JP2004253396A - Ceramic heater for sensor and oxygen sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic heater for a sensor, capable of heating a sensor quickly without generating problems such as a crack and disconnection, and to provide an oxygen sensor. <P>SOLUTION: A heating pattern 9 comprises a heating part 11 arranged in zigzag to make six columns at the edge of a substrate, and a lead part 12 extending from right and left end parts of the heating part 11 to the bottom side of the substrate. The line width of a center part 11a of the heating part 11 is set wider than the line width of right and left side area parts 11b1, 11b2, so that the resistance of the center part 11a of the heating part 11 is lower than the resistance of each side area part 11b1, 11b2. The line space of the center part 11a of the heating part 11 is set wider than the line space of the side area parts 11b1, 11b2, allowing the amount of heat generation of the center part 11a of the heating part 11 to be lower than the amount heat generation of either of the side area parts 11b1, 11b2. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a ceramic heater for a sensor used for, for example, an oxygen sensor of an internal combustion engine such as an automobile, and an oxygen sensor including the ceramic heater for the sensor.

  2. Description of the Related Art Conventionally, a laminated plate heater (hereinafter simply referred to as a ceramic heater) including a ceramic substrate and a conductive resistor made of Pt or W as a heating pattern has been widely used for an oxygen sensor or a general-purpose heater. I have.

  For example, as shown in FIG. 5A, a plate-shaped oxygen sensor element P2 using a metal oxide sensitive body such as titania as the gas-sensitive element P1 is formed integrally with the oxygen sensor element P2 by lamination. The ceramic heater P3 is used. As the ceramic heater P3, for example, as shown in FIG. 5B, a heating pattern P6 including a meandering heating portion P4 and a pair of lead portions P5 extending from the heating portion P4 is formed on a ceramic substrate P7. Things are known.

However, this ceramic heater P3 has the following problems (1) and (2), and it has been desired to solve the problems.
(1) That is, when the temperature is increased by applying an applied voltage to the ceramic heater P3 used for the oxygen sensor element P2, for example, at the time of starting the internal combustion engine, the temperature is increased during the temperature increase. An excessive temperature difference occurs between the central portion (where the heat generating portions P4 are concentrated) of the ceramic substrate P7 and the side portions (in the width direction where heat can easily escape). As a result, due to the difference in thermal expansion between the central portion and the side portions of the heat generating portion P4, cracks P8 occur in the ceramic substrate P7 and the heat generating portion P4 is disconnected.

  (2) In recent years, it has been obligated in recent years to detect deterioration of oxygen sensors, catalyst devices, control sensors, and the like in OBD-II (On board diagnosis) in the emission regulations of automobiles in the United States. Has also occurred.

  The OBD-II is a regulation by the environmental protection law in California, USA, which is expected to be enforced from around 1996. When the engine emission does not meet the regulation value, the regulation value is not satisfied. It is obligatory to display this so that the driver can understand it. If a failure occurs in this display system, it is only possible to recall the failure, so it is necessary to detect the deterioration of the oxygen sensor, the catalyst device, the control sensor, etc. It is very important that it works. For this reason, it is necessary to mount a diagnostic oxygen sensor downstream of the catalyst device, but in such a case, the following problems may occur.

  That is, when the condensed water accumulated in the catalyst device at the time of starting the engine is scattered in a granular form and adheres to the gas-sensitive element P1 heated by the heater on the downstream side of the catalyst device, the gas-sensitive element P1 may be destroyed. is there. For this reason, when the engine is started, it is necessary to turn on the heater 30 seconds after the start of the engine, when the scattering of condensed water is sharply reduced, without heating the heater, and to raise the temperature to a temperature at which the gas-sensitive element P1 is activated. As a result, the air-fuel ratio is not accurately controlled until the temperature reaches the temperature at which the gas-sensitive element P1 is activated, so that the purification rate of the exhaust gas deteriorates and the fuel efficiency deteriorates.

  Therefore, it is necessary to raise the temperature to a temperature at which the gas-sensitive element P1 is activated in as short a time as possible. In particular, a normal air-fuel ratio control sensor mounted upstream of the catalyst device is activated about 50 seconds after the engine is started. Since the temperature reaches the activation temperature, it is desired that the diagnostic oxygen sensor be activated within this time, that is, within 20 seconds after the start of energization.

  As a countermeasure, it is conceivable that the ceramic heater P3 (as shown in FIG. 5) used for the oxygen sensor element P2 is quickly heated by applying an applied voltage higher than the conventional applied voltage. In this case, a sudden temperature change causes a larger temperature difference between the central portion and the side portion of the ceramic substrate P7 described above. In other words, when the temperature is raised quickly, there is a major problem that cracks P8 and disconnections become more remarkable than in the past.

  The present invention has been made to solve the above problems, and has as its object to provide a ceramic heater for a sensor and an oxygen sensor that can quickly heat the sensor without causing a problem such as a crack or disconnection. And

The invention of claim 1 for achieving the above object is as follows.
In a ceramic heater for a sensor in which a heating pattern formed of a heating portion turned in a longitudinal direction of the ceramic base and a lead portion extending from the heating portion is formed on a ceramic base, the amount of heat generated at a central portion of the heating portion is determined by a side edge. The present invention provides a ceramic heater for a sensor, wherein the ceramic heater is set to be smaller than the calorific value of the portion.

The invention of claim 2 is
2. The meandering part is formed by meandering the heat generating part, and a line width of a central part of the meandering part is set to be larger than a line width of a side part of the meandering part. The gist is a ceramic heater for a sensor.

The invention of claim 3 is
The meandering portion is formed by meandering the heat generating portion, and a line interval at a center portion of the meandering portion is set wider than a line interval at a side portion of the meandering portion. The gist is the ceramic heater for sensor described.

The invention of claim 4 is
3. The sensor ceramic heater according to claim 1, wherein a resistance value of the central portion of the heat generating portion is set in a range of 20 to 80% of a resistance value of the side portion. .

The invention of claim 5 is
The gist of the sensor ceramic heater according to claim 4, wherein a resistance value of the central portion of the heat generating portion is set in a range of 30 to 70% of a resistance value of the side portion.

The invention of claim 6 is
A sensor comprising: a ceramic heater for a sensor according to any one of claims 1 to 5; a gas-sensitive element whose resistance value changes with respect to oxygen concentration; and an output extraction unit for extracting an output from the gas-sensitive element provided on a ceramic base. And an oxygen sensor element with a heater formed by laminating the oxygen sensor element and a heater, and the oxygen sensor element with the heater is housed in a metal case.

The invention of claim 7 is
7. The gist of the oxygen sensor according to claim 6, wherein the heat generating portion and the gas-sensitive element are respectively formed on front and back surfaces of the ceramic base at corresponding positions.

  Here, an alumina substrate can be used as the ceramic substrate, Pt and W can be used as the heat generation pattern, and titania can be used as the gas-sensitive element.

  In the ceramic heater for a sensor according to the first aspect, the calorific value of the central portion of the heat generating portion formed on the ceramic base is set smaller than that of the side portion. Therefore, even if heat escapes from the side portion and the temperature decreases, the calorific value of the central portion is small, so that the temperature difference between the side portion and the central portion is small. Therefore, even if the heating is performed rapidly, the temperature difference is not so large, so that the occurrence of cracks and disconnection can be prevented not only in a normal use condition but also during the rapid heating.

  In the ceramic heater for a sensor according to the second aspect, the line width at the central portion of the meandering portion of the heat generating portion is set to be larger than the side portion. Therefore, even when the same voltage is applied, the calorific value of the central portion is reduced, so that the temperature difference between the side portion and the central portion is reduced, and the crack is generated not only in the normal use condition but also in the rapid heating. Or disconnection can be prevented.

  In the ceramic heater for a sensor according to the third aspect, the line interval in the central portion of the meandering portion of the heat generating portion is set wider than the side portion. Therefore, since the ratio of the heat generation pattern in the center portion is small, the heat generation amount in the center portion is small, the temperature difference between the center portion and the side portion is small, and not only in the normal use state, but also in the case of rapid heating. Also, the occurrence of cracks and disconnections can be prevented.

  In the sensor ceramic heater according to the fourth aspect, the resistance value at the central portion of the heat generating portion is set to be 20 to 80% of the resistance value at the side portion, and the central portion is set so that the calorific value is smaller. The temperature difference between the peripheral portion and the side portion is reduced, so that cracks and disconnections can be prevented not only during normal use but also during rapid heating.

  In the ceramic heater for a sensor according to the fifth aspect, since the resistance value of the central portion of the heat generating portion is set to 30 to 70% of the resistance value of the side portion, the temperature difference between the central portion and the side portion is further reduced. As a result, cracks and disconnections can be more suitably prevented not only during normal use but also during rapid heating.

  In the oxygen sensor according to the sixth aspect, the oxygen sensor element with the heater, in which the ceramic heater for the sensor according to the first to fifth aspects and the detection unit are stacked, is housed in a metal case and used. In addition, the gas-sensitive element can be heated quickly without causing cracks and disconnections even during rapid heating, so that measurement by the sensor can be started quickly.

  In the oxygen sensor according to claim 7, since the heat-generating portion and the gas-sensitive element are respectively formed on the corresponding front and back surfaces of the ceramic base, the heat-generating portion is arranged at a position most suitable for heating the gas-sensitive element. There is an advantage that heating can be performed efficiently and measurement by a sensor can be started quickly.

  In the ceramic heater for a sensor according to the first aspect, the calorific value of the central portion of the heat generating portion formed on the ceramic base is set smaller than that of the side portion. Therefore, even if heat escapes from the side portion and the temperature decreases, the calorific value of the central portion is small, so that the temperature difference between the side portion and the central portion is small. Therefore, not only in the case of normal heating but also in the case of rapid heating, since the temperature difference is not so large, the occurrence of cracks and disconnection during normal heating and rapid heating are prevented.

  In the ceramic heater for a sensor according to the second aspect, the line width at the central portion of the meandering portion of the heat generating portion is set to be larger than the side portion. Therefore, even when the same voltage is applied, the calorific value of the central portion is reduced, so that the temperature difference between the side portion and the central portion is reduced and the occurrence of cracks and disconnections is prevented as in the case of the first aspect. Is done.

  In the ceramic heater for a sensor according to the third aspect, the line interval in the central portion of the meandering portion of the heat generating portion is set wider than the side portion. Therefore, since the ratio of the heat generation pattern in the central portion is small, the amount of heat generated in the central portion is reduced, and the temperature difference between the central portion and the side portion is reduced, as in the case of claim 1, and cracks and disconnections are caused. The occurrence is prevented.

  In the ceramic heater for a sensor according to the fourth aspect, the resistance value of the central portion of the heat generating portion is set to be 20 to 80% of the resistance value of the side portion, that is, the calorific value is smaller in the central portion. As a result, the temperature difference between the peripheral portion and the side portion is reduced, thereby preventing the occurrence of cracks and disconnections.

  In the ceramic heater for a sensor according to the fifth aspect, the resistance value of the central portion of the heat generating portion is set to be 30 to 70% of the resistance value of the side portion, so that the temperature difference between the central portion and the side portion. Is further reduced, and the occurrence of cracks and disconnections is prevented.

  In the oxygen sensor according to the sixth aspect, the sensor ceramic heater according to any one of the first to fifth aspects and the detection unit are stacked to form an oxygen sensor element with a heater, and the oxygen sensor element with a heater is a metal case. The gas-sensitive element can be quickly heated without causing cracks or disconnections.

  In the oxygen sensor according to claim 7, since the heat-generating portion and the gas-sensitive element are respectively formed on the corresponding front and back surfaces of the ceramic base, the heat-generating portion is arranged at a position most suitable for heating the gas-sensitive element. Heating can be performed efficiently.

Hereinafter, a ceramic heater for a sensor and an oxygen sensor according to an embodiment of the present invention will be described.
(Example 1)
As shown in FIG. 1, a ceramic heater 1 for a sensor according to the present embodiment is used for heating a gas-sensitive element 5, and the plate-shaped ceramic heater 1 is laminated on a plate-shaped detection unit 2. Thus, a columnar oxygen sensor element 3 having a width of 4 mm, a length of 40 mm and a thickness of 2.2 mm is formed.

  That is, the detection unit 2 is composed of a gas-sensitive element 5 made of a metal oxide sensitive body such as titania and a Pt in contact with the gas-sensitive element 5 on a first alumina substrate (sensor substrate) 4 having a thickness of 1 mm. A pair of detection electrodes 6 and an insulating sheet 7 made of alumina and having a thickness of 0.2 mm which covers most of the detection electrodes 6 are provided. The electrode area in contact with the electrode for use 6 is defined, and the portion other than the contact between the gas-sensitive element 5 and the detection electrode 6 is sealed from the atmosphere. On the other hand, the ceramic heater 1 has a heat generating pattern 9 made of Pt provided on a second alumina substrate 8 having a thickness of 1 mm. The oxygen sensor element 3 is configured by being stacked. Therefore, in the present embodiment, the heat generating pattern 9 is sandwiched between the first alumina substrate 4 and the second alumina substrate 8, and the heat generating portion 11 of the heat generating pattern 9 and the gas-sensitive element 5 are connected to the first alumina substrate 4. That is, they are arranged at the same position on the front and back surfaces with the substrate 4 interposed therebetween.

  As shown in FIG. 2, the heat generating pattern 9 provided on the second alumina substrate 8 includes a heat generating portion 11 meandering in six rows at the front end side of the substrate, and a heat generating portion 9 extending from the left and right ends of the heat generating portion 11. And a pair of lead portions 12 extending to the root side.

In particular, the present embodiment, the line width of the central portion 11a of the heating portion 11 (e.g., 0.35 mm) is thicker be set from the left and right side portions 11b _1, 11b ₂ of the line width (e.g., 0.3 mm) Accordingly, the resistance value of the central portion 11a of the heating portion 11 is set so as be smaller than the resistance value of each side portion 11b _1, 11b _2. The line spacing of the central portion 11a of the heating portion 11 (e.g., 0.40 mm) is set wider than side portions 11b _1, 11b ₂ of the line spacing (for example, 0.33 mm).

Thus, the heating value of the central portion 11a of the heating portion 11 is set so as be smaller than any of the calorific value of the side portions 11b _1, 11b ₂ of the right and left. The line width and line interval of the heat generating portion 11 may be set so as to increase in order toward the center of the alumina substrate 8.

As shown in FIG. 3, the oxygen sensor element 3 having the above-described ceramic heater 1 is provided with a metallic sleeve 23 and a gas-sensitive element 5 through a ceramic sleeve 21 and a glass seal 22. It is stored in a metal case 25 made up of a metal cap 24 and the like, and is used, for example, for detecting the oxygen concentration of an internal combustion engine.
<Experimental example 1>
Next, an experimental example performed for confirming the effect of the ceramic heater of the present embodiment will be described.

  In this experimental example, the ceramic heater portion having the structure of the first embodiment was used. That is, a sample of a ceramic heater (4.0 mm in width × 40.0 mm in length × 2.0 mm in thickness) in which a heating pattern was sandwiched between the first alumina substrate and the second alumina substrate was prepared. .

  More specifically, as ceramic heaters, as shown in Table 1 below, 25 samples (Nos. 1 to 3) having different line widths, resistance values, and line intervals at the central portion and side portions of the heating portion were each used. Manufactured. Similarly, 25 comparative examples (No. 4) in which the line width and the line interval were not changed were manufactured.

  In this experimental example, as shown in FIG. 2, the side piece is a meandering part of one reciprocation of the left and right side pieces, and the center of the heat generating part is a part excluding the side piece. Further, the resistance values in Table 1 indicate an average value of 25 pieces.

  Then, tests were performed on the ceramic heater samples under the following test conditions 1) and 2). The results are shown in Table 2 below.

  1) Set the heater resistance (total resistance) to about 5.9Ω. This is a resistance value at which the applied voltage is DC 11 V and the amount of power required for the gas sensing element to reach 500 ° C. 20 seconds after the voltage is applied.

  2) As a test condition, after applying a voltage of 14.5 V DC for 20 seconds, it was examined whether or not cracks occurred in the heater.

As is evident from Table 2, the device according to the present example has a small crack generation rate even when a predetermined applied voltage is applied, and the comparative example has a large crack generation rate, which is not preferable. .
<Experimental example 2>
Next, an experimental example will be described in which the state of occurrence of cracks in the ceramic heater of the present embodiment was examined in detail.

  In the present experimental example, in the ceramic heater having the structure used in Experimental Example 1, 25 samples were prepared in which the ratio between the resistance value at the center and the resistance value on one side was changed by 10%. Then, the crack generation rate was examined under the experimental conditions of the above 2) (DC 14.5 × applied for 20 seconds). The result is shown in FIG.

  As is clear from FIG. 4, when the ratio of the resistance value at the central portion to the resistance value at one side (the resistance value at the central portion / the resistance value at one side at one side) is 30 to 70%, the crack generation rate Is extremely small, almost zero, which is extremely suitable.

  It should be noted that the present invention is not limited to the above-described embodiment at all, and it goes without saying that the present invention can be implemented in various modes without departing from the gist of the present invention.

FIG. 2 is an exploded perspective view illustrating the oxygen sensor element according to the embodiment. It is a partially broken plan view showing the ceramic heater of the present example. It is sectional drawing which shows the oxygen sensor of a present Example. 9 is a graph showing a crack generation rate in Experimental Example 2. It is explanatory drawing which shows a prior art.

Explanation of reference numerals

1 ... ceramic heater, 2 ... detector,
3 oxygen sensor element 4 first alumina substrate
5 ... gas sensitive element, 8 ... second alumina substrate,
9: heat generation pattern, 11: heat generation section,
12 Lead part

Claims (7)

A ceramic heater for a sensor in which a heating pattern formed of a heating portion turned in a longitudinal direction of the ceramic base and a lead portion extending from the heating portion is formed on the ceramic base,
A ceramic heater for a sensor, wherein a calorific value of a central portion of the heat generating portion is set smaller than a calorific value of a side portion. 2. The method according to claim 1, wherein the heat generating portion is meandered to form a meandering portion, and a line width at a central portion of the meandering portion is set to be larger than a line width at a side portion of the meandering portion. Ceramic heater for sensors. The meandering portion is formed by meandering the heat generating portion, and a line interval at a center portion of the meandering portion is set wider than a line interval at a side portion of the meandering portion. The ceramic heater for a sensor as described in the above. 3. The sensor ceramic heater according to claim 1, wherein a resistance value of the central portion of the heat generating portion is set in a range of 20% to 80% of a resistance value of the side portion. 5. The sensor ceramic heater according to claim 4, wherein a resistance value of the central portion of the heat generating portion is set in a range of 30 to 70% of a resistance value of the side portion. A sensor comprising: a ceramic heater for a sensor according to any one of claims 1 to 5; a gas-sensitive element whose resistance value changes with respect to oxygen concentration; and an output extraction unit for extracting an output from the gas-sensitive element provided on a ceramic base. And an oxygen sensor element with a heater formed by laminating the oxygen sensor element with the heater and the oxygen sensor element with the heater housed in a metal case. 7. The oxygen sensor according to claim 6, wherein the heat generating portion and the gas-sensitive element are respectively formed on front and back surfaces of the ceramic base at corresponding positions.

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