Heater control device and heating device

Abstract

To provide a heater control device and a heating device that can suppress a decrease in the thermal efficiency of a heater that heats a liquid.SOLUTION: A heater control device monitors the temperature of a liquid flowing through a flow path and controls a heater that is placed in a heater unit provided in the flow path and heats the liquid to a target temperature. When the heater is controlled to raise the temperature of the liquid, and the heater control device determines that the liquid has reached an over-boiling state in which excessive evaporation of the liquid occurs at the interface between the heater and the liquid, the heater control device reduces the output of the heater to the extent that the liquid can still be heated.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to a heater control device and a heating device. [Background technology]

[0002] A ceramic heater for heating fluid is known from Japanese Patent Application Laid-Open No. 2006-236617 (Patent Document 1 below). This ceramic heater is cylindrical and has a heating element formed in a serpentine shape inside. Hot water is generated by passing water through the cylindrical ceramic heater while an electric current is passed through the heating element.

[0003] When water is heated by a ceramic heater, air bubbles may be generated on the surface of the ceramic heater. If such air bubbles continue to adhere to the surface of the ceramic heater, heat is not transferred from the ceramic heater to the water in the area in contact with the air bubbles, and the temperature of the ceramic heater rises excessively. If the air bubbles detach from the surface of the ceramic heater, low-temperature water comes into contact with the high-temperature ceramic heater surface, causing a thermal shock to the ceramic heater, which may damage the ceramic heater. In Patent Document 1, a hydrophilic coating layer is formed on the surface of the ceramic heater to prevent air bubbles from adhering to the ceramic heater surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-236617 A Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, it is assumed that the ceramic heater will be applied to a warm water washing toilet seat, etc. However, when a ceramic heater with high power consumption is used to generate a higher temperature liquid, the liquid is vaporized more actively, and air bubbles are more likely to be generated on the ceramic heater surface, so it is considered that the above configuration cannot sufficiently suppress the adhesion of air bubbles to the ceramic heater surface. Therefore, there may be cases where the ceramic heater cannot be sufficiently prevented from being damaged by thermal shock.

[0006] In addition, when heating liquid with a heater that consumes a large amount of power, including ceramic heaters, bubbles may be generated on the heater surface and grow, reducing the contact area between the liquid and the heater and decreasing the thermal efficiency. In addition, the flowing noise of the bubbles may become a problem.

[0007] The present disclosure has been completed in light of the above-mentioned circumstances, and aims to provide a heater control device and a heating device that can suppress a decrease in the thermal efficiency of a heater that heats a liquid. [Means for solving the problem]

[0008] The heater control device disclosed herein is a heater control device that monitors the temperature of a liquid flowing through a flow path and controls a heater that is placed in the flow path and heats the liquid to a target temperature.When the heater is controlled to raise the temperature of the liquid, and it is determined that the liquid has reached an overboiling state in which excessive evaporation of the liquid occurs at the interface between the heater and the liquid, the heater control device reduces the output of the heater to the extent that the temperature of the liquid can be raised.

[0009] The heating device of the present disclosure is a heating device including a flow path through which a liquid flows, a heater disposed in the flow path, a thermometer that measures the temperature of the liquid, and the above-mentioned heater control device. Effect of the Invention

[0010] According to the present disclosure, it is possible to provide a heater control device and a heating device that can suppress a decrease in the thermal efficiency of a heater that heats a liquid. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram that illustrates a vehicle interior heating device including a heating device according to a first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the heating device of the first embodiment. [Diagram 3] FIG. 3 is an explanatory diagram for explaining the overboiling state. [Figure 4] FIG. 4 is a graph illustrating conventional heater control. [Diagram 5] FIG. 5 is a graph illustrating heater control in the first embodiment. [Figure 6] FIG. 6 is a flowchart showing a procedure for controlling the heater in the first embodiment. [Figure 7] FIG. 7 is a graph illustrating heater control in the second embodiment. [Figure 8] FIG. 8 is a flowchart showing a procedure for controlling the heater in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. (1) The heater control device disclosed herein is a heater control device that monitors the temperature of a liquid flowing through a flow path and controls a heater that is placed in the flow path and heats the liquid to a target temperature. When the heater is controlled to raise the temperature of the liquid and it is determined that the liquid has reached an over-boiling state in which excessive evaporation of the liquid occurs at the interface between the heater and the liquid, the heater control device reduces the output of the heater to the extent that the temperature of the liquid can be raised.

[0013] With this configuration, the temperature of the liquid can be efficiently increased while preventing excessive evaporation of the liquid at the interface between the heater and the liquid.

[0014] (2) In the heater control device described in (1), it is preferable that the current value and voltage value of the heater can be acquired, and when it is determined that the overboiling state has been reached, an upper limit value of the heater output is set according to the temperature of the liquid.

[0015] According to this configuration, by setting the upper limit of the heater output in accordance with the temperature of the liquid, it is possible to efficiently raise the temperature of the liquid while further suppressing excessive evaporation of the liquid.

[0016] (3) In the heater control device described in (2), it is preferable that a flow rate of the liquid flowing through the flow path can be obtained, and the upper limit value of the output of the heater is set taking the flow rate into consideration.

[0017] With this configuration, the upper limit of the heater output can be set more accurately.

[0018] (4) In the heater control device described in (1), the resistance value of the heater is acquireable, an average value and a current value of the resistance value are acquired, and when the difference between the average value and the current value becomes equal to or greater than a predetermined value, it is determined that the over-boiling state has been reached.

[0019] With this configuration, it is possible to determine whether the over-boiling state has been reached based on the magnitude of the difference between the average heater resistance value and the current resistance value.

[0020] (5) In the heater control device described in any one of (1) to (4), the heater is preferably a ceramic heater.

[0021] According to this configuration, by suppressing the output of the ceramic heater in an overboiling state, it is possible to prevent the overheated ceramic heater from coming into contact with the liquid and being damaged.

[0022] (6) The heating device of the present disclosure is a heating device having a flow path through which a liquid flows, a heater disposed within the flow path, a thermometer that measures the temperature of the liquid, and a heater control device described in any one of (1) to (5).

[0023] With this configuration, it is possible to provide a heating device that can efficiently heat the liquid.

[0024] [Details of the First Embodiment of the Present Disclosure] A first embodiment of the present disclosure will be described with reference to Figures 1 to 6. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0025] <Heating device> The heating device 10 of the present disclosure is a device for heating liquid such as water. The heating device 10 is installed in, for example, an electric vehicle (EV) and is used for heating the vehicle interior and keeping the battery warm. FIG. 1 illustrates a vehicle interior heating device 1 using the heating device 10. The vehicle interior heating device 1 includes the heating device 10, a circulation circuit 2, a heat exchanger 3 provided in the circulation circuit 2, a flowmeter 4, a thermometer 5, a pump (not shown), a blower 6, and the like. Water is circulated through the circulation circuit 2 by the pump. The flow rate of the water is measured by the flowmeter 4. The thermometer 5 is disposed upstream of the heating device 10 and measures the temperature of the water before being heated by the heating device 10 (hereinafter referred to as the inlet water temperature). The blower 6 supplies air into the vehicle interior through the heat exchanger 3. The water heated by the heating device 10 passes through the circulation circuit 2 and is supplied to the heat exchanger 3. The heat exchanger 3 is used, for example, in a heat pump type air conditioner. If the temperature of the heat exchanger 3 drops due to a drop in the outside air temperature, the function of the heat pump will decrease, so the heated water suppresses the temperature drop of the heat exchanger 3. Heat is exchanged between the air sent in by the blower 6 and the heat exchanger 3, and the heated air is sent into the vehicle interior.

[0026] <Heater> FIG. 2 is a schematic cross-sectional view of the heating device 10. The heating device 10 includes a cylindrical heater 11, a thermometer 12, a heater control device 13 for controlling the heater 11, and a housing 14. The heater 11 of this embodiment is a ceramic heater. The heater 11 includes a cylindrical member and a heating resistor formed inside the cylindrical member. The cylindrical member is mainly made of a ceramic material such as alumina. The heating resistor is made of a metal such as tungsten and has a meandering thin wire shape. The heating resistor generates heat when a voltage is applied from a power supply device. The heater 11 can be manufactured, for example, by sandwiching a metal pattern that becomes the heating resistor between ceramic green sheets, winding the metal pattern around a rod-shaped mold material, and firing the mold material.

[0027] <Heater control device> The heater control device 13 of this embodiment is configured by, for example, a control board. In addition to a control unit such as a CPU, the control board is provided with a power supply device, a FET, a voltage detection unit, a current detection unit, and the like. The power supply device applies a voltage to a heater circuit including the heater 11. The FET turns on and off the application of voltage to the heater 11. The voltage detection unit is capable of acquiring a voltage value applied to both sides of the heater 11 in the heater circuit. The current detection unit is capable of acquiring a current value flowing through the heater 11. In addition, the control unit is capable of acquiring an inlet water temperature measured by the thermometer 5, a water temperature (outlet water temperature described later) measured by the thermometer 12, and a water flow rate measured by the flowmeter 4. The control of the heater 11 by the heater control device 13 will be described later.

[0028] The heating device 10 has a flow path 15 through which water flows. The flow path 15 includes a first space 11A provided inside the heater 11 and a second space 14A provided between the housing 14 and the heater 11. The heater 11 is disposed so as to be in contact with both the first space 11A and the second space 14A. One end of the flow path 15 is an inlet 15A through which water is introduced into the heating device 10, and the other end of the flow path 15 is an outlet 15B through which water is discharged to the outside of the heating device 10. As shown by the arrows, the water introduced from the inlet 15A passes through the first space 11A, the second space 14A, and is discharged from the outlet 15B.

[0029] Housing 14 is made of, for example, resin or metal. Housing 14 has thermometer holding portion 14B that holds thermometer 12, and board housing portion 14C that houses a control board. Thermometer holding portion 14B is disposed in flow path 15 downstream of heater 11. Therefore, thermometer 12 measures the temperature of water heated by heater 11 (hereinafter referred to as outlet water temperature).

[0030] <Overboiling state> FIG. 3 is a schematic diagram showing an enlarged area enclosed by a dashed line in FIG. 2. The heating device 10 of this embodiment is provided with a heater 11 capable of rapidly generating high-temperature water. This makes it easier for bubbles to be generated and grow locally on the surface of the heater 11. When the temperature of the water rises and bubbles are actively generated, the contact area between the water and the heater 11 decreases, which may result in a decrease in thermal efficiency. This state in which excessive vaporization of water occurs at the interface between the heater 11 and the water is referred to as an overboiling state. In an overboiling state, the flowing noise of bubbles may also be a problem.

[0031] In particular, the heater 11 of this embodiment is a ceramic heater, and in an overboiling state, the heater 11 may be damaged by thermal shock. For example, in FIG. 3, the region A1 with bubbles attached to the surface of the heater 11 is not in contact with water and cannot transfer heat to the water, so it becomes overheated. Then, when the bubbles grow to a certain extent, they leave the region A1. Then, the overheated region A1 comes into contact with relatively low-temperature water, and a temperature difference occurs instantaneously in the region A1. When this temperature difference exceeds a predetermined value, the ceramic material constituting the region A1 is damaged due to the thermal expansion difference. In the graphs of FIG. 4 and FIG. 5, the temperature region where overboiling may occur is called the overboiling region.

[0032] In the conventional heater control method, for example, the heater power may be kept constant until the water temperature reaches the target temperature. In such a case, the generation and growth of bubbles cannot be suppressed in the overboiling region, and as described above, problems such as a decrease in thermal efficiency, generation of bubble flow noise, and damage to the heater when a ceramic heater is used are likely to occur. Therefore, the heater control device 13 of this embodiment suppresses application of an excessive voltage to the heater 11 in the overboiling region. Specifically, the heater control device 13 reduces the power of the heater 11 to a level lower than that before the overboiling region is reached, within a range in which the water temperature can be increased.

[0033] <Detection of overboiling> In this embodiment, whether or not the water is in an overboiling state is determined by the water temperature. Specifically, an experiment is conducted in advance to obtain data on the correlation between the water temperature and the size and number of bubbles on the surface of the heater 11, and a water temperature threshold value at which it can be determined that the water has reached an overboiling state is set. Here, the outlet water temperature or the inlet water temperature is used as the water temperature. The control unit of the heater control device 13 acquires the water temperature (outlet water temperature or inlet water temperature), and determines that the water has reached an overboiling state if the water temperature is greater than the threshold value.

[0034] <Heater control in overboiling state> The control of the heater 11 in the overboiling state will be described below with reference to the flow chart shown in FIG. 6. The control unit of the heater control device 13 performs the following processes shown in S10 to S24. First, a predetermined pulse voltage is applied (implanted) from the power supply device to the heater circuit, and the current flowing through the heater 11 is acquired by the current detection unit (S10). Here, the voltage is applied for only a very short time, so the temperature rise of the heater 11 is very small, and the resistance value of the heater 11 does not fluctuate greatly. Next, the voltage detection unit acquires the voltage value applied to the heater 11 (S11). The resistance value of the heater 11 is calculated from the acquired current value and voltage value (S12).

[0035] The control unit acquires the outlet water temperature (S13), the inlet water temperature (S14), and the flow rate (S15). Here, the control unit may acquire only either the outlet water temperature or the inlet water temperature as the water temperature. For example, the control unit may acquire only the outlet water temperature, and estimate the inlet water temperature based on the acquired outlet water temperature, the amount of heat given to the water by the heater 11, the flow rate, etc.

[0036] The upper limit of power P is calculated according to the following formula (1): M is calculated (S16). M refers to the amount of heat required to raise the temperature of the amount of water flowing into the flow path 15 of the heating device 10 per second to the target temperature. In formula (1), M indicates the weight of water flowing into the flow path 15 of the heating device 10 per second (i.e., the mass flow rate), c indicates the specific heat of water, and dT indicates the temperature difference obtained by subtracting the inlet water temperature from the target temperature. Note that when the heating device 10 is in a normal use state, the flow rate is determined by the performance of the pump, etc., and is assumed to be a predetermined fixed value. Therefore, the process of acquiring the flow rate in S15 may be omitted, and this fixed value may be used as the numerical value of M.

number

[0037] The upper limit V of the voltage applied to the heater 11 is determined according to the following formula (2): Mis calculated (S17). R is the resistance value of the heater 11 obtained in S12. The upper limit value of the voltage V M is a quantity that varies with the inlet temperature.

number

[0038] Next, a PID control voltage value, which is a voltage value applied to the heater 11 in the PID control, is calculated (S18), and this PID control voltage value is set to the upper limit value V M It is determined whether the PID control voltage value is equal to or lower than the upper limit value V M If the PID control voltage value is equal to or lower than the upper limit value V (S19: Yes), the PID control voltage value is adopted as the set value of the voltage applied to the heater 11 (S20). M If it is greater than (S19: No), the upper limit of the voltage V M is adopted as the set value of the voltage applied to the heater 11 (S21).

[0039] A duty ratio for performing PWM control is calculated (S22) so that a set voltage is applied to the heater 11. An FET control signal is output based on the obtained duty ratio (S23). That is, a set voltage is applied to the heater 11 by PWM control.

[0040] The current detection unit again obtains the value of the current flowing through the heater 11 (S24), and after a predetermined time has elapsed, the processes from S11 onwards are repeated. The time required to move from S24 to S11 may be, for example, 10 milliseconds.

[0041] <Effects of the First Embodiment> As described above, the heater control device 13 of embodiment 1 is a heater control device 13 that monitors the temperature of the liquid (water) flowing through the flow path 15 and controls the heater 11 that is placed in the flow path 15 and heats the liquid to a target temperature.When the heater 11 is being controlled to raise the temperature of the liquid, and it is determined that the liquid has reached an overboiling state in which excessive evaporation of the liquid occurs at the interface between the heater 11 and the liquid, the output (power) of the heater 11 is reduced to the extent that the temperature of the liquid can be raised.

[0042] With this configuration, it is possible to efficiently raise the temperature of the liquid while suppressing excessive evaporation of the liquid at the interface between the heater 11 and the liquid.

[0043] In the first embodiment, the current value and voltage value of the heater 11 can be acquired, and when it is determined that the liquid has reached the overboiling state, the upper limit P of the output of the heater 11 is set according to the temperature of the liquid. M Set.

[0044] According to this configuration, the upper limit P of the output of the heater 11 is controlled according to the temperature of the liquid. M By setting the above, it is possible to efficiently raise the temperature of the liquid while further suppressing excessive evaporation of the liquid.

[0045] In the first embodiment, the flow rate of the liquid flowing through the flow path 15 can be obtained, and the upper limit P of the output of the heater 11 is set in consideration of the flow rate. M Set.

[0046] With this configuration, the upper limit value P of the output of the heater 11 can be set more accurately. M can be set.

[0047] In the first embodiment, the heater 11 is a ceramic heater.

[0048] According to this configuration, by suppressing the output of the ceramic heater in an overboiling state, it is possible to prevent the overheated ceramic heater from coming into contact with the liquid and being damaged.

[0049] The heating device 10 of the first embodiment includes a flow path 15 through which a liquid flows, a heater 11 disposed in the flow path 15, a thermometer 12 that measures the temperature of the liquid, and a heater control device 13.

[0050] With this configuration, it is possible to provide the heating device 10 that can efficiently heat the liquid.

[0051] [Details of the second embodiment of the present disclosure] A second embodiment of the present disclosure will be described with reference to Figures 7 and 8. Hereinafter, the description of the same configuration, action, and effect as those of the first embodiment may be omitted. In this embodiment, the heater control device 113 is capable of acquiring the resistance value of the heater 11, and detects the overboiling state based on the resistance value of the heater 11.

[0052] As described in the first embodiment, in the overboiling state, the portion of the heater 11 to which the air bubbles are attached cannot transfer heat to the water, and is therefore overheated. In addition, when the air bubbles leave the surface of the heater 11, the heat is transferred from the surface of the heater 11 to the water, and the temperature of that portion of the heater 11 drops. In this way, in the overboiling state, the generation of air bubbles and the detachment of the air bubbles from the surface of the heater 11 are repeated, causing the temperature of the heater 11 to rise or fall significantly locally. In general, the heating resistor of the heater 11 shows a tendency for the resistance value to increase with an increase in temperature. For this reason, in the overboiling state, a jump in the resistance value of the heater 11 that rises extremely is observed (see FIG. 7). In this embodiment, when the jump in the resistance value of the heater 11 exceeds a predetermined threshold value in the overboiling region, the control unit of the heater control device 113 determines that the overboiling state has been reached.

[0053] The control of the heater 11 in the second embodiment will be described with reference to the flow chart shown in FIG. 8. The control unit of the heater control device 113 performs the following processes shown in S30 to S39. The acquisition of the outlet water temperature (S30) and the acquisition of the inlet water temperature (S31) are the same as in the first embodiment. The resistance value of the heater 11 is measured a predetermined number of times, two or more (for example, five times), and the average value of the resistance value of the heater 11 is calculated (S32). Here, the resistance value of the heater 11 is calculated based on the current value measured by the current detection unit and the voltage value measured by the voltage detection unit when the pulse voltage or the control voltage used for heater control is applied, as in the first embodiment. Next, the latest value (an example of the current value) of the resistance value of the heater 11 is measured (S33). The calculation of the PID control voltage value (S34) is the same as in the first embodiment.

[0054] Next, the control unit judges whether or not the difference between the latest resistance value and the average resistance value of the heater 11 (the latest resistance value minus the average resistance value) is less than a predetermined threshold value (an example of a predetermined value) that is set in advance (S35). This predetermined threshold value is set in advance based on data of actual resistance value measurements in an overboiling state, etc. If the difference between the latest resistance value and the average resistance value is equal to or greater than the predetermined threshold value (S35: No), it is judged that the overboiling state has been reached, and a correction value of the PID control voltage value is increased by a predetermined increment (for example, 10 V). Here, the correction value is subtracted from the PID control voltage value calculated in S34, and the predetermined increment is set to a value that suppresses the generation and growth of bubbles in an overboiling state from becoming more active. The set value of the voltage applied to the heater 11 is the PID control voltage value minus the correction value (S37). If the difference between the latest value and the average value is less than a predetermined threshold value (S35: Yes), it is determined that the over-boiling state has not been reached, the correction value is not added, and the PID control voltage value is adopted as the setting value of the voltage applied to the heater 11 (S37).

[0055] The calculation of the duty ratio when performing PWM control (S38) and the output of the FET control signal (S39) are the same as in the first embodiment. After a predetermined time has elapsed, the processes from S30 onwards are repeated. The time from S39 to S30 can be, for example, 10 milliseconds. The correction value subtracted from the PID control voltage value in S37 is carried over from the correction value of the previous flow each time the flow is repeated. The correction value is reset when the power of the heating device 10 is turned off.

[0056] <Effects of the second embodiment> In the second embodiment, the resistance value of the heater 11 can be obtained, and the average and current resistance values ​​are obtained. When the difference between the average and current values ​​is equal to or greater than a predetermined value, it is determined that the overboiling state has been reached.

[0057] With this configuration, it is possible to determine whether the overboiling state has been reached based on the magnitude of the difference between the average resistance value of the heater 11 and the current resistance value.

[0058] <Other embodiments> (1) In the first embodiment, the heater 11 is a ceramic heater, but the heater may be a sheath heater or a PTC heater.

[0059] (2) In the first embodiment, the thermometer 5 for measuring the inlet water temperature is provided in the circulation circuit 2 outside the heating device 10. However, the thermometer for measuring the inlet water temperature may be provided in the flow path of the heating device.

[0060] (3) In the first embodiment, the heater 11 is cylindrical, but the shape of the heater can be changed as appropriate. [Explanation of symbols]

[0061] 1: Vehicle interior heating device, 2: Circulation circuit, 3: Heat exchanger, 4: Flow meter, 5: Thermometer, 6: Blower 10: heating device, 11: heater, 11A: first space, 12: thermometer, 13, 113: heater control device, 14: housing, 14A: second space, 14B: thermometer holder, 14C: substrate housing, 15: flow path, 15A: inlet, 15B: outlet A1: Area where air bubbles are attached to the surface of the heater P M : Upper limit of power (output), M: Mass flow rate of water, c: Specific heat of water, dT: Temperature difference obtained by subtracting the inlet water temperature from the target temperature, V M : Upper limit of voltage, R: Heater resistance

Claims

1. A heater control device that monitors a temperature of a liquid flowing through a flow path and controls a heater that is disposed in the flow path and heats the liquid to a target temperature, A heater control device that, when controlling the heater to raise the temperature of the liquid, determines that the liquid has reached an overboiling state in which excessive vaporization occurs at the interface between the heater and the liquid, reduces the output of the heater to the extent that the temperature of the liquid can be raised.

2. The current value and the voltage value of the heater can be acquired, The heater control device according to claim 1 , further comprising: a controller configured to set an upper limit of the output of the heater in accordance with the temperature of the liquid when it is determined that the liquid has reached the overboiling state.

3. A flow rate of the liquid flowing through the flow path can be obtained, The heater control device according to claim 2 , wherein the upper limit of the output of the heater is set in consideration of the flow rate.

4. A resistance value of the heater can be acquired, 2. The heater control device according to claim 1, wherein an average value and a current value of the resistance are obtained, and when a difference between the average value and the current value becomes equal to or greater than a predetermined value, it is determined that the over-boiling state has been reached.

5. The heater control device according to claim 1 , wherein the heater is a ceramic heater.

6. A flow path through which a liquid flows; A heater disposed within the flow path; a thermometer for measuring the temperature of the liquid; A heating device comprising: the heater control device according to any one of claims 1 to 5.

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