JPH05288713A - Supplying method of power for heater - Google Patents

Abstract

PURPOSE:To eliminate dependence on temperature and to prevent breakdown of an oxygen sensor immediately after a power source is turned ON, by supplying a heater with a power in an amount based on a relational formula between the temperature of an exhaust gas and the amount of the power supplied to the heater and by supplying the heater with a maximum impression voltage thereof through a limiter operating so that a maximum current may not be exceeded. CONSTITUTION:A temperature sensor 4 is provided at a position at which it is separated from a heater 3 provided integrally with an oxygen sensor and comes into contact with a gas to be measured, and measures the temperature of the gas regularly. Based on this temperature, a power control is executed by using a relational formula between the temperature of an exhaust gas determined beforehand and the amount of power supplied to the heater. The amount of the power supplied to the heater is used as a measured value and feedback control computation is executed inside a power operation signal converting part 8. When an operation signal resulting from the feedback control computation exceeds information on a fold-back current limiting characteristic in which the maximum value of a heater impression voltage and the maximum value of a heater current, a limiter circuit 7 determines a supply power control signal so that the signal may shift on the fold-back current limiting characteristic and controls a power operating part 2 so that this power be obtained. Accordingly, no breakdown of the oxygen sensor takes place.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for supplying electric power to a heater 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 or the exhaust gas of an incinerator,
An oxygen sensor with a heater that does not have a temperature detecting means is used. This oxygen sensor with a heater comprises an oxygen sensor capable of measuring the oxygen concentration by utilizing the ion conductivity of a solid electrolyte such as zirconia and a heater for heating the oxygen sensor. The electric power supplied to the heater of the oxygen sensor with a heater is generally supplied so that the electric power is always constant through a circuit having a constant resistance value by assembling a bridge.

[0003]

However, the oxygen sensor with a heater having no temperature detecting means and the temperature sensor for separately measuring the temperature of the gas to be measured, which are separately installed, are independent from each other, and this temperature sensor is used. Then, there was a problem that the feedback control of the oxygen sensor with a heater, which does not have the temperature detecting means, cannot be performed. Moreover, when the relationship between the actually supplied power and the output voltage of the oxygen sensor is examined, as shown in FIG. 5, the relationship between the supplied power and the output voltage of the oxygen sensor when the measured gas temperature changes. It was found that it became non-constant and changed depending on the temperature. As a result, there is a problem that the output voltage of the oxygen sensor changes depending on the temperature and the measurement accuracy deteriorates. Also,
Conventionally, no particular consideration was given to the power supply immediately after the power was turned on, and only a limiter was provided to control the maximum value of the current in order to prevent the destruction of the heater and the destruction of the oxygen sensor. However, in some cases, there is a problem that the heater is destroyed and the oxygen sensor is destroyed.

The object of the present invention is to solve the above problems,
An object of the present invention is to provide a power supply method for a heater, which eliminates temperature dependence and prevents destruction of the oxygen sensor immediately after the power is turned on.

[0005]

Power supply for the heater of the present invention
The power supply method supplies power to the heater of the oxygen sensor with heater.
In this method, (a) measure in advance with an exhaust gas temperature sensor.
Relational expression between fixed exhaust gas temperature tg and heater supply power SVPw
Then, using the obtained relational expression, based on the exhaust gas temperature tg,
Calculate the power supply amount SVPw and supply the calculated SVPw to the heater.
And / or (b) heater applied voltage Vh and heater
The characteristic of the heater current Ih is a fold-back characteristic,
Maximum applied voltage Vh_maxAbove and maximum heater current
Large current Ih _maxThe power is turned off via a limiter that does not exceed the above.
And a step of supplying the data to the data
Is. It should be noted that the fold-back characteristic in the present invention is a conventional one.
For example, see page 410 of the Linear IC Practical Circuit Manual, which is publicly known.
A property as described.

[0006]

In the above structure, the amount of electric power to be supplied is controlled based on the exhaust gas temperature by using the relational expression between the exhaust gas temperature and the electric power which is obtained in advance, so that even if the exhaust gas temperature changes, the amount of electric power always depends on the oxygen concentration. It is possible to obtain a constant output voltage. In addition, since the characteristics of the heater applied voltage Vh and the heater current Ih immediately after the power is turned on are fold-back characteristics, when the temperature of the oxygen sensor with a heater is low,
The voltage applied to the heater is Rh (Rh is the heater resistance of the oxygen sensor from the Ihl limiter current when the heater voltage of the Vh-Ih hang-down characteristic is 0 to the maximum limiter current Ih _max of the heater current). Then, the heater power supply device becomes an Ihl limiter current supply source, and the applied voltage of Vhl = Rh * Ihl. At this time, the power supplied to the heater is Pwl = Rh * Ihl * Ihl. Becomes This power heats the heater, increasing the heater resistance and
Ihl also becomes a little larger, the power supplied to the heater gradually increases, and the voltage applied to the heater also gradually increases to Ih _max , Vh
We will rise in the direction of _max . As a result, it is possible to achieve a method of supplying heater power by soft start, which eliminates damage to the heater and eventually damage to the sensor. Furthermore, the relationship between the heater supply power SVPw obtained from the exhaust gas temperature tg and the supply power Pwl at the startup when the power is turned on is Pw.
It is possible to smoothly shift to the temperature control by the heater supply power SVPw obtained from the exhaust gas temperature tg at the stage where l ≧ SVPw is replaced.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a specific example for carrying out the heater power supply method of the present invention. In FIG. 1, 1 is an AC / DC converter for converting 100 V AC, which is a commercial power source, into DC with a predetermined voltage, 2 is a power operation unit for controlling power, and 3 is an oxygen sensor (not shown) provided integrally. These heaters have the same structure as the conventional example. The feature of the present invention is that in the oxygen sensor with heater, the temperature sensor 4 is provided at a position in contact with the gas to be measured, which is separated from the oxygen sensor, and the temperature tg of the gas to be measured is constantly measured. On the basis of this, electric power control is performed by using a relational expression between the exhaust gas temperature tg and the heater supply electric power amount SVPw which is obtained in advance.

That is, the relational expression SVPw = A * tg ² + Btg + C between the exhaust gas temperature tg and the heater power amount obtained in advance, where A, B and C are experimental constants, and in the example of FIG. 4, A = -0.1769, B =- It was 0.00183 and C = 12.754.
Here, the electric power amount SVPw of the relational expression is set as the setting signal SV of the electric power operation signal conversion unit 8. On the other hand, the product PVPw = Vh * Ih of the heater applied voltage Vh and the heater current Ih, that is, the electric power PVPw supplied to the heater is used as the measured value, and the PID feedback control calculation is performed inside the electric power operation signal conversion unit 8.

Next, the operations of the setting circuit 5 and the limiter circuit 7 will be described. FIG. 2 is a graph showing an example of the operation of the Vh-Ih curve hanging characteristic of the setting circuit 5. With this configuration, it can be seen that an excessive voltage is not applied even when the power is constant and the current is small. Further, as shown in FIG. 3 which shows the elapsed time characteristics of Vh and Ih of the fold-back characteristic, neither Vh nor Ih have a significantly high value, and the durability of the heater can be increased. Further, when the operation signal of the above PID feedback control calculation result exceeds the fold-down characteristic information of the maximum value Vh _max of the heater applied voltage and the maximum value Ih _max of the heater current, the fold-down characteristic The power supply control signal is determined so as to move upward, and the power operation unit 2 is controlled so as to have this power.

The present invention is not limited to the above-described embodiments, but various modifications and changes can be made. For example, in the above-described embodiment, the power supply device provided with both the predetermined power control circuit based on the measured temperature and the limiter circuit based on the maximum voltage and the fold-back characteristic has been described. It is needless to say that each limiter circuit is provided individually, and it goes without saying that in the present invention, a power supply device that performs only the power control and a power supply device that includes only the limiter circuit are also within the range.

[0011]

As is apparent from the above description, according to the present invention, the predetermined power control circuit based on the measured temperature and / or the limiter circuit based on the maximum voltage and the fold-down characteristic are provided. Thus, it is possible to obtain a heater power supply method that has no temperature dependency and that does not cause the oxygen sensor to be destroyed immediately after the power is turned on.

[Brief description of drawings]

FIG. 1 is a block diagram showing a specific example for implementing a heater power supply method of the present invention.

FIG. 2 is a graph showing an example of the operation of the setting circuit 5 of the present invention.

FIG. 3 is a graph showing an example of elapsed time characteristics of the setting circuit 5 of the present invention.

FIG. 4 is a graph showing an example of the operation of the limiter circuit 7 of the present invention.

FIG. 5 is a graph showing the relationship between the supplied power and the output of the oxygen sensor.

[Explanation of symbols]

 1 AC / DC converter 2 Electric power operation part 3 Heater 4 Temperature sensor 5 Setting circuit 6 Measuring circuit 7 Limiter circuit 8 Electric power control operation signal conversion part

Claims (1)

[Claims] 1. A method for supplying electric power to a heater of an oxygen sensor with a heater, comprising: (a) obtaining a relational expression between an exhaust gas temperature tg previously measured by an exhaust gas temperature measuring element and a heater supply electric power amount SVPw, and obtaining the relation Using the formula to calculate the heater supply power SVPw based on the exhaust gas temperature tg and supply the calculated SVPw to the heater, and / or (b) The characteristics of the heater applied voltage Vh and the heater current Ih are fold-down characteristics. And a step of supplying electric power to the heater through a limiter that does not exceed the maximum applied voltage Vh _max of the heater applied voltage and the maximum current Ih _{max of the} heater current, and the oxygen sensor with a heater. Of heater power supply.