Heater

Abstract

A heater according to one aspect of the present disclosure comprises a heater body and a metal fitting. The heater body has a rod-shaped ceramic body and a heating resistor positioned inside the ceramic body. The metal fitting has a cylindrical metal substrate that extends from a first end toward a second end, and a first metal film that covers a first surface, which is the inner peripheral surface of the metal substrate. The heater body is joined to the metal fitting at a position including the first end via the first metal film. The first metal film has a higher thermal conductivity than the metal substrate. The metal fitting has, on the first surface, a first region that is closer to the second end than the heater body and that is not covered by the first metal film.

Description

Heater

[0001] This disclosure relates to a heater.

[0002] Conventionally, a heater has been known that includes a heater body having a heating resistor built into the tip side of a rod-shaped ceramic body, and a cylindrical metal fitting that holds the rear end side of the outer peripheral portion of the heater body.

[0003] Patent Document 1 describes providing a metal layer by Au (gold) plating on the inner peripheral surface of a cylindrical metal fitting related to the above heater.

[0004] Japanese Unexamined Patent Application Publication No. 2013-92353

[0005] The heater according to one aspect of the present disclosure includes a heater body and a fitting. The heater body has a rod-shaped ceramic body and a heating resistor located inside the ceramic body. The fitting has a cylindrical metal base extending from a first end to a second end, and a first metal film covering a first surface that is the inner peripheral surface of the metal base. The heater body is joined to the fitting at a position including the first end via the first metal film. The first metal film has a higher thermal conductivity than the metal base. The fitting has a first region on the first surface that is not covered by the first metal film closer to the second end than the heater body.

[0006] FIG. 1 is a cross-sectional view showing an example of the configuration of a heater according to the first embodiment. FIG. 2 is a cross-sectional view showing an example of the configuration of a heater according to the second embodiment. FIG. 3 is a cross-sectional view showing an example of the configuration of a heater according to the third embodiment. FIG. 4 is a cross-sectional view showing an example of the configuration of a heater according to the fourth embodiment.

[0007] Hereinafter, embodiments for implementing the heater according to the present disclosure (hereinafter referred to as "embodiments") will be described in detail with reference to the drawings. Note that the present disclosure is not limited by this embodiment. Also, the embodiments can be appropriately combined as long as the processing contents do not conflict. Also, in the following embodiments, the same parts are denoted by the same reference numerals, and duplicate explanations are omitted.

[0008] Furthermore, in the embodiments described below, expressions such as "constant," "orthogonal," "perpendicular," or "parallel" may be used, but these expressions do not require strict adherence to "constant," "orthogonal," "perpendicular," or "parallel" conditions. In other words, each of the above expressions allows for deviations, for example, in manufacturing accuracy or installation accuracy.

[0009] Conventionally, heaters are known that comprise a heater body with a heating resistor built into the tip of a rod-shaped ceramic body, and a cylindrical fitting that holds the rear end of the outer circumference of the heater body. Such heaters are widely used, for example, in oxygen sensors, air-fuel ratio sensors, glow plugs, and ignition heaters for oil fan heaters.

[0010] The cylindrical metal fittings in the heater described above are made of, for example, iron-based alloys, particularly SUS (Stainless Used Steel). However, SUS may deteriorate due to oxidation when heated for a long period of time. For this reason, in conventional technology, oxidation of the cylindrical metal fittings is prevented by providing a metal layer of Ni (nickel) plating or Au (gold) plating on the surface of the cylindrical metal fittings.

[0011] On the other hand, in recent years, there has been a demand for heaters with superior temperature characteristics compared to conventional heaters. Specifically, there is a need for higher maximum temperatures and shorter times to reach the maximum temperature. However, in the above heater, the thermal conductivity of the metal layer is higher than that of the cylindrical metal fitting. Therefore, when a metal layer is provided, the heat generated by the heating resistor tends to dissipate to the rear end of the heater through the metal layer. In such cases, the heating efficiency of the heater decreases, resulting in a lower maximum temperature and a longer time to reach the maximum temperature.

[0012] In contrast, the heater of this disclosure has a metal layer on the inner surface of the cylindrical metal fitting, extending from the first end to the second end, when the side of the cylindrical metal fitting closest to the heating resistor is designated as the first end and the opposite side as the second end, but there is no metal layer near the second end. Due to this configuration, the heater of this disclosure dissipates less heat from the rear end of the heater body.

[0013] <First Embodiment> First, the configuration of the heater according to the first embodiment will be described with reference to Figure 1. Figure 1 is a cross-sectional view showing an example of the configuration of the heater 100 according to the first embodiment.

[0014] The heater 100 of this disclosure may include a heater body 1 and a metal fitting 2. The heater body 1 may have a rod-shaped ceramic body 11 and a heating resistor 12 located inside the ceramic body 11.

[0015] Specifically, as shown in Figure 1, the heater body 1 may have a heating resistor 12 embedded inside the tip (the end on the negative X-axis side) of the ceramic body 11, and a lead portion 13 connected to the heating resistor 12.

[0016] The ceramic body 11 is, for example, silicon nitride (Si ３ N ４ It may be formed from a sintered body mainly composed of ) or aluminum nitride (AlN), aluminum oxide (Al ２ O ３ It may be formed from a sintered body mainly composed of alumina, silicon carbide (SiC), etc. The main component referred to here is, for example, a component that makes up more than 50% by mass of the material, and may be 80% by mass or more.

[0017] The heat-generating resistor 12 may be a conductor containing one or more metals selected from, for example, W, Ta, Nb, Ti, Mo, Zr, Hf, V, and Cr as a conductive component. It may also be a conductor containing silicides, carbides, and nitrides of the aforementioned elements. Furthermore, when the ceramic body 11 is a silicon nitride sintered body, Si ３ N ４ It may also be a conductor containing the above. Furthermore, the lead portion 13 may be a conductor mainly composed of tungsten, for example. Note that the thermal resistivity of the heating resistor 12 is higher than the thermal resistivity of the lead portion 13.

[0018] The lead portion 13 may have a lead portion 13a connected to one end of the heating resistor 12 and a lead portion 13b connected to the other end of the heating resistor 12. For example, by connecting the lead portion 13a to the positive electrode of an external electrode (not shown) and the lead portion 13b to the negative electrode of an external electrode (not shown), current can be passed through the heating resistor 12. This makes the heating resistor 12 generate heat.

[0019] The fitting 2 may have a metal substrate 21 which is a cylindrical metal member having a first end 211 and a second end 212, and extending from the first end 211 toward the second end 212. Such a metal substrate 21 may have a first surface 213 which is an inner circumferential surface and a second surface 214 which is an outer circumferential surface. The metal substrate 21 may be made of, for example, an iron-based alloy, particularly SUS. Specifically, the metal substrate 21 may be made of ferritic stainless steel. Examples of ferritic stainless steel include SUS430, 405, 409, and 434.

[0020] The metal substrate 21 may have a first metal film 22 covering a first surface 213 and a second metal film 23 covering a second surface 214. The first metal film 22 may be a plating film containing, for example, nickel, chromium, or the like.

[0021] The thickness of the first metal film 22 and the second metal film 23 may be, for example, 3 μm or more and 10 μm or less. The first metal film 22 and the second metal film 23 can be formed, for example, by an electrolytic plating method. The thermal conductivity of the first metal film 22 and the second metal film 23 is higher than the thermal conductivity of the metal substrate 21.

[0022] The heater body 1 may be joined to the metal substrate 21 via the first metal film 22 at its rear end. Specifically, the rear end of the ceramic body 11 (the end on the positive X-axis side) may be inserted into the cylindrical metal substrate 21 from the first end 211 side, and the rear end of the ceramic body 11 may be joined to the metal substrate 21 via the first metal film 22. Although not shown in Figure 1, the ceramic body 11 and the first metal film 22 may be bonded together with, for example, a soldering agent. Such a soldering agent preferably contains low electrical resistance components such as silver, gold, or copper.

[0023] The metal fitting 2 may have a first region 24 on the first surface 213 that is not covered by the first metal film 22, closer to the second end 212 than to the rear end of the ceramic body 11. The first region 24 may be, for example, an annular region. Also, the first region 24 may extend, for example, to the second end 212. In other words, the first region 24 may extend on the first surface 213 from the second end 212 toward the first end 211.

[0024] Such a first region 24 may be formed, for example, by forming a first metal film 22 on the entire first surface 213 of the metal fitting 2, and then dissolving and removing the first metal film 22 with an acidic liquid. The acidic liquid may be, for example, nitric acid. By using nitric acid, only the first metal film 22 can be dissolved without dissolving the metal substrate 21. Alternatively, the first region 24 may be formed by removing the first metal film 22 by blasting or polishing with abrasive paper. Furthermore, by masking the portion of the first surface 213 that will become the first region 24, and then forming the first metal film 22, it is possible to obtain a metal fitting 2 that has the first metal film 22 extending from the first end 211 toward the second end 212, while having a first region 24 near the second end 212 that does not have the first metal film 22.

[0025] As described above, the thermal conductivity of the first metal film 22 and the second metal film 23 is higher than that of the metal substrate 21. Therefore, heat generated in the heater body 1 is easily dissipated to the second end 212 side of the metal fitting 2 via the first metal film 22 and the second metal film 23. In particular, heat is easily dissipated to the second end 212 side of the metal fitting 2 via the first metal film 22 which is joined to the heater body 1. When heat is dissipated from the heater body 1 in this way, the heating efficiency of the heater body 1 decreases.

[0026] With the configuration in which the metal fitting 2 has a first region 24, the heat conduction path for heat dissipated to the second end 212 can be reduced. Therefore, the heat dissipation from the heater body 1 to the second end 212 can be reduced, and the decrease in the heating efficiency of the heater body 1 can be reduced. As a result, the maximum temperature of the heater body 1 can be increased. In addition, the time it takes for the heater body 1 to reach the maximum temperature can be shortened. Furthermore, the power required to maintain the maximum temperature can also be reduced.

[0027] The surface roughness of the first region 24, that is, the surface roughness of the metal substrate 21 exposed in the first region 24, may be greater than, for example, the surface roughness of the first metal film 22. Generally, the greater the surface roughness, the lower the heat conductivity. Therefore, when the surface roughness of the first region 24 is relatively large, the heat dissipation from the heater body 1 to the second end 212 can be more effectively reduced. Here, the surface roughness may be compared by observing the surfaces of the first region 24 and the first metal film 22 with a scanning electron microscope (SEM) at a magnification of, for example, 1000 to 5000 times. Alternatively, the surface roughness (Ra) may be measured and compared using a contact-type or non-contact-type surface roughness meter.

[0028] Furthermore, as shown in Figure 1, the metal fitting 2 may have a stepped portion 25 between the first metal film 22 and the first region 24. The stepped portion 25 is located at the end of the first metal film 22, which has thickness. The stepped portion 25 is formed by the difference in height between the first metal film 22 formed on the first surface 213 of the metal substrate 21 and the first region 24, which is a part of the first surface 213.

[0029] For example, when the fitting 2 is viewed in cross-section perpendicular to the direction from the first end 211 to the second end 212, the cross-sectional area of ​​the fitting 2 on the second end 212 side of the stepped portion 25 is smaller than the cross-sectional area of ​​the fitting 2 on the first end 211 side of the stepped portion 25. Generally, when heat is conducted from a region with a large cross-sectional area to a region with a small cross-sectional area of ​​the heat conduction path, the rate of heat conduction becomes the limiting factor, and the amount of heat conducted decreases. Therefore, with this configuration, the heat dissipation from the heater body 1 to the second end 212 via the fitting 2 can be reduced due to the rate-limiting effect.

[0030] <Second Embodiment> Next, the configuration of the heater 100 according to the second embodiment will be described with reference to Figure 2. Figure 2 is a cross-sectional view showing an example of the configuration of the heater 100 according to the second embodiment. As shown in Figure 2, the thickness of the stepped portion 25 of the metal fitting 2 according to the second embodiment may become thinner as it approaches the first region 24.

[0031] In such a case, for example, when the stepped portion 25 is viewed in cross-section perpendicular to the direction from the first end 211 to the second end 212, the cross-sectional area of ​​the stepped portion 25 decreases as it moves from the first end 211 side towards the first region 24 side. That is, when heat is conducted in the stepped portion 25 from the first end 211 side to the first region 24 side, the rate of heat conduction is limited, and the amount of heat conducted decreases. Therefore, with this configuration, the rate-limiting effect makes it possible to reduce the dissipation of heat from the heater body 1 to the second end 212 via the first metal film 22.

[0032] Furthermore, with this configuration, since the stepped portion 25 has a gentle curved surface, thermal stress concentration is less likely to occur in the stepped portion 25. This reduces the occurrence of cracks and other damage caused by thermal stress.

[0033] To adjust the thickness of the stepped portion 25, for example, when dissolving the first metal film 22 with an acidic liquid such as nitric acid, the contact time between the first metal film 22 and the acidic liquid can be adjusted. Specifically, for example, when dissolving and removing the first metal film 22 by immersing the rear end (the end on the positive X-axis side) of the metal fitting 2 in an acidic liquid such as nitric acid, the thickness of the stepped portion 25 can be adjusted by slowly immersing the metal fitting 2 to an arbitrary depth, maintaining it for an arbitrary time, and then gradually pulling it out. Alternatively, the stepped portion 25 may be polished to the desired shape by blasting or polishing with abrasive paper.

[0034] In Figure 2, an example is shown where the thickness of the metal substrate 21, specifically the thickness between the first surface 213 and the second surface 214, is the same along the direction from the first end 211 to the second end 212, that is, the metal substrate 21 has a cylindrical shape. However, the metal substrate 21 is not limited to this example; for example, the thickness of the metal substrate 21 on the second end 212 side of the stepped portion 25 may be smaller than the thickness on the first end 211 side of the stepped portion 25. In other words, the metal substrate 21 may also have a stepped portion.

[0035] With this configuration, the rate-limiting effect described above can be further enhanced, and thus the heat dissipation from the heater body 1 to the second end 212 via the metal fitting 2 can be more effectively reduced.

[0036] The thickness of the stepped portion 25, that is, the thickness of the first metal film 22, can be measured using, for example, a digital microscope.

[0037] <Third Embodiment> Next, the configuration of the heater 100 according to the third embodiment will be described with reference to Figure 3. Figure 3 is a cross-sectional view showing an example of the configuration of the heater 100 according to the third embodiment. As shown in Figure 3, the metal fitting 2 according to the third embodiment may have a second region 26 on the second surface 214 that is not covered by the second metal film 23, closer to the second end 212 than to the first end 211. That is, the heater 100 according to the third embodiment corresponds to a configuration in which the metal fitting 2 according to the first embodiment is provided with the second region 26.

[0038] As shown in Figure 3, the second region 26 may be, for example, an annular region. Also, the second region 26 may extend, for example, to the second end 212. In other words, the second region 26 may extend from the second end 212 toward the first end 211 on the second surface 214.

[0039] With the configuration in which the fitting 2 has a second region 26, the heat conduction path for heat dissipated from the heater body 1 to the second end 212 can be made smaller compared to the case in which the fitting 2 does not have a second region 26. Therefore, heat dissipation from the heater body 1 to the second end 212 can be more effectively reduced.

[0040] As shown in FIG. 3, when the length of the first metal film 22 along the direction from the second end 212 toward the first end 211 is L1 and the length of the first metal film 22 along the direction from the second end 212 toward the first end 211 is L2, L1 > L2 may hold. In other words, along the direction from the first end 211 toward the second end 212, the length of the first metal film 22 may be shorter than the length of the second metal film 23.

[0041] According to such a configuration, heat is less likely to be conducted from the first metal film 22 to the second metal film 23 through the metal base 21. Therefore, for example, heat dissipated from the surface of the second metal film 23 into the air can be reduced. Thereby, a decrease in the heating efficiency by the heater body 1 can be reduced.

[0042] As shown in FIG. 3, when the thickness between the first surface 213 and the second surface 214 of the metal base 21 is L3, L1 and L2 may be, for example, larger than L3.

[0043] <Fourth Embodiment> Next, the configuration of the heater 100 according to the fourth embodiment will be described with reference to FIG. 4. FIG. 4 is a cross-sectional view showing an example of the configuration of the heater 100 according to the fourth embodiment. As shown in FIG. 4, the fitting 2 according to the fourth embodiment may have an oxide film 27 in the first region 24. That is, the heater 100 according to the fourth embodiment corresponds to a configuration in which an oxide film 27 is provided on the fitting 2 according to the first embodiment.

[0044] The oxide film 27 can be formed, for example, by heating the fitting 2 having the first region 24 in a vacuum furnace. Specifically, when the metal base 21 exposed in the first region 24 is heated, an oxide film composed of an oxide of the metal contained in the metal base 21, for example, Cr ２ O ３ etc. is formed on the surface of the metal base 21.

[0045] The thermal conductivity of such an oxide film 27 is smaller than the thermal conductivity of the metal base 21. Therefore, according to the configuration having such an oxide film 27, heat dissipated from the first region 24 into the air can be reduced, for example, as compared with the case where the oxide film 27 is not provided. Thereby, a decrease in the heating efficiency by the heater body 1 can be reduced.

[0046] Furthermore, the surface roughness of the oxide film 27 may be greater than, for example, the surface roughness of the first metal film 22. Generally, the greater the surface roughness, the lower the heat conductivity. That is, a metal fitting 2 having an oxide film 27 with a relatively rough surface can more preferably reduce heat dissipation from the first region 24. Here, the surface roughness may be compared by observing the surfaces of the oxide film 27 and the first metal film 22 with an SEM at a magnification of, for example, 1000 to 5000 times. Alternatively, the surface roughness (Ra) may be measured and compared using a contact-type or non-contact-type surface roughness meter.

[0047] Although the present disclosure has been described in detail above, this disclosure is not limited to the embodiments described above, and various modifications and improvements are possible without departing from the gist of this disclosure.

[0048] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. Indeed, the embodiments described above can be embodied in a variety of forms. Furthermore, the embodiments described above may be omitted, replaced, or modified in various ways without departing from the scope and spirit of the appended claims.

[0049] Furthermore, this technology can also take the following configurations: (1) A heater comprising: a heater body having a rod-shaped ceramic body and a heating resistor located inside the ceramic body; and a fitting having a cylindrical metal substrate extending from a first end to a second end and a first metal film covering the inner circumferential surface of the metal substrate, wherein the heater body is joined to the fitting at a position including the first end via the first metal film, the first metal film has a higher thermal conductivity than the metal substrate, and the fitting has a first region on the first surface that is closer to the second end than the heater body and is not covered by the first metal film. (2) The heater according to (1), wherein the first region is annular. (3) The heater according to (1) or (2), wherein the first region extends to the second end. (4) The heater according to any one of (1) to (3), wherein the fitting has a stepped portion between the first metal film and the first region. (5) The heater according to (4), wherein the stepped portion becomes thinner as it approaches the first region. (6) The heater according to any one of (1) to (5), wherein the fitting has a second metal film covering the second surface which is the outer circumferential surface of the metal substrate, and on the second surface, there is a second region that is not covered by the second metal film and is closer to the second end than the heater body. (7) The heater according to (6), wherein the first region and the second region extend to the second end. (8) The heater according to (7), wherein the length of the first region in the axial direction of the metal substrate is longer than the length of the second region in the axial direction of the metal substrate. (9) The heater according to any one of (1) to (8), wherein the surface roughness of the first region is greater than the surface roughness of the first metal film. (10) The heater according to any one of (1) to (9), wherein the fitting has an oxide film in the first region. (11) The heater according to (10), wherein the surface roughness of the oxide film is greater than the surface roughness of the first metal film. (12) The heater according to any one of (1) to (11), wherein the metal substrate is ferritic stainless steel and the first metal film is nickel plating.

[0050] 1 Heater body 2 Metal fittings 11 Ceramic body 12 Heating resistor 13a, 13b Lead portion 21 Metal substrate 22 First metal film 23 Second metal film 24 First region 25 Step portion 26 Second region 27 Oxide film 100 Heater 211 First end 212 Second end 213 First surface 214 Second surface

Claims

1. A heater comprising: a heater body having a rod-shaped ceramic body and a heating resistor located inside the ceramic body; and a fitting having a cylindrical metal substrate extending from a first end to a second end and a first metal film covering the inner circumferential surface of the metal substrate, wherein the heater body is joined to the fitting at a position including the first end via the first metal film, the first metal film has a higher thermal conductivity than the metal substrate, and the fitting has a first region on its first surface that is closer to the second end than to the heater body and is not covered by the first metal film.

2. The heater according to claim 1, wherein the first region is annular.

3. The heater according to claim 1 or 2, wherein the first region extends to the second end.

4. The heater according to any one of claims 1 to 3, wherein the metal fitting has a stepped portion between the first metal film and the first region.

5. The heater according to claim 4, wherein the stepped portion becomes thinner as it approaches the first region.

6. The heater according to any one of claims 1 to 5, wherein the fitting has a second metal film covering a second surface which is the outer circumferential surface of the metal substrate, and the second surface has a second region that is not covered by the second metal film and is closer to the second end than the heater body.

7. The heater according to claim 6, wherein the first region and the second region extend to the second end.

8. The heater according to claim 7, wherein the length of the first region in the axial direction of the metal substrate is longer than the length of the second region in the axial direction of the metal substrate.

9. The heater according to any one of claims 1 to 8, wherein the surface roughness of the first region is greater than the surface roughness of the first metal film.

10. The heater according to any one of claims 1 to 9, wherein the metal fitting has an oxide film in the first region.

11. The heater according to claim 10, wherein the surface roughness of the oxide film is greater than the surface roughness of the first metal film.

12. The heater according to any one of claims 1 to 11, wherein the metal substrate is ferritic stainless steel and the first metal film is nickel plating.

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