JP3197603B2 - Heater power supply 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 supplying 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 and the oxygen concentration in exhaust gas of an incinerator,
An oxygen sensor with a heater having no temperature detecting means 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 electric power supplied to the heater of this oxygen sensor with a heater is generally supplied at a constant power through a circuit having a bridge and a constant resistance value.

[0003]

However, an oxygen sensor with a heater having no temperature detecting means and a separately installed temperature sensor for measuring the temperature of the gas to be measured are independent of each other. Thus, there has been a problem that feedback control of an oxygen sensor with a heater having no temperature detecting means cannot be performed. When the relationship between the actually supplied power and the output voltage of the oxygen sensor is examined, as shown in FIG. 5, when the measured gas temperature changes, the relationship between the supplied power and the output voltage of the oxygen sensor becomes It was found that it was not constant and changed depending on the temperature. As a result, there has been a problem that the output voltage of the oxygen sensor changes depending on the temperature, and the measurement accuracy deteriorates. Also,
In the past, no special consideration was given to the power supply immediately after the power was turned on, and only a limiter was provided to regulate the maximum value of the current to prevent destruction of the heater and, consequently, destruction of the oxygen sensor. In some cases, there has been a problem that the heater may be destroyed and the oxygen sensor may be destroyed.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a heater power supply method capable of eliminating temperature dependence and eliminating destruction of an oxygen sensor immediately after turning on a power supply.

[0005]

According to the present invention, there is provided a method for supplying electric power to a heater, comprising the steps of: (a) exhaust gas temperature tg measured in advance by an exhaust gas temperature measuring element; A relational expression with the supplied electric energy SVPw: SVPw = A * tg ² + B * tg + C (A, B, and C are constants)
A step of obtaining the heater supply electric energy SVPw based on the exhaust gas temperature tg using the obtained relational expression and supplying the obtained SVPw to the heater, and / or (b) the heater applied voltage Vh and the heater current
Characteristics of the Ih has a shaped drooping characteristics of full, the maximum current I of maximum applied voltage Vh _max or more and heater current of the voltage applied to the heater
supplying electric power to the heater through a limiter that does not exceed h _max .
It should be noted that the letter-shaped characteristic in the present invention means a characteristic as described in, for example, page 410 of a linear IC practical circuit manual which is conventionally known.

[0006]

In the above-described configuration, by controlling the amount of electric power to be supplied based on the exhaust gas temperature using the relational expression between the exhaust gas temperature and the electric energy obtained in advance, the amount of electric power is always adjusted according to the oxygen concentration even if the exhaust gas temperature changes. A constant output voltage can be obtained. In addition, since the characteristics of the heater applied voltage Vh and the heater current Ih immediately after the power is turned on are set to the fold-down characteristics, when the temperature of the oxygen sensor with the heater is low,
The voltage applied to the heater changes the heater resistance of the oxygen sensor from Rh (Rh) to the maximum heater current (Ih _max) from the Ihl limiter current when the heater voltage of the Vh-Ih character drooping characteristic is 0 to Rh (Rh is Then, the heater power supply device becomes an Ihl limiter current supply source and has an applied voltage of Vhl = Rh * Ihl. At this time, the power supply to the heater is Pwl = Rh * Ihl * Ihl Becomes This power heats the heater, increasing the heater resistance and
Ihl also increases slightly, the heater supply power gradually increases, and the heater applied voltage also gradually increases, and Ih _max and Vh
_{It rises in} the direction of _max . As a result, it is possible to achieve a heater power supply method with a soft start, in which damage to the heater and thus damage to the sensor are eliminated. Further, the relationship between the heater supply power SVPw obtained from the exhaust gas temperature tg and the supply power Pwl at the start-up when the power is turned on is represented by Pw
At the stage where l ≧ SVPw, the control can be smoothly shifted to the temperature control based on the heater supply power SVPw obtained from the exhaust gas temperature tg.

[0007]

FIG. 1 is a block diagram showing a specific example for implementing a method for supplying power to a heater according to the present invention. In FIG. 1, reference numeral 1 denotes an AC / DC converter for converting an AC 100 V, which is a commercial power supply, into DC of a predetermined voltage; 2, an electric power operation unit for controlling electric power; and 3, an oxygen sensor (not shown) integrally provided. And these configurations are not different from the conventional example. A feature of the present invention is that in the oxygen sensor with a 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. The point is that the power control is performed by using a relational expression between the exhaust gas temperature tg and the heater supply 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 obtained in advance, where A, B and C are experimental constants, and A = −0.1769 and B = − in the example of FIG. 0.00183, C = 12.754.
Here, the electric energy SVPw of the relational expression is set as the setting signal SV of the electric power operation signal converter 8. On the other hand, a PID feedback control operation is performed inside the power operation signal converter 8 using the product PVPw of the heater applied voltage Vh and the heater current Ih as a measured value, that is, the amount of power PVPw supplied to the heater.

Next, the operation 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-shaped drooping characteristic of the setting circuit 5. With such a configuration, it can be seen that an excessive voltage is not applied even when the power is constant and the current is small. In addition, as shown in FIG. 3, the elapsed time characteristics of Vh and Ih of the V-shaped drooping characteristics, Vh and Ih do not become prominently high values, and the durability of the heater can be increased. Further, when the operation signal of the PID feedback control calculation result exceeds the vertical droop characteristic information having the upper limit of the maximum value Vh _max of the heater applied voltage and the maximum value Ih _max of the heater current, the vertical droop characteristic The supply power control signal is determined so as to move upward, and the power operation unit 2 is controlled so as to obtain this power.

[0010] The present invention is not limited to the above-described embodiment, but can be variously modified and changed. 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 V-shaped drooping characteristic has been described. It is significant that the limiter circuits are provided independently, respectively, and it goes without saying that a power supply device that performs only the power control and a power supply device that includes only the limiter circuit in the present invention are also within the range.

[0011]

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

[Brief description of the drawings]

FIG. 1 is a block diagram showing a specific example of implementing a heater power supply method according to 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 an elapsed time characteristic 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 a relationship between supply power and an output of an oxygen sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC / DC converter 2 Power operation part 3 Heater 4 Temperature sensor 5 Setting circuit 6 Measurement circuit 7 Limiter circuit 8 Power control operation signal conversion part

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/409 G01N 27/04

Claims (1)

(57) [Claims] 1. A method for supplying electric power to a heater of an oxygen sensor with a heater, comprising: (a) a relational expression between an exhaust gas temperature tg previously measured by an exhaust gas temperature measuring element and a heater supply electric energy SVPw : SVPw = A * tg ² + B * tg + C (A, B and C are constants)
A step of obtaining the heater supply electric energy SVPw based on the exhaust gas temperature tg using the obtained relational expression and supplying the obtained SVPw to the heater, and / or (b) the heater applied voltage Vh and the heater current
Characteristics of the Ih has a shaped drooping characteristics of full, the maximum current I of maximum applied voltage Vh _max or more and heater current of the voltage applied to the heater
h feeding _max power through a limiter that do not above the heater, the heater method of power supply of the heater with the oxygen sensor, comprising the city.