Ceramic heaters, ceramic heater modules, liquid heating devices, and methods for manufacturing ceramic heaters.

Abstract

The present invention provides a ceramic heater, a ceramic heater module, a liquid heating device, and a method for manufacturing a ceramic heater, thereby improving the thermal efficiency of the ceramic heater. The ceramic heater (20) comprises: a ceramic body (51) which is cylindrical, having a first opening at one end through which a medium can flow in, and a second opening at the other end through which a medium can flow out; and a first resistive heating element (62) disposed on at least a portion of the inner circumferential surface of the ceramic body (51), which heats up by energizing.

Description

Technical Field

[0001] This disclosure relates to ceramic heaters, ceramic heater modules, liquid heating devices, and methods for manufacturing ceramic heaters. Background Technology

[0002] Previously, ceramic heaters have been known as heaters for controlling the heating of a medium (for example, see Patent Document 1).

[0003] The ceramic heater has a cylindrical ceramic substrate with an embedded resistance heating element, and the medium is configured to flow across the surfaces (inner and outer circumferential surfaces) of the ceramic substrate. Heat generated by the resistance heating element through the application of electricity is conducted within the ceramic substrate and exchanges heat with the medium flowing on its surface. Thus, the medium is heated.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2017-4915 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] In conventional ceramic heaters, the resistance heating element is embedded in the radially outer part of the ceramic substrate. Due to this structure, heat generated by the resistance heating element is more easily transferred to the outer surface of the ceramic substrate compared to the inner surface. Therefore, the medium is more easily heated when flowing on the outer surface compared to the period flowing on the inner surface of the ceramic substrate. Such ceramic heaters offer potential for improvement in thermal efficiency.

[0009] This invention was made to address the aforementioned problems. Specifically, one objective of this invention is to provide a technique that can improve the thermal efficiency of ceramic heaters.

[0010] Solution for solving the problem

[0011] The ceramic heater (20) of the present invention comprises: a ceramic body (51) which is cylindrical, having a first opening (O1) at one end through which a medium can flow in, and a second opening (O2) at the other end through which the medium can flow out; and a first resistive heating element (62) disposed on at least a portion of the inner circumferential surface of the ceramic body, which heats up by passing an electric current through it.

[0012] The effects of the invention

[0013] In the ceramic heater of the present invention, a first resistive heating element is provided on the inner peripheral surface of the ceramic body. According to this structure, the heat generated by the first resistive heating element is more easily transferred to the inner peripheral surface of the ceramic body compared to the outer peripheral surface. Therefore, from the viewpoint of the temperature rise of the medium caused by the first resistive heating element, the medium is more easily heated during its flow on the inner peripheral surface compared to the period during which it flows on the outer peripheral surface of the ceramic body. Here, generally in a cylindrical heating element, the thermal efficiency of heating the medium flowing on the inner peripheral surface of the heating element is higher than the thermal efficiency of heating the medium flowing on the outer peripheral surface of the heating element. Therefore, the ceramic heater according to the present invention can improve thermal efficiency compared to a structure in which the first resistive heating element is provided on the outer peripheral surface of the ceramic body.

[0014] In one aspect of the invention, the ceramic heater (20) further comprises a first ceramic layer (52) covering the surface of the first resistive heating element (62).

[0015] According to this structure, since the surface of the first resistive heating element is covered by the first ceramic layer, the durability of the first resistive heating element can be improved.

[0016] In one aspect of the invention, the ceramic heater (20) further comprises a second resistive heating element (63) disposed on at least a portion of the outer peripheral surface of the ceramic body (51) and heated by energizing.

[0017] In this ceramic heater, a second resistance heating element is also provided on the outer peripheral surface of the ceramic body. According to this structure, by appropriately setting the connection method between the first and second resistance heating elements, not only can the thermal efficiency be improved, but the possibility of boiling in a liquid medium can also be significantly reduced. Here, the connection method typically refers to a parallel connection. To illustrate the effect of the parallel connection, as a conventional example, a ceramic heater with a third resistance heating element provided only on the outer peripheral surface of the ceramic body is shown. If the resistance value of the third resistance heating element is made consistent with the combined resistance value of the first and second resistance heating elements, and the same voltage is applied to both ceramic heaters, the electricity generated in both ceramic heaters is the same, and the electricity in each of the first and second resistance heating elements is lower than the electricity in the third resistance heating element (for example, if the resistance values ​​of the first and second resistance heating elements are each set to 2R, and the resistance value of the third resistance heating element is set to R, then the electricity in each of the first and second resistance heating elements is half the electricity in the third resistance heating element). According to this structure, in conventional ceramic heaters, the medium is barely heated during its flow on the inner circumferential surface of the ceramic body, but is rapidly heated by the heat from a third resistive heating element during its flow on the outer circumferential surface. In contrast, in a ceramic heater of one aspect of the present invention, the medium is slowly heated primarily by the heat from a first resistive heating element during its flow on the inner circumferential surface of the ceramic body, and slowly heated primarily by the heat from a second resistive heating element during its flow on the outer circumferential surface of the ceramic body. That is, in one aspect of the present invention, the power density (energy density per unit time) of the ceramic body can be reduced compared to conventional examples. Therefore, the rapid heating of the liquid medium is less likely to occur, significantly reducing the possibility of boiling of the liquid medium, and consequently suppressing the occurrence of cracks in the ceramic heater caused by boiling.

[0018] In one aspect of the invention, the ceramic heater (20) further comprises a second ceramic layer (53) covering the surface of the second resistive heating element (63).

[0019] According to this structure, since the surface of the second resistive heating element is covered by a second ceramic layer, the durability of the second resistive heating element can be improved.

[0020] In one aspect of the invention, the radial thickness of the first ceramic layer (52) is 0.1 mm or more and 1.0 mm or less.

[0021] By making the radial thickness of the first ceramic layer 0.1 mm or more, the strength of the first ceramic layer can be ensured. In addition, by making the radial thickness of the first ceramic layer 1.0 mm or less, the thermal conductivity generated by the first resistive heating element can be appropriately maintained.

[0022] In one aspect of the invention, the radial thickness of the second ceramic layer (53) is 0.1 mm or more and 1.0 mm or less.

[0023] By making the radial thickness of the first ceramic layer 0.1 mm or more, the strength of the first ceramic layer can be ensured. Furthermore, by making the radial thickness of the first ceramic layer 1.0 mm or less, the thermal conductivity generated by the first resistive heating element can be appropriately maintained. Additionally, by making the radial thickness of the second ceramic layer 0.1 mm or more, the strength of the second ceramic layer can be ensured. Furthermore, by making the radial thickness of the second ceramic layer 1.0 mm or less, the thermal conductivity generated by the second resistive heating element can be appropriately maintained.

[0024] In one aspect of the invention, the medium is a liquid medium, and the ceramic heater (20) is used as a vehicle-mounted heat exchanger.

[0025] Based on this structure, it is possible to provide an on-board heat exchanger that improves the thermal efficiency of ceramic heaters.

[0026] The ceramic heater module (1) of the present invention comprises: the ceramic heater (20) of the present invention; and a housing (10) which houses the ceramic heater and has an inlet (11) and an outlet (12) for the flow of the liquid medium.

[0027] Based on this structure, a ceramic heater module with improved thermal efficiency can be provided.

[0028] The liquid heating device (100) of the present invention includes a control device (36) for controlling the ceramic heater module (1) of the present invention.

[0029] Based on this structure, a liquid heating device with improved thermal efficiency of ceramic heaters can be provided.

[0030] The method for manufacturing the ceramic heater (20) of the present invention comprises: a first step in which a cylindrical precursor ceramic body (51p) is formed; a second step in which a first resistive heating element (62) that heats up by energizing is disposed on at least a portion of the inner peripheral surface of the precursor ceramic body (51p); and a third step in which the precursor ceramic body (51p) on which the first resistive heating element (62) is disposed is fired at a predetermined temperature to produce a ceramic body (51) on which the first resistive heating element (62) is disposed, the ceramic body (51) having a first opening (O1) at one end through which a medium can flow in, and a second opening (O2) at the other end through which the medium can flow out.

[0031] Based on this structure, it is possible to manufacture ceramic heaters with improved thermal efficiency.

[0032] In one aspect of the invention, the second step includes: a step of further fabricating a first green sheet (G1) as a green sheet of a first ceramic layer (52) in a manner that covers the surface of the first resistive heating element (62); and a step of disposing the first green sheet on at least a portion of the inner peripheral surface of the precursor ceramic body. In the third step, the precursor ceramic body on which the first green sheet is further disposed is fired at the predetermined temperature to produce a ceramic body (51) having the first ceramic layer disposed on the surface of the first resistive heating element.

[0033] According to this structure, in the second process, the first green sheet is made by covering the surface of the first resistive heating element, thereby improving the durability of the first resistive heating element.

[0034] In one aspect of the invention, the second step includes the step of providing a second resistive heating element (63) that is heated by energizing at least a portion of the outer peripheral surface of the precursor ceramic body (51p), and in the third step, the precursor ceramic body on which the second resistive heating element is provided is fired at the specified temperature to produce a ceramic body (51) on which the second resistive heating element is provided.

[0035] Based on this structure, by appropriately setting the connection method between the first and second resistive heating elements, it is possible to manufacture a ceramic heater that not only improves thermal efficiency but also significantly reduces the possibility of boiling in a liquid medium.

[0036] In one aspect of the invention, the second step includes: a step of further fabricating a second green sheet (G2) as a green sheet of a second ceramic layer (53) in a manner that covers the surface of the second resistive heating element (63); and a step of disposing the second green sheet on at least a portion of the outer peripheral surface of the precursor ceramic body, wherein in the third step, the precursor ceramic body on which the second green sheet is further disposed is fired at the predetermined temperature to produce a ceramic body (51) on which the second ceramic layer covering the surface of the second resistive heating element is further disposed.

[0037] According to this structure, in the second process, a second green sheet is made by covering the surface of the second resistive heating element, thereby improving the durability of the second resistive heating element. Attached Figure Description

[0038] Figure 1 This is a partial cross-sectional schematic diagram of the heating device of this embodiment.

[0039] Figure 2 yes Figure 1 A cross-sectional view of the ceramic substrate of the ceramic heater in the heating device.

[0040] Figure 3 This is a three-dimensional view of a cylindrical pre-fired ceramic body (first process) before formal firing.

[0041] Figure 4 This is a three-dimensional view of the first green sheet, which serves as the first ceramic layer, and the first resistive heating element disposed therein (second process).

[0042] Figure 5 This is a three-dimensional view of the second green sheet, which serves as the second ceramic layer, and the second resistive heating element disposed therein (second process).

[0043] Figure 6A This is a three-dimensional view showing the state where adhesive is applied to one side of the first green film (second process).

[0044] Figure 6B It means to Figure 6A A three-dimensional image of the first raw sheet being bent into a cylindrical shape by applying external force (second process).

[0045] Figure 6C This diagram illustrates the process of inserting a first green sheet, bent into a cylindrical shape, into a pre-fired ceramic body (second step).

[0046] Figure 6D This diagram illustrates the process of formally bonding the first green sheet, which is temporarily bonded to the inner circumferential surface of the pre-fired ceramic body, using a rod component (second process).

[0047] Figure 7 This diagram illustrates the process of bonding a second green sheet to the outer peripheral surface of a pre-fired ceramic body (second process).

[0048] Explanation of reference numerals in the attached figures

[0049] 1: Ceramic heater module; 10: Housing; 11: Circular hole; 12: Outlet passage; 20: Ceramic heater; 21: Base; 22: Main body; 24, 25, 26, 27: Electrode; 30: Control unit; 33: Power supply; 34, 35: Ammeter; 36: Control device; 37: Inlet temperature sensor; 38: Outlet temperature sensor; 41: Inlet piping; 42: Outlet piping; 51: Ceramic body; 51p: Precursor ceramic body; 52, 53: Ceramic layer; 62, 63: Resistance heating element; 100: Heating device. Detailed Implementation

[0050] The embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1 This is a schematic structural diagram of the heating device 100 according to this embodiment. Figure 1As shown, the heating device 100 includes a ceramic heater module 1 and a control unit 30. This heating device 100 is configured to heat a liquid to a predetermined temperature via the ceramic heater module 1. For ease of explanation, in... Figure 1 The ceramic heater module 1 is illustrated in a partial sectional view. Additionally, the proportions of the components in the accompanying drawings sometimes differ from the actual proportions.

[0051] The ceramic heater module 1 includes a housing 10 and a ceramic heater 20. The housing 10 is a component for forming a flow path for the liquid heated by the ceramic heater 20. The housing 10 is formed as a cylinder closed at both ends. Figure 1 The section containing the axis is represented. A circular hole 11 extending axially is formed in the center of the upper end wall of the housing 10. Additionally, on the side peripheral walls of the housing 10... Figure 1 The upper part of the housing 10 is provided with a cylindrical outlet passage 12. An outlet pipe 42 is connected to the outlet passage 12. Therefore, the internal space of the housing 10 is connected to the outlet pipe 42 via the outlet passage 12. Liquid discharged from the housing 10 flows to the outlet pipe 42. The circular hole 11 corresponds to the inlet of the housing 10, and the outlet passage 12 corresponds to the outlet of the housing 10.

[0052] The ceramic heater 20 has resistance heating elements 62 and 63 (see reference). Figure 2 The ceramic substrate Cb is generally cylindrical, and the flange F is annular. The resistance heating elements 62 and 63 are components that heat up by passing an electric current through them, and are made of relatively long wires to form a prescribed pattern. Tungsten wire can be used as an example of a resistance heating element. The resistance heating elements 62 and 63 are embedded in the ceramic substrate Cb. The ceramic substrate Cb is a component used to heat the object being heated, and is heated by the resistance heating elements 62 and 63 embedded therein. The ceramic substrate Cb is formed of ceramic (typically alumina). The flange F is mounted on the outer periphery of a predetermined portion of the ceramic substrate Cb in a radially outward manner.

[0053] Figure 2 This is a cross-sectional view of the ceramic substrate Cb (strictly speaking, the ceramic substrate Cb in which the resistive heating elements 62 and 63 are embedded). Figure 1 and Figure 2 As shown, the ceramic substrate Cb has a base 21 and a main body 22. The base 21 and the main body 22 are continuously arranged along the axial direction. The base 21 is formed by the upper end portion of the ceramic substrate Cb. The main body 22 is formed by a cylindrical portion excluding the base 21. The base 21 has a portion Pf at its lower end. The portion Pf is a mounting flange F (see reference). Figure 1 The axial length of the main body 22 is longer than that of the base 21. Furthermore, the base 21 and the main body 22 are coaxially cylindrical, and their internal spaces are interconnected axially.

[0054] like Figure 2 As shown, the ceramic substrate Cb is composed of a cylindrical ceramic body 51, a generally cylindrical ceramic layer 52 (first ceramic layer), and a generally cylindrical ceramic layer 53 (second ceramic layer). The upper end of the ceramic body 51 is open at the opening O1 (first opening), and the lower end is open at the opening O2 (second opening). In this embodiment, the radial thickness of the ceramic body 51 is 2.2 mm, but it is not limited to this.

[0055] The ceramic layer 52 is configured to contact the inner peripheral surface of the ceramic body 51, except for its upper end. The upper end of the ceramic layer 52 protrudes upward (exposed to the outside) from the upper end of the ceramic body 51. Electrodes 24 and 25 (refer to the dashed lines) are formed on the outer peripheral surface of this protrusion. In other words, electrodes 24 and 25 are formed on the outer peripheral surface of the base 21. Electrodes 24 and 25 are both made of conductive materials such as metal. The lower end of the ceramic layer 52 is located slightly above the lower end of the ceramic body 51. The outer peripheral surface of the ceramic layer 52 and the inner peripheral surface of the ceramic body 51 are firmly bonded at their contact points by diffusion bonding.

[0056] A gap is formed axially from its upper end to its lower end in a portion of the circumferential direction of the ceramic layer 52 (see reference). Figure 1 The circumferential length of the gap is constant along the entire axial direction. The radial thickness d1 of the ceramic layer 52 is significantly smaller than the radial thickness of the ceramic body 51; in this embodiment, d1 = 0.55 mm. However, the ceramic layer 52 can be formed to any thickness satisfying 0.1 mm ≤ d1 ≤ 1.0 mm, depending on the application of the ceramic heater 20. Furthermore, a heat-resistant reinforcing member can be provided at the protruding portion of the ceramic layer 52 extending from the upper end of the ceramic body 51.

[0057] A resistive heating element 62 (first resistive heating element) is embedded in the ceramic layer 52. Most of the resistive heating element 62 extends on an imaginary cylindrical surface coaxial with the ceramic layer 52. The diameter of this imaginary cylindrical surface is larger than the inner diameter of the ceramic layer 52 but smaller than its outer diameter. That is, the resistive heating element 62 is embedded relatively inwardly in the radial direction of the ceramic substrate Cb. The resistive heating element 62 is embedded in a manner that forms a predetermined pattern in the main body portion 22. Both ends of the resistive heating element 62 are led out to the base portion 21, and their ends are respectively connected to electrodes 24 and 25 formed on the outer peripheral surface of the protruding portion of the ceramic layer 52. Therefore, by applying a predetermined voltage between electrodes 24 and 25, current is supplied to the resistive heating element 62.

[0058] The ceramic layer 53 is disposed in contact with the outer peripheral surface of the ceramic body 51. The upper end of the ceramic layer 53 is located slightly below the upper end of the ceramic body 51. Electrodes 26 and 27 (refer to the dashed lines) are formed on the outer peripheral surface of the upper end of the ceramic layer 53. In other words, electrodes 26 and 27 are formed on the outer peripheral surface of the base 21. Electrodes 26 and 27 are both made of conductive components such as metal. The lower end of the ceramic layer 53 is located slightly above the lower end of the ceramic body 51. The inner peripheral surface of the ceramic layer 53 and the outer peripheral surface of the ceramic body 51 are firmly bonded at their contact portion by diffusion bonding.

[0059] A gap is formed axially from its upper end to its lower end in a portion of the circumferential direction of the ceramic layer 53 (see reference). Figure 1 The circumferential length of the gap is constant along the entire axial direction. In this embodiment, the radial thickness d2 of the ceramic layer 53 is equal to the thickness d1 of the ceramic layer 52 (d2 = 0.55 mm). However, similar to the ceramic layer 52, the ceramic layer 53 can be formed to any thickness satisfying 0.1 mm ≤ d2 ≤ 1.0 mm, depending on the application of the ceramic heater 20.

[0060] A resistive heating element 63 (a second resistive heating element) is embedded in the ceramic layer 53. Most of the resistive heating element 63 extends on an imaginary cylindrical surface coaxial with the ceramic layer 53. The diameter of this imaginary cylindrical surface is larger than the inner diameter of the ceramic layer 53 but smaller than its outer diameter. That is, the resistive heating element 63 is embedded at a relatively outer position in the radial direction of the ceramic substrate Cb. Similar to the resistive heating element 62, the resistive heating element 63 is embedded in a manner forming a predetermined pattern in the main body portion 22. Both ends of the resistive heating element 63 are led out to the base portion 21, and their ends are respectively connected to electrodes 26 and 27 formed on the outer peripheral surface of the upper end of the ceramic layer 53. Therefore, by applying a predetermined voltage between electrodes 26 and 27, current is supplied to the resistive heating element 63.

[0061] In this embodiment, the resistance value R1 of the resistive heating element 62 is equal to the resistance value R2 of the resistive heating element 63 (R1 = R2). However, this structure is not limited to this one, and the resistance values ​​R1 and R2 may also be different from each other.

[0062] return Figure 1 Continuing the explanation, an inlet pipe 41 is connected to the base 21. As described above, a gap is formed in a portion of the circumferential direction of the protruding portion of the ceramic layer 52, so the inlet pipe 41 is inserted into the upper end of the ceramic body 51. Liquid heated by the ceramic heater 20 is introduced from the inlet pipe 41 toward the interior space of the base 21.

[0063] The axial length of the main body 22 is shorter than the axial length of the housing 10. Furthermore, the outer diameter of the main body 22 is approximately equal to the diameter of the circular hole 11 formed in the center of the upper end wall of the housing 10. The main body 22 is inserted into the internal space of the housing 10 from its top end side through the circular hole 11. Thus, the main body 22 is coaxially disposed within the internal space of the housing 10. At this time, the base 21 protrudes upwards from the upper end of the housing 10, and the flange F rests on the upper end face of the housing 10. Additionally, the gap between the upper outer periphery of the main body 22 and the circular hole 11 is liquid-tightly sealed by a sealing member or the like.

[0064] The control unit 30 includes conductive components w1, w2, w3, w4, a power supply device 33, ammeters 34 and 35, a control device 36, an inlet temperature sensor 37, and an outlet temperature sensor 38.

[0065] Conductive components w1 to w4 are all composed of a conductor having one end and another end. Leads can be shown as conductive components w1 to w4. One end of conductive component w3 is connected to electrode 26, and the other end is connected to power supply device 33. One end of conductive component w4 is connected to electrode 27, and the other end is connected to power supply device 33. One end of conductive component w1 is connected to electrode 24, and the other end is connected to conductive component w3. One end of conductive component w2 is connected to electrode 25, and the other end is connected to conductive component w4. That is, resistive heating element 62 and resistive heating element 63 are connected in parallel. Power supply device 33 is configured to apply a predetermined voltage between electrode 24 and electrode 25 and between electrode 26 and electrode 27. Ammeter 34 is installed in the middle of conductive component w2. Ammeter 34 measures the current flowing to conductive component w2. Ammeter 35 is installed in the middle of conductive component w3. Ammeter 35 measures the current flowing to conductive component w3. In addition, ammeter 34 and ammeter 35 can also be installed on conductive member w1 and conductive member w4, respectively.

[0066] An inlet temperature sensor 37 is installed on the inlet pipe 41 and is capable of measuring the temperature of the liquid flowing in the inlet pipe 41. This temperature will also be referred to as the "inlet temperature" below. An outlet temperature sensor 38 is installed on the outlet pipe 42 and is capable of measuring the temperature of the liquid flowing in the outlet pipe 42. This temperature will also be referred to as the "outlet temperature" below.

[0067] The control device 36 controls the ceramic heater 20. Specifically, the control device 36 controls the energizing state (start / stop of energizing, power value) of the resistive heating elements 62 and 63 to ensure that the heating temperature of the liquid heated by the ceramic heater 20 reaches a predetermined target temperature. The control device 36 includes a CPU, ROM, and RAM.

[0068] The ROM of the control device 36 contains a program pre-stored for controlling the energizing state of the resistive heating elements 62 and 63. The CPU of the control device 36 reads the program from the ROM, loads it into the RAM, and executes it.

[0069] Ammeters 34 and 35 send current signals representing the measured current values ​​to control device 36. Control device 36 obtains the current flowing to conductive member w2 based on the current signal received from ammeter 34, and obtains the current flowing to conductive member w3 based on the current signal received from ammeter 35. Additionally, inlet temperature sensor 37 measures the inlet temperature and sends a temperature signal representing the measured temperature to control device 36. Control device 36 obtains the inlet temperature based on the temperature signal received from inlet temperature sensor 37. Outlet temperature sensor 38 measures the outlet temperature and sends a temperature signal representing the measured temperature to control device 36. Control device 36 obtains the outlet temperature based on the temperature signal received from outlet temperature sensor 38. Control device 36 can also receive signals other than those described above. Control device 36 is configured to control power supply device 33 based on various input signals (current signals, temperature signals, etc.). By controlling power supply device 33 through control device 36, the energizing state of resistive heating element 62 and resistive heating element 63 is controlled. Furthermore, power supply device 33 can also be integrated into control device 36.

[0070] In this embodiment, the heating device 100 with the above-described structure heats the liquid medium flowing in a flow path within a device mounted in a vehicle (hereinafter referred to as "vehicle-mounted device"). In this case, the ceramic heater 20 functions as a heat exchanger (i.e., a vehicle-mounted heat exchanger) for heating the liquid medium flowing in the flow path within the vehicle-mounted device. Examples of vehicle-mounted devices include vehicle air conditioning systems and heaters for vehicle batteries. Examples of flow paths within the vehicle-mounted device include flow paths in the refrigerant circuit of a vehicle air conditioning system and flow paths formed in a heater for a vehicle battery. In this case, the ceramic heater 20 functions as a heat exchanger for heating the refrigerant flowing in the refrigerant circuit of a vehicle air conditioning system, or for heating the fluid flowing in the flow path formed in the heater for a vehicle battery. Furthermore, vehicles include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and fuel cell vehicles.

[0071] In the heating device 100 with the above structure, the liquid, which is the heated body, is introduced into the interior of the base 21 of the ceramic heater 20 from the inlet pipe 41, and then introduced into the interior space of the main body 22 from the base 21.

[0072] Liquid introduced into the internal space of the main body 22, such as Figure 1As shown by the arrow, the liquid flows downwards within the main body 22 and exits from the opening at the top (bottom) end of the main body 22. The space between the inner circumferential surface of the side wall of the housing 10 and the outer circumferential surface of the main body 22 is as follows... Figure 1 As indicated by the arrow, the liquid flows upwards and is discharged through the outlet passage 12 to the outlet pipe 42. In this way, a flow path for the liquid is formed through the housing 10 until the liquid introduced (supplied) from the inlet pipe 41 is discharged to the outlet pipe 42.

[0073] When the liquid flows within the housing 10, the control device 36 controls the power supply device 33 by applying a predetermined voltage between electrodes 24 and 25 and between electrodes 26 and 27. This energizes the resistive heating elements 62 and 63 respectively. The resistive heating elements 62 and 63 generate heat through this energization. The heating of the resistive heating elements 62 and 63 heats the main body 22. More specifically, the heating of the resistive heating element 62 primarily heats the inner peripheral surface of the main body 22, and the heating of the resistive heating element 63 primarily heats the outer peripheral surface of the main body 22. Thus, the liquid flowing on the surfaces (inner and outer peripheral surfaces) of the heated main body 22 is heated by the main body 22. In this way, the liquid is heated by the heating device 100 (ceramic heater 20), and the heated liquid is discharged to the outlet pipe 42.

[0074] The control device 36 obtains the temperature of the liquid before it is heated by the heating device 100 as the inlet temperature based on the temperature signal sent from the inlet temperature sensor 37 installed on the inlet pipe 41. Similarly, the control device 36 obtains the temperature of the liquid after it has been heated by the heating device 100 as the outlet temperature based on the temperature signal sent from the outlet temperature sensor 38 installed on the outlet pipe 42. Then, the control device 36 controls the power supply device 33 to make the outlet temperature match the target temperature. Thus, the temperature of the liquid can be controlled so that the temperature of the liquid discharged into the outlet pipe 42 is the predetermined target temperature. In this case, the control device 36 can control the liquid temperature using PI control based on the deviation between the outlet temperature and the target temperature, so that the outlet temperature is close to the target temperature.

[0075] When the heating device 100 is operating normally, the entire surface of the main body 22 is in contact with the liquid introduced into the heating device 100. Therefore, the main body 22 is heated by the resistance heating elements 62 and 63, and cooled by the liquid flowing over its surface. Consequently, the surface temperature of the main body 22 rises sharply immediately after the energization of the resistance heating elements 62 and 63, but quickly approaches a temperature at which heating and cooling have reached equilibrium, and eventually remains at a relatively constant temperature. Furthermore, the liquid is heated by the main body 22, whose surface temperature is maintained at a relatively constant temperature.

[0076] Next, the manufacturing method of the ceramic heater 20 will be described. The manufacturing method includes a pre-fired ceramic body making process, a green sheet making process, a green sheet bonding process, a firing process, and a flange mounting process. The ceramic heater 20 is manufactured by performing these processes sequentially.

[0077] (Pre-fired ceramic body manufacturing process)

[0078] In this process, the production Figure 3 The pre-fired ceramic body 51p (precursor ceramic body) is shown. Specifically, a material mainly containing alumina is prepared and extruded to form a cylindrical component. The cylindrical component is then tumble-dried, cut to a specified length, and pre-fired at 700°C to 800°C. This process degreases the internal binder and other components of the cylindrical component, increasing its rigidity. Next, both ends are cut with the axial length of the cylindrical component becoming L, and chamfering is performed appropriately, thus producing the pre-fired ceramic body 51p. One end of the pre-fired ceramic body 51p has an opening at opening O1, and the other end has an opening at opening O2. This process is equivalent to an example of the "first process".

[0079] (Raw film production process)

[0080] In this process, the production Figure 4 The raw film G1 shown Figure 5 The image shown is raw film G2. The following sections will explain each section in turn. For example... Figure 4 As shown, the green sheet G1 is configured to include green sheet 521 and green sheet 522. The fabrication steps of green sheet G1 are as follows. First, a slurry is prepared by mixing materials mainly containing alumina, and green sheet 521 with a thickness of 0.05 mm and green sheet 522 with a thickness of 0.59 mm are fabricated using a doctor blade method. Green sheets 521 and 522 are fabricated to be the same size and shape when viewed from above.

[0081] Next, a resistive heating element 62 is patterned on one side 522a of the raw film 522. Figure 4(Illustrated in dashed lines), and on another side 522b, two conductive terminal portions T1 are patterned. The resistive heating element 62 is configured to include two terminal connection portions 62a, two lead-out portions 62b, and a heater portion 62c. The two terminal connection portions 62a are rectangular and are spaced apart along the short side of the green sheet 522. The two terminal portions T1 are smaller rectangular than the terminal connection portions 62a and are spaced apart along the aforementioned short side. The centers of the two terminal connection portions 62a and the two terminal portions T1 are approximately aligned when viewed from above. In the green sheet 522, a through hole (not shown) is pre-formed by punching a hole approximately in the center of the terminal connection portion 62a. During the pattern printing, the resistive heating element 62 is also printed on the inner circumferential surface of the through hole. Thus, the terminal connection portions 62a and the terminal portions T1 are electrically connected via the through hole.

[0082] The two leads 62b are straight and extend along the length of the green sheet 522. One lead 62b connects a terminal connection 62a to the heater section 62c, and the other lead 62b connects another terminal connection 62a to the heater section 62c. The terminal connection 62a and the lead 62b are formed in the region corresponding to the base 21 after the ceramic heater 20 is completed.

[0083] The heater section 62c occupies most of the resistive heating element 62. The resistance value R1 of the resistive heating element 62 can be determined based on the pattern of the heater section 62c (the thickness and length of the printed metal lines). The heater section 62c is formed in the area corresponding to the main body 22 after the ceramic heater 20 is completed.

[0084] Simultaneously, two sets of pads (not shown) are patterned on one side 521b of the green sheet 521. These two sets of pads are positioned to overlap the aforementioned through-hole when the green sheets 521 and 522 are overlapped in the thickness direction. Then, the green sheet 521 is placed on the green sheet 522 with its surface 521b in contact with its surface 522a, and hot-pressed using a rubber press. This produces the green sheet G1 (strictly speaking, the green sheet G1 with the embedded resistive heating element 62). The green sheet G1 is a thin, flat, flexible component. The length L1 of the green sheet G1 in its long side direction is longer than that of the pre-fired ceramic body 51p (see reference). Figure 3 It is manufactured in a manner in which the axial length L is longer (L1>L) and the length L2 of its short side is shorter than the inner circumference of the pre-fired ceramic body 51p.

[0085] Next, the raw film G2 will be explained. For example... Figure 5As shown, green sheet G2 is configured to include green sheet 531 and green sheet 532. The manufacturing steps of green sheet G2 are largely the same as those of green sheet G1, so repeated descriptions are omitted. Green sheets 531 and 532 are made using the same paste as green sheets 521 and 522 and are produced by a scraping method. However, the paste used for green sheets 531 and 532 can also be prepared with a different formulation than that used for green sheets 521 and 522. The thickness of green sheet 531 is equal to the thickness of green sheet 521 (i.e., 0.05 mm), and the thickness of green sheet 532 is equal to the thickness of green sheet 522 (i.e., 0.59 mm). Green sheets 531 and 532 are manufactured to have the same size and shape when viewed from above.

[0086] Next, a resistive heating element 63 is patterned on one side 532a of the raw film 532. Figure 5 (Illustrated in dashed lines), and on another side 532b, two conductive terminal portions T2 are patterned. The resistive heating element 63 is configured to include two terminal connection portions 63a, two lead-out portions 63b, and a heater portion 63c. The pattern of the resistive heating element 63 is similar to that of the resistive heating element 62. The terminal connection portions 63a and the terminal portions T2 are electrically connected via a through hole formed approximately in the center of the terminal connection portions 63a. The heater portion 63c occupies most of the resistive heating element 63, and its pattern determines the resistance value R2 of the resistive heating element 63. One lead-out portion 63b connects one terminal connection portion 63a to the heater portion 63c, and another lead-out portion 63b connects another terminal connection portion 63a to the heater portion 63c. The terminal connection portions 63a and the lead-out portions 63b are formed in the region corresponding to the base 21 after the ceramic heater 20 is completed, and the heater portion 63c is formed in the region corresponding to the main body 22 after the ceramic heater 20 is completed.

[0087] Simultaneously, two sets of pads (not shown) are patterned and printed on one side 531b of the green sheet 531. Then, the green sheets 531 and 532 are heat-pressed together using a rubber press, with surfaces 531b and 532a in contact. This produces the green sheet G2 (strictly speaking, the green sheet G2 with the embedded resistive heating element 63). The green sheet G2 is a thin, flat, flexible component. The length L3 of the green sheet G2 in its long side direction is greater than that of the pre-fired ceramic body 51p (see reference). Figure 3 It is manufactured in a manner in which the axial length L of the pre-fired ceramic body 51p is shorter (L3 < L) and the length L4 of its short side is shorter than the outer periphery of the pre-fired ceramic body 51p.

[0088] (Raw sheet bonding process)

[0089] In this process, green sheet G1 and green sheet G2 are bonded to the pre-fired ceramic body 51p. Specifically, firstly, as... Figure 6AAs shown, the green sheet G1 is arranged with surface 521a (the other side of the green sheet 521) facing downwards, and adhesive A is applied to a portion of surface 522b by screen printing. Figure 6A (Illustrated in grayscale). Adhesive A is applied to the entire area from one end in the longitudinal direction (the end opposite to the side where the terminal portion T1 is formed) to the position where the length L5 is separated in the longitudinal direction. That is, adhesive A is not applied to the area where the terminal portion T1 is formed. The length L5 is slightly shorter than the axial length L of the pre-fired ceramic body 51p (L5 < L).

[0090] Next, as Figure 6B As shown, an external force is applied to the green sheet G1 using an external device (not shown), causing the green sheet G1 to flex into a cylindrical shape. The green sheet G1 flexes with surface 522b as its outer circumferential surface and its length direction aligned with the axial direction. Alternatively, this operation can also be performed manually.

[0091] Next, as Figure 6C As shown, a cylindrical green sheet G1, while being held in shape by an external device, is inserted to a predetermined length into the through hole of the pre-fired ceramic body 51p. In this embodiment, the cylindrical green sheet G1 is inserted from the top end on the side opposite to where the terminal portion T1 is formed, but the insertion direction is not limited to this. The cylindrical green sheet G1 is inserted into the through hole of the pre-fired ceramic body 51p while maintaining a coaxial state. The outer circumference of the cylindrical green sheet G1 is L2, which is shorter than the inner circumference of the pre-fired ceramic body 51p. Therefore, by inserting it in this way, it is possible to prevent the adhesive A from adhering to the inner circumferential surface of the pre-fired ceramic body 51p. The axial length L5 of the portion of the cylindrical green sheet G1 coated with adhesive A is shorter than the axial length L of the pre-fired ceramic body 51p, so that the adhesive A will not be exposed to the outside after insertion. Alternatively, the insertion operation can also be performed manually.

[0092] Next, as Figure 6D As shown, the external force applied to the cylindrical green sheet G1 is released. Then, through a reaction, the cylindrical green sheet G1 returns to its original shape, during which its outer circumferential surface contacts the inner circumferential surface of the pre-fired ceramic body 51p. Thus, the outer circumferential surface of the generally cylindrical green sheet G1 is temporarily bonded to the inner circumferential surface of the pre-fired ceramic body 51p using adhesive A. Next, the rod member 80 is inserted into the through hole, and while applying a radially outward force to the inner circumferential surface of the green sheet G1, it is rotated, thereby formally bonding the temporarily bonded green sheet G1 to the pre-fired ceramic body 51p. Alternatively, this operation can also be performed manually.

[0093] Then, on side 531a of raw sheet G2 (the other side of raw sheet 531). See Figure 5Adhesive A is applied evenly to the surface of the pre-fired ceramic body 51p, to which the green sheet G1 is bonded, by screen printing. This allows the pre-fired ceramic body 51p to rotate approximately one revolution on surface 531a (illustration omitted). Thus, as... Figure 7 As shown, the inner circumferential surface of the generally cylindrical green sheet G2 is bonded to the outer circumferential surface of the pre-fired ceramic body 51p. The axial length L3 of the generally cylindrical green sheet G2 is shorter than the axial length L of the pre-fired ceramic body 51p, so the two ends of the pre-fired ceramic body 51p are slightly exposed from the generally cylindrical green sheet G2.

[0094] The raw film production process and the raw film bonding process are equivalent to an example of the "second process".

[0095] (Firing process)

[0096] In this process, the pre-fired ceramic body 51p, to which green sheets G1 and G2 are bonded, is formally fired at a temperature of 1300°C to 1500°C. Thus, the pre-fired ceramic body 51p, green sheets G1, and green sheets G2 become ceramic body 51, ceramic layer 52, and ceramic layer 53, respectively. The contact surfaces of ceramic body 51 and ceramic layers 52 and 53 are firmly bonded through diffusion bonding. In this way, a ceramic substrate Cb in which resistive heating elements 62 and 63 are embedded is produced. This firing process is equivalent to an example of the "third process".

[0097] (Flange installation process)

[0098] In this process, an annular flange F is installed on the portion Pf of the ceramic substrate Cb (refer to...). Figure 1 Specifically, first, a flange F is prepared, which penetrates the ceramic substrate Cb through a through hole. The flange F is then fixed at a portion of Pf, thus enabling installation. Through these steps, the product is manufactured... Figure 1 and Figure 2 The ceramic heater 20 shown.

[0099] As explained above, in the ceramic heater 20 of this embodiment, a resistance heating element 62 is provided at a relatively inner position in the radial direction of the ceramic substrate Cb. According to this structure, the heat generated by the resistance heating element 62 is more easily transferred to the inner circumferential surface of the ceramic substrate Cb compared to the outer circumferential surface. Therefore, from the viewpoint of the temperature rise of the liquid caused by the resistance heating element 62, the liquid is more easily heated during its flow on the inner circumferential surface compared to the period during which it flows on the outer circumferential surface of the ceramic substrate Cb (main body 22). Here, generally in a cylindrical heating element, the thermal efficiency of heating the medium flowing on the inner circumferential surface of the heating element is higher than the thermal efficiency of heating the medium flowing on the outer circumferential surface of the heating element. Therefore, according to the ceramic heater 20, thermal efficiency can be improved compared to conventional ceramic heaters (i.e., ceramic heaters where the resistance heating element is only provided at a relatively outer position in the radial direction of the ceramic substrate Cb).

[0100] In particular, in the ceramic heater 20 of this embodiment, a resistance heating element 63 is also provided at a relatively outer position in the radial direction of the ceramic substrate Cb, and the resistance heating elements 62 and 63 are connected in parallel. If a conventional ceramic heater having a resistance heating element with a resistance value equal to the combined resistance value of the resistance heating elements 62 and 63 is provided only at a relatively outer position in the radial direction of the ceramic substrate Cb, then when the same voltage is applied to the ceramic heater 20 and the ceramic heater P, the power in each of the resistance heating elements 62 and 63 becomes half the power in the resistance heating elements of the ceramic heater P. According to this structure, compared with the ceramic heater P, the ceramic heater 20 can reduce the power density (energy density per unit time) of the ceramic substrate Cb, thus improving the thermal efficiency of the liquid and significantly reducing the possibility of liquid boiling. As a result, the generation of ceramic heater cracks caused by boiling can be suppressed.

[0101] Furthermore, by making the radial thickness of ceramic layer 52 0.1 mm or more, the strength of ceramic layer 52 can be ensured. Additionally, by making the radial thickness of ceramic layer 52 1.0 mm or less, the thermal conductivity generated by the resistive heating element 62 can be appropriately maintained. Similarly, by making the radial thickness of ceramic layer 53 0.1 mm or more, the strength of ceramic layer 53 can be ensured. Additionally, by making the radial thickness of ceramic layer 53 1.0 mm or less, the thermal conductivity generated by the resistive heating element 63 can be appropriately maintained.

[0102] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. Various modifications can be made as long as they do not depart from the purpose of the present invention.

[0103] Furthermore, this disclosure can include the following methods. [1]

[0105] A ceramic heater comprises: a ceramic body, which is cylindrical, having a first opening at one end through which a medium can flow in, and a second opening at the other end through which the medium can flow out; and a first resistive heating element disposed on at least a portion of the inner circumferential surface of the ceramic body, which heats up by energizing. [2]

[0107] The ceramic heater according to [1] further comprises a first ceramic layer covering the surface of the first resistive heating element. [3]

[0109] The ceramic heater according to [1] or [2] further comprises a second resistive heating element disposed on at least a portion of the outer peripheral surface of the ceramic body, which heats up by energizing. [4]

[0111] The ceramic heater according to [3] further comprises a second ceramic layer covering the surface of the second resistive heating element. [5]

[0113] According to the ceramic heater described in [2], the radial thickness of the first ceramic layer is more than 0.1 mm and less than 1.0 mm. [6]

[0115] According to the ceramic heater described in [4], the radial thickness of the second ceramic layer is more than 0.1 mm and less than 1.0 mm. [7]

[0117] The ceramic heater according to any one of [1] to [6] is a liquid medium and is used as a vehicle-mounted heat exchanger. [8]

[0119] A ceramic heater module comprising: a ceramic heater as described in any one of [1] to [7]; and a housing that houses the ceramic heater and has an inlet and an outlet for the flow of the liquid medium. [9]

[0121] A liquid heating device, comprising a control device for controlling the ceramic heater module described in [8].

[10]

[0123] A method for manufacturing a ceramic heater includes: a first step in which a cylindrical precursor ceramic body is formed; a second step in which a first resistive heating element, which heats up when energized, is disposed on at least a portion of the inner peripheral surface of the precursor ceramic body; and a third step in which the precursor ceramic body on which the first resistive heating element is disposed is fired at a predetermined temperature to produce a ceramic body on which the first resistive heating element is disposed, the ceramic body having a first opening at one end through which a medium can flow in, and a second opening at the other end through which the medium can flow out.

[11]

[0125] According to the method for manufacturing a ceramic heater as described in

[10] , the second step includes: a step of further producing a first green sheet as a first ceramic layer in a manner that covers the surface of the first resistive heating element; and a step of disposing the first green sheet on at least a portion of the inner circumferential surface of the precursor ceramic body. In the third step, the precursor ceramic body on which the first green sheet is further disposed is fired at the predetermined temperature to produce a ceramic body having a first ceramic layer disposed on the surface of the first resistive heating element.

[12]

[0127] According to the manufacturing method of the ceramic heater described in

[10] or

[11] , the second step includes a step of providing a second resistive heating element that heats up by energizing at least a portion of the outer peripheral surface of the precursor ceramic body, and in the third step, the precursor ceramic body on which the second resistive heating element is provided is fired at the specified temperature to produce a ceramic body on which the second resistive heating element is provided.

[13]

[0129] According to the method for manufacturing a ceramic heater as described in

[12] , the second step includes: a step of further producing a second green sheet as a second ceramic layer in a manner that covers the surface of the second resistive heating element; and a step of disposing the second green sheet on at least a portion of the outer peripheral surface of the precursor ceramic body, wherein in the third step, the precursor ceramic body on which the second green sheet is further disposed is fired at the predetermined temperature to produce a ceramic body on which the second ceramic layer covering the surface of the second resistive heating element is further disposed.

Claims

1. A ceramic heater, wherein, This ceramic heater has the following features: A ceramic body, which is cylindrical, has a first opening at one end allowing a medium to flow in, and a second opening at the other end allowing the medium to flow out; and A first resistive heating element is disposed on at least a portion of the inner peripheral surface of the ceramic body and heats up when energized.

2. The ceramic heater according to claim 1, wherein, The ceramic heater also has a first ceramic layer covering the surface of the first resistive heating element.

3. The ceramic heater according to claim 1 or 2, wherein, The ceramic heater also includes a second resistive heating element disposed on at least a portion of the outer peripheral surface of the ceramic body, which generates heat by energizing the ceramic body.

4. The ceramic heater according to claim 3, wherein, The ceramic heater also has a second ceramic layer covering the surface of the second resistive heating element.

5. The ceramic heater according to claim 2, wherein, The radial thickness of the first ceramic layer is greater than 0.1 mm and less than 1.0 mm.

6. The ceramic heater according to claim 4, wherein, The radial thickness of the second ceramic layer is greater than 0.1 mm and less than 1.0 mm.

7. The ceramic heater according to claim 1 or 2, wherein, The medium is a liquid medium, and the ceramic heater is used as a vehicle-mounted heat exchanger.

8. A ceramic heater module, wherein, The ceramic heater module comprises: the ceramic heater of claim 7; and a housing that houses the ceramic heater and has an inlet and an outlet for the flow of the liquid medium.

9. A liquid heating device, wherein, The liquid heating device includes a control device for controlling the ceramic heater module as described in claim 8.

10. A method for manufacturing a ceramic heater, wherein, This manufacturing method has the following features: The first step involves forming a cylindrical precursor ceramic body. In the second step, a first resistive heating element that generates heat by energizing is disposed on at least a portion of the inner peripheral surface of the precursor ceramic body. as well as In the third step, the precursor ceramic body with the first resistive heating element is fired at a specified temperature to produce a ceramic body with the first resistive heating element. The ceramic body has a first opening at one end through which a medium can flow in, and a second opening at the other end through which the medium can flow out.

11. The method for manufacturing a ceramic heater according to claim 10, wherein, The second step includes: a step of further fabricating a first green sheet as a first ceramic layer in a manner that covers the surface of the first resistive heating element; and a step of disposing the first green sheet on at least a portion of the inner peripheral surface of the precursor ceramic body. In the third step, the precursor ceramic body, on which the first green sheet is further disposed, is fired at the specified temperature to produce a ceramic body having a first ceramic layer disposed on the surface of the first resistive heating element.

12. The method for manufacturing a ceramic heater according to claim 10 or 11, wherein, The second step includes the step of further providing a second resistive heating element that heats up when energized on at least a portion of the outer peripheral surface of the precursor ceramic body. In the third step, the precursor ceramic body, which is also provided with the second resistive heating element, is fired at the specified temperature to produce a ceramic body that is also provided with the second resistive heating element.

13. The method for manufacturing a ceramic heater according to claim 12, wherein, The second step includes: a step of further fabricating a second green sheet as a second ceramic layer in a manner that covers the surface of the second resistive heating element; and a step of disposing the second green sheet on at least a portion of the outer peripheral surface of the precursor ceramic body. In the third step, the precursor ceramic body, on which the second green sheet is further disposed, is fired at the specified temperature to produce a ceramic body on which a second ceramic layer is further disposed covering the surface of the second resistive heating element.

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