure requires an electrode for connecting to the additional thermocouple, so that the number of electrodes increases and the assemblability deteriorates. Become.

In view of the above, the present invention adjusts the driving voltage of the heater to a voltage value corresponding to the optimum temperature value without additional structural parts, thereby accurately adjusting the temperature of the oxygen sensor. An object of the present invention is to provide a heater control device and a control method for an oxygen sensor that can maintain a predetermined temperature.

[0005]

According to a first aspect of the present invention, there is provided a variable power supply for applying a drive voltage to a heater of an oxygen sensor, and a current detection for detecting a current flowing through the heater. And calculating a static resistance value of the heater at room temperature and a plurality of dynamic resistance values when different heater voltages are applied, based on the voltage value of the variable power supply and the current value from the current detection unit. A calculating unit that determines an optimum driving voltage corresponding to an optimum operating temperature value based on the obtained static resistance value and dynamic resistance value, and adjusts the variable power supply to the optimum driving voltage determined by the calculating unit. And an adjusting unit.

According to the first aspect of the invention, the driving voltage of the heater is adjusted to the optimum driving voltage value corresponding to the optimum operating temperature value without additional structural parts, and the temperature of the oxygen sensor is accurately adjusted to the optimum operating temperature. Can be kept.

According to a second aspect of the present invention, in the oxygen sensor, the solid electrolyte having oxygen ion conductivity, an electrode pair provided on at least a part of both surfaces of the solid electrolyte, and the solid electrolyte being provided on one surface of the solid electrolyte. 2. The oxygen sensor according to claim 1, further comprising: an oxygen gas rate controlling member provided to sandwich one of the electrode pairs to supply diffusion-limited oxygen gas; and a heater for heating the solid electrolyte. In the heater control device.

According to the second aspect of the present invention, the temperature of the solid electrolyte can be maintained at the optimum operating temperature.

According to a third aspect of the present invention, a step of calculating a static resistance value of the heater of the oxygen sensor at room temperature, a step of calculating a plurality of dynamic resistance values of the heater of the oxygen sensor when different heater voltages are applied, Calculating a heater temperature when a different heater voltage is applied based on the static resistance value and the dynamic resistance value; and optimal driving corresponding to an optimum operating temperature value based on the different heater voltage value and the calculated heater temperature value A method of controlling a heater for an oxygen sensor, comprising: calculating a voltage; and adjusting a drive voltage of the heater to the calculated optimum drive voltage.

According to the third aspect of the invention, the driving voltage of the heater is adjusted to the optimum driving voltage value corresponding to the optimum operating temperature value, and the temperature of the oxygen sensor can be accurately maintained at the optimum operating temperature.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a heater control device and control method for an oxygen sensor according to the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an oxygen concentration detecting device incorporating an embodiment of an oxygen sensor heater control device according to the present invention. In the oxygen sensor 10, a porous anode electrode 12a and a cathode electrode 12b (= electrode pair) made of platinum or the like are provided on at least a part of both surfaces of the solid electrolyte 11 made of stabilized zirconia. On one surface, an alumina porous substrate 13 is provided as an oxygen gas rate controlling member for supplying diffusion-controlled oxygen gas with the cathode electrode 12b interposed therebetween.
Then, the solid electrolyte 11 is provided on the alumina porous substrate 13.
The heater 15 is provided for heating the substrate to 400 [° C.] or more to improve the conductivity of oxygen ions.

A direct-current power supply E1 for applying a voltage is connected to the anode electrode 12a and the cathode electrode 12b of the oxygen sensor 10, respectively.
The DC power supply unit E1 is connected in series with a current detection unit 20 for detecting a current flowing using the conduction of oxygen ions in the solid electrolyte 11 as a carrier.

The heater 15 is connected to a heater control device including a variable power supply E 2, a current detection unit 21, a calculation unit 22, and an adjustment unit 23. That is, a variable power source E2 for applying a drive voltage to the heater 15 and a heater 15
And a current detection unit 21 for detecting a current flowing through the power supply is connected in series. The drive voltage value from the variable power supply E2 and the current value from the current detection unit 21 are input to the calculation unit 22, and the output of the calculation unit 22 is supplied to the adjustment unit 23 that adjusts the drive voltage of the variable power supply E2. I have. Arithmetic unit 22 and adjustment unit 23
Is composed of, for example, a microcomputer.

The operation of the oxygen concentration detecting device having the above configuration will be described below. The oxygen gas controlled by the alumina porous plate 13 is supplied to the solid electrolyte 1 via the cathode electrode 12b.
1 is supplied. At this time, the DC power supply unit E1
When a voltage is applied between the anode electrode 12a and the cathode electrode 12b, the oxygen gas receives electrons supplied from the DC power supply unit E1 at the boundary between the cathode electrode 12b and the solid electrolyte 11, and receives oxygen ions (= O ^2−). Anions). The converted oxygen ions conduct in the solid electrolyte 11 and reach the anode electrode 12a, where
At the interface between the solid electrolyte 2a and the solid electrolyte 11, electrons are emitted and return to oxygen gas again.

The above-mentioned current generated by using oxygen ions conducted in the solid electrolyte 11 as a carrier is saturated when the voltage of a predetermined value or more is applied between the anode electrode 12a and the cathode electrode 12b and exceeds the predetermined current. It does not flow. This is because the supply amount of oxygen gas to the cathode electrode 12b is limited by the alumina porous substrate 13, and the number of oxygen ions serving as current carriers is limited.
The above-mentioned current at the time of saturation is called a limiting current. Since this limit current has a value corresponding to the concentration of the surrounding oxygen gas, it is possible to detect the oxygen concentration by detecting the output current of the oxygen sensor 10 which is the current flowing through the solid electrolyte 11 by the current detection unit 20. it can.

Next, a method of controlling the heater 15 will be described. In the present invention, the heater 15 is deteriorated due to some reason (for example, aging), and its resistance increases.
Even if the driving voltage of the heater 15 is kept constant, the variation in the optimum operating temperature of the solid electrolyte 11 due to the inability to keep the driving temperature of the heater 15 constant can be reduced, and the driving temperature of the heater 15 can be stabilized. Next, the heater control device having the above-described configuration connected to the heater 15 is operated.

That is, the heater controller selects a static resistance value Rs of the heater 15 at room temperature and two heater drive voltage points (preferably, a voltage point near the heater drive voltage corresponding to the optimum operating temperature value). ), The heater driving voltage value corresponding to the optimum operating temperature value is calculated based on these resistance values, and the heater 15 is driven with the calculated heater driving voltage value. To control.

Hereinafter, the control method of the heater 15 will be described with reference to FIG.
This will be described based on the flowchart shown in FIG.

First, the room temperature of the heater 15 (for example, 25 ° C.)
) Is calculated (step S).
1). When calculating the static resistance value Rs, the voltage value of the variable power supply E2 is adjusted by the adjusting unit 23 to prevent the temperature of the heater 15 from rising due to the voltage application itself.
It is desirable to adjust the voltage to about 1/100 or less.
In this example, since the static resistance value of the heater 15 is about 5 to 6 ohms, the voltage value of the variable power source E2 is set to 0.05 volt (=
The static resistance value Rs at room temperature is calculated by adjusting to 50 mV).

Next, the adjusting section 23 applies, for example, 6.0 volts to the heater 15 as a predetermined first heater drive voltage V1 with the voltage value of the variable power supply E2, and the dynamic resistance of the heater 15 at that time is applied. The calculation unit 22 calculates the value R1 based on the current value I1 detected by the current detection unit 21 and the applied voltage value V1 (step S2). Next, the adjusting unit 23
For example, 6.5 volts is applied to the heater 15 as a predetermined second heater drive voltage V2 with the voltage value of the variable power supply E2, and the dynamic resistance value R2 of the heater 15 at that time is applied.
Is calculated by the calculation unit 22 based on the current value I2 and the applied voltage value V2 detected by the current detection unit 21 (step S
3).

The heater 1 of the oxygen sensor 10 used here
The TCR temperature coefficient α of 5 is known in advance depending on the material of the heater 15, and is set to, for example, α = 0.0036. Therefore, next, using the temperature coefficient α, the operating unit 22 calculates the operating temperature T1 of the heater 15 when V1 = 6.0 volts is applied, based on the following equation (1) (step S4).

T1 = {R1 × (1 + 0.0036 × 25) −Rs} / (0.0036 × Rs) (1)

Next, using this temperature coefficient α, V2 = 6.
The operation unit 22 calculates the operating temperature T2 of the heater 15 when 5 volts is applied based on the following equation (2) (step S2).
5).

T2 = {R2 × (1 + 0.0036 × 25) −Rs} / (0.0036 × Rs) (2)

Next, since the heater driving voltage and the operating temperature are in a proportional relationship, the operating temperatures T1 and T2 obtained by the above equations (1) and (2) and the heater driving voltage values V1 and V2 are simultaneously set. , The optimal driving voltage value Vm corresponding to the optimal operating temperature Tm
Is calculated based on the following equation (3) or (4) (step S6).

Vm = {(V2−V1) / (T2−T1)} × (Tm−T1) + V1 (3)

Vm = {(V2−V1) / (T2−T1)} × (Tm−T2) + V2 (4)

Next, the optimum driving voltage value Vm obtained by the equation (3) or (4) is inputted from the calculating section 22 to the adjusting section 23, and the adjusting section 23 adjusts the voltage of the variable power source E2 to the above-mentioned optimum driving voltage. Adjustment is made so that the voltage value becomes Vm.

Here, a specific calculation example will be described.
5.58 ohm, R1 = 15.90 ohm, R2 = 1
At 6.56 ohms, T1 =
585 ° C. and T2 = 621 ° C.

Therefore, for example, when the optimum operating temperature value is 6
If the temperature is 30 ° C., the optimum driving voltage value V corresponding to this temperature
m ₆₃₀ is determined by equation (4).

Vm ₆₃₀ = {(6.5-6.0) / (621-585)} × (630-621) + 6.5 = 6.63 (volts)

Therefore, by adjusting the voltage of the variable power supply E2 to 6.63 volts by the adjusting unit 23, the temperature of the heater 15 becomes 630 ° C., and the oxygen sensor 10 can be heated to the optimum operating temperature.

As described above, by obtaining the static resistance value Rs of the heater 15 at room temperature and the two dynamic resistance values R1 and R2 at two heater drive voltage points, the optimum operation of the oxygen sensor 10 is finally achieved. The temperature can be maintained at 630 ° C.

As described above, the embodiment of the present invention has been described. However, the present invention is not limited to this, and various modifications and applications are possible.

For example, the control method of the heater 15 described in the above embodiment is automatically performed at the same time as the atmospheric calibration (which is well known in the art and the description is omitted here) in the oxygen concentration detecting apparatus of FIG. You may be comprised so that it may be performed. In this case, even when the static resistance value Rs of the heater 15 of the oxygen sensor 10 changes due to some reason (for example, a change over time) during use of the oxygen concentration detection device, and the operating temperature fluctuates from the optimum operating temperature, calibration is always performed. The subsequent operating temperature can be calibrated to the optimal operating temperature. This also makes it possible to suppress a decrease in operating temperature due to heater deterioration.

[0037]

As described above, according to the first aspect of the present invention, the driving voltage of the heater is adjusted to a voltage value corresponding to the optimum operating temperature value without additional structural parts, and the temperature of the oxygen sensor is adjusted. Can be accurately maintained at the optimum operating temperature.

According to the second aspect of the present invention, the temperature of the solid electrolyte can be maintained at the optimum operating temperature.

According to the third aspect of the invention, the driving voltage of the heater is adjusted to a voltage value corresponding to the optimum operating temperature value, and the temperature of the oxygen sensor can be accurately maintained at the optimum operating temperature.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an oxygen concentration detection device incorporating one embodiment of a heater control device for an oxygen sensor according to the present invention.

FIG. 2 is a flowchart showing a control method of a heater of the oxygen sensor in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Solid electrolyte 12a Anode electrode (electrode pair) 12b Cathode electrode (electrode pair) 13 Porous alumina substrate (oxygen gas rate controlling body) 15 Heater 20 Current detection unit (current detection means) 21 Current detection unit 22 Operation unit 23 Adjustment unit E1 DC power supply (DC power supply) E2 Variable power supply

Claims (3)

[Claims] A variable power supply for applying a drive voltage to a heater of the oxygen sensor; a current detection unit for detecting a current flowing through the heater; and a voltage value of the variable power supply and a current value from the current detection unit. Calculating a static resistance value of the heater at room temperature and a plurality of dynamic resistance values when different heater voltages are applied, and corresponding to an optimum operating temperature value based on the calculated static resistance value and dynamic resistance value. An oxygen sensor heater control device, comprising: a calculation unit that determines an optimum drive voltage to be adjusted; and an adjustment unit that adjusts the variable power supply to the optimum drive voltage determined by the calculation unit. 2. The oxygen sensor includes: a solid electrolyte having oxygen ion conductivity; an electrode pair provided on at least a part of both surfaces of the solid electrolyte; and one of the electrode pairs sandwiched on one surface of the solid electrolyte. And a heater for heating the solid electrolyte, the oxygen gas controlling member for supplying oxygen gas diffusion-controlled, and a heater for heating the solid electrolyte.
A heater control device for an oxygen sensor as described in the above. A step of calculating a static resistance value of the heater of the oxygen sensor at room temperature; a step of calculating a plurality of dynamic resistance values of the heater of the oxygen sensor when different heater voltages are applied; Calculating a heater temperature at the time of applying a different heater voltage based on the resistance value; calculating an optimum drive voltage corresponding to the optimum operating temperature value based on the different heater voltage value and the calculated heater temperature value; Adjusting the drive voltage of the heater to the calculated optimum drive voltage. A heater control method for an oxygen sensor, comprising: