JP3035063B2 - Oxygen sensor temperature control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the temperature of an oxygen sensor with a heater.

[0002]

2. Description of the Related Art Conventionally, in order to measure the oxygen concentration in a mixed gas of an internal combustion engine and the oxygen concentration in exhaust gas of an incinerator,
An oxygen sensor with a heater is used. This oxygen sensor with a heater is configured integrally with an oxygen sensor capable of measuring the oxygen concentration using the ionic conductivity of a solid electrolyte such as zirconia, and a heater for heating the oxygen sensor. The heater is controlled by a temperature control device including a unit for measuring an applied voltage of the heater unit, a unit for measuring a current flowing through the heater unit, a heater power control device, and a calculation unit, thereby providing an oxygen sensor. Is controlling the temperature.

When an oxygen sensor having the above-described structure is mounted on a predetermined position such as a flue of a plant for measurement, the oxygen sensor is maintained at a certain temperature after the oxygen sensor is mounted, depending on the temperature of the flue wall and the temperature of exhaust gas. Therefore, once it is attached, it is not possible to directly measure, for example, a normal temperature resistance value required for control. Therefore, before mounting the oxygen sensor, for example, by measuring the resistance of the sensor at normal temperature in a resistance range of a digital voltmeter and inputting the value to a temperature control device and using the same, the temperature control of the heater and, consequently, the oxygen sensor can be performed. Temperature control was implemented.

[0004]

However, the conventional apparatus described above has a problem that the ordinary temperature resistance value measured by key input must be input every time the oxygen sensor is replaced, which is troublesome and inefficient. In addition, there is a problem that mistakes at the time of key input are likely to occur particularly when the number of oxygen sensors is increased. In addition, since it often undergoes thermal cycling, the room temperature resistance value changes with time,
There is also a problem that the temperature control cannot be suitably performed when the normal temperature resistance value input first is used.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a temperature control method of an oxygen sensor that can obtain a normal temperature resistance value without error by a simple method and can perform suitable temperature control.

[0006]

According to the present invention, there is provided a temperature control method for an oxygen sensor, comprising: means for measuring a voltage applied to a heater of an oxygen sensor; means for measuring a current flowing through a heater of the oxygen sensor; In the method of controlling the temperature of the oxygen sensor by the temperature control device including the control device and the calculating means, when the power of the heater power control device is turned on, the following steps 1 to 3 are performed to execute the normal temperature heater resistance RH0. And the heater applied voltage VH and heater current IH
And the heater resistance RH = VH / IH is calculated, and the ratio RH / R between the heater resistance RH and the normal temperature heater resistance RH0 is calculated.
The heater power is controlled so that the temperature of the oxygen sensor becomes constant, using H0 as the temperature signal of the sensor. Step 1: After applying the first applied voltage VH1 to the heater, the heater current IH1 is measured, and the heater resistance RH1 =
Calculate VH1 / IH1. Step 2: After applying the second applied voltage VH2 to the heater, the heater current IH2 is measured, and the heater resistance RH2 =
VH2 / IH2 is calculated, and the heater supply power PW2 = VH
Calculate 2 * IH2. Step 3: From the obtained RH1, RH2, and PW2, the normal-temperature heater resistance RH0 = K1 * RH1 / RH2 + K2 * P
Calculate W2 + B. (However, K1, K2, and B are constants previously determined based on the shape of the oxygen sensor.)

[0007]

In the above-described configuration, the normal temperature resistance value of the heater used for controlling the temperature of the heater can be obtained by the calculation based on the above steps 1 to 3.
If the same PID control as that of the related art is performed based on the normal temperature resistance value, it is possible to perform suitable heater temperature control without troublesome measurement such as actual measurement at the time of mounting and without input error. As a result, the measurement accuracy of the oxygen sensor can be kept high.

[0008]

FIG. 1 is a block diagram showing a specific example of a method for controlling the temperature of an oxygen sensor according to the present invention. In FIG. 1, reference numeral 1 denotes a heater section of an oxygen sensor (not shown);
Is a temperature control device for controlling the temperature of the heater section 1. The temperature control device 2 includes a heater current measuring unit 11 for measuring a heater current IH flowing through the heater unit 1, a heater voltage measuring unit 12 for measuring a voltage VH applied to the heater unit 1, a measured heater current IH and a heater. An arithmetic unit 13 for performing the control of the present invention from the voltage VH, and a power control PWM device 1
A heater power control device 15 for controlling the power supplied to the heater section 1 based on the result of the arithmetic unit 13 supplied via the AC power supply 4 and an AC / DC converter for converting a 100 V AC commercial power supply to a DC of a predetermined voltage. DC converters 16 and 17 are provided. The arithmetic unit 13 is provided with a normal temperature resistance measurement switch 21 and a power switch 22.

FIG. 2 is a flowchart showing an example of a method for controlling the temperature of the oxygen sensor implemented in the apparatus shown in FIG. The temperature control method according to the present invention will be described with reference to FIG. 2. First, an oxygen sensor installed in a flue of a plant or the like is kept at a constant temperature. After this state,
Power switch 2 while pressing normal temperature resistance measurement switch 21
2 are simultaneously turned on, and a normal temperature resistance measurement flag is set. Thereafter, steps 1 to 3 described in detail below are performed to determine the normal temperature resistance value RH0 of the heater. Thereafter, the normal-temperature resistance measurement flag is lowered in the arithmetic unit 13. Thereafter, the same apparatus performs the same temperature adjustment processing as that of the related art based on the obtained normal temperature resistance value RH0.

Hereinafter, steps 1 to 3 in the arithmetic unit for determining the normal temperature resistance value of the heater in the method of controlling the temperature of the oxygen sensor according to the present invention will be described. First,
In Step 1, after applying the first applied voltage VH1 to the heater for T1 minutes, the heater current IH1 is measured, and the heater resistance RH1 = VH1 / IH1 is calculated. Next, as a step 2, after applying the second applied voltage VH2 to the heater for T2 minutes, the heater current IH2 is measured, the heater resistance RH2 = VH2 / IH2 is calculated, and the heater supply power P
Calculate W2 = VH2 * IH2. Finally, step 3
From the obtained RH1, RH2, and PW2, the normal temperature heater resistance RH0 = K1 * RH1 / RH2 + K2 * PW2
+ B is calculated. Here, assuming that the thermal time constant of the sensor is Tc, the time of TH1 is preferably 5 to 15 Tc seconds, and the time of TH2 is preferably 5 to 15 Tc seconds for thermal stability. Here, K1, K2, and B are constants obtained by performing regression calculation processing by experiments in advance according to the shape of the oxygen sensor.

An example of the result of the calculation actually performed in accordance with steps 1 to 3 will be described. That is, the measurement and calculation in each of the above steps are represented by K1 = −4.
05, K2 = -0.42, B = 10.75, and simulated the state where the actual room temperature resistance values of the heaters of 3.64Ω and 2.77Ω were changed from -10 ° C to 575 ° C. The results shown in Table 1 below were obtained. From the results in Table 1, it can be seen that the method of the present invention can obtain a normal-temperature resistance value having almost no error from the actual normal-temperature resistance value.

[0012]

[Table 1]

[0013]

As is apparent from the above description, according to the present invention, the normal temperature resistance value of the heater used for controlling the temperature of the heater can be obtained by the predetermined calculation based on the above steps 1 to 3. Therefore, if the same PID control as that of the related art is performed based on the normal temperature resistance value, it is possible to perform suitable heater temperature control without troublesome actual measurement at the time of mounting and without input error. Become.
As a result, the measurement accuracy of the oxygen sensor can be kept high.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a specific example of implementing a temperature control method for an oxygen sensor according to the present invention.

FIG. 2 is a flowchart illustrating an example of a temperature control method for an oxygen sensor according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heater part 2 Temperature control device 11 Heater current measurement part 12 Heater voltage measurement part 13 Computing device 14 Power control PWM device 15 Heater power control device 16, 17 AC / DC converter 21 Room temperature resistance measurement switch 22 Power switch

Claims (1)

(57) [Claims] 1. An oxygen sensor comprising: a means for measuring a voltage applied to a heater portion of an oxygen sensor; a means for measuring a current flowing through the heater portion of the oxygen sensor; a heater power control device; In the method for controlling the temperature of the heater, when the power of the heater power control device is turned on, the following steps 1 to 3 are performed to obtain the normal temperature heater resistance RH0, and the applied voltage VH of the heater and the heater current IH
And the heater resistance RH = VH / IH is calculated, and the ratio RH / R between the heater resistance RH and the normal temperature heater resistance RH0 is calculated.
A method for controlling the temperature of an oxygen sensor, wherein the heater power is controlled so that the temperature of the oxygen sensor is constant, using H0 as a temperature signal of the sensor. Step 1: After applying the first applied voltage VH1 to the heater, the heater current IH1 is measured, and the heater resistance RH1 =
Calculate VH1 / IH1. Step 2: After applying the second applied voltage VH2 to the heater, the heater current IH2 is measured, and the heater resistance RH2 =
VH2 / IH2 is calculated, and the heater supply power PW2 = VH
Calculate 2 * IH2. Step 3: From the obtained RH1, RH2, and PW2, the normal-temperature heater resistance RH0 = K1 * RH1 / RH2 + K2 * P
Calculate W2 + B. (However, K1, K2, and B are constants previously determined based on the shape of the oxygen sensor.)