Heat medium heating device for vehicle

Abstract

[Problem] To address the problem of improving a PWM signal that controls a heater, reducing noise generated from the heater due to the PWM signal, and suppressing breakage of a switching element. [Solution] A heat medium heating device for a vehicle is provided with a heater for electrically heating a heat medium and a control unit for controlling the heater. The heat medium heating device for a vehicle is characterized in that: the control unit generates a signal wave with a fundamental frequency lower than a prescribed range and controls a current flowing in the heater, on the basis of the signal wave with the fundamental frequency; the signal wave is formed through repetition of the periods of the duty ratio of a prescribed PWM signal, in the following order of a period in which the duty ratio is greater than 0% to less than 100%, a period in which the duty ratio is 100%, a period in which the duty ratio is greater than 0% to less than 100%, and a period in which the duty ratio is 0%; and a switching frequency of the PWM signal is higher than a prescribed range.

Description

Vehicle heat transfer medium heating device

[0001] The present invention relates to a heat medium heating device for a vehicle.

[0002] In the past, electric vehicles and the like have used heat obtained from outside air using an external heat exchanger as a heat source for heating the interior of the vehicle. When heat absorption from the outside air is insufficient, a heater provided in the vehicle heat medium heating device is used to heat a heat medium (including water, coolant, refrigerant, etc.) for heating the interior of the vehicle to make up for the lack of thermal energy. For example, Patent Document 1 describes a vehicle heat medium heating device including a heater that generates heat when energized to heat the heat medium, a switching element provided in a current supply circuit to the heater and capable of turning current on and off, a driver that drives the switching element on and off, and a control unit that generates a PWM signal based on a heating request and outputs the PWM signal to the driver to control current supply to the heater.

[0003] Japanese Patent Application Laid-Open No. 2023-107067

[0004] However, conventional heater control using a PWM signal in the audio frequency range has posed a problem of noise from the heater due to high-frequency noise generated when the square wave constituting the PWM signal is switched on and off. This problem is particularly serious when a coiled heating wire is used for the heater. This problem has become even more pronounced with the recent spread of electric vehicles. Furthermore, simply using a signal wave exceeding the audio frequency range as a PWM signal for a long period of time can cause the switching element to overheat, potentially resulting in malfunction or damage.

[0005] The present invention has been proposed to address these problems, and aims to improve the PWM signal that controls the heater, reduce the noise generated by the heater due to the PWM signal, and prevent damage to the switching element.

[0006] In order to solve the above problems, a heat medium heating device for a vehicle according to the present invention has the following configuration: The heat medium heating device for a vehicle includes a heater that electrically heats a heat medium and a control unit that controls the heater, wherein the control unit generates a signal wave having a fundamental frequency lower than a predetermined range and controls a current flowing through the heater based on the signal wave of the fundamental frequency, the signal wave being composed of a predetermined PWM signal that is repeatedly configured, in order, with a duty ratio of more than 0% but less than 100%, a duty ratio of 100%, a duty ratio of more than 0% but less than 100%, and a duty ratio of 0%, and the switching frequency of the PWM signal is higher than the predetermined range.

[0007] According to the present invention having such characteristics, by improving the PWM signal that controls the heater, it is possible to reduce noise generated from the heater due to the PWM signal and to suppress damage to the switching element.

[0008] 5 is an external view of a heat medium heating device for a vehicle; a cross-sectional view of a heat medium heating device for a vehicle; a circuit diagram of a heat medium heating device for a vehicle; an example of a waveform of a PWM signal; an enlarged view of a rising portion of the waveform of the PWM signal in FIG. 4; a block diagram showing a schematic configuration of a control system of a device according to an embodiment; a time change in the duty ratio of a PWM signal according to a second embodiment (when the target duty ratio is 40%); a time change in the duty ratio of a PWM signal according to a second embodiment (when the target duty ratio is 120%); a relationship (general) of the waveform of a PWM signal with respect to each heater according to the second embodiment; a relationship (when the target duty ratio is less than 100%) of the waveform of a PWM signal with respect to each heater according to the second embodiment (when the target duty ratio is 40%); a time change in the duty ratio of a PWM signal according to a third embodiment (when the target duty ratio is 120%).

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Each drawing shows one embodiment of the present invention and is not intended to limit the present invention. In the following description, the same reference numerals in different drawings indicate parts with the same function, and duplicate explanations in each drawing will be omitted as appropriate. Furthermore, the dimensional relationships between elements in the drawings are for ease of understanding and are not intended to limit the actual dimensional ratios.

[0010] The duty ratio of the PWM signal that the control unit issues to the switching element to heat the heater is sometimes called the "heater duty ratio" or the "duty ratio generated by the switching element." The "audible frequency band" refers to the human audible frequency band, which is between 20 Hz and 20 kHz, depending on the conditions.

[0011] 1 and 2, a vehicle heat medium heating device 1 includes a plurality of heaters 2 (2A, 2B) and a housing 3. In a first embodiment described later, the heater 2 (2A, 2B) may be a single heater.

[0012] The heaters 2 (2A, 2B) are housed in a housing 3, and heating flow paths 10 (10A, 10B) that allow a heat medium to flow along the heaters 2 (2A, 2B) are formed around the heaters 2 (2A, 2B) in the housing 3. The housing 3 also has a communication flow path 11 that connects the heating flow paths 10 (10A, 10B).

[0013] The heaters 2 (2A, 2B) have terminals 2T on one end thereof, which are connected to a control board (not shown) via connecting wiring (bus bars). Both ends of the heaters 2 (2A, 2B) are supported within the housing 3 via sealing members 4 (e.g., O-rings).

[0014] The heaters 2 (2A, 2B) are arranged in parallel within the housing 3. A rectangular parallelepiped storage space is formed in the housing 3 to house the heaters 2 (2A, 2B), and with the heaters 2 (2A, 2B) housed in this storage space, gaps formed around the heaters 2 (2A, 2B) become heating flow paths 10 (10A, 10B) for the heat medium.

[0015] In the illustrated example, the housing 3 is provided with an inlet 13 and an outlet 14 for the heat medium on the opposite side of the terminal 2T of the heater 2 (2A, 2B). The inlet 13 is connected to a heating flow path 10 (10A) that houses one heater 2 (2A), and the outlet 14 is connected to a heating flow path 10 (10B) that houses the other heater 2 (2B). The heat medium that flows in from the inlet 13 of the housing 3 is heated while passing through one heating flow path 10 (10A) that houses the heater 2 (2A), flows through the communicating flow path 11, and is further heated while passing through the other heating flow path 10 (10B) that houses the heater 2 (2B), before reaching the outlet 14.

[0016] A circuit component accommodating section 30 is formed between the plurality of heating flow paths 10 (10A, 10B) arranged in parallel in the housing 3. The circuit component accommodating section 30 accommodates circuit components and the like that are connected to a control board (not shown).

[0017] The housing 3 includes a first housing portion 3A and a second housing portion 3B. The first housing portion 3A is formed with the above-mentioned multiple heating flow paths 10 (10A, 10B) and the communicating flow path 11, as well as with an inlet portion 13 and an outlet portion 14, and is further provided with a circuit component accommodating portion 30. In contrast, the second housing portion 3B is formed with a flow path enlargement portion 20 that enlarges the flow path of the communicating flow path 11.

[0018] Next, a description will be given of the main circuit configuration of the vehicle heat medium heating device 1. As shown in Fig. 3, the vehicle heat medium heating device 1 includes switching elements 5 (5A to 5C), heaters 2 (2A to 2C), a power semiconductor 6, and a noise filter 8. Note that Fig. 3 shows an example in which three switching elements 5 (5A to 5C) and three heaters 2 (2A to 2C) are provided, but at least one element is sufficient, and four or more elements may be provided.

[0019] The switching elements 5 (5A to 5C) are, for example, IGBTs (insulated gate bipolar transistors). By PWM controlling the switching elements 5 (5A to 5C), the duty ratio of current supplied to the heaters 2 (2A to 2C) is adjusted, and the temperatures of the heaters 2 (2A to 2C) are adjusted.

[0020] The switching elements 5 (5A to 5C), heaters 2 (2A to 2C), and power semiconductors 6 are connected in series, with the switching elements 5 (5A to 5C) disposed on the positive side HV+ of the high-voltage power supply and the power semiconductors 6 disposed on the negative side HV- of the high-voltage power supply. The switching elements 5 (5A to 5C) are disposed in parallel with each other. A noise filter 8 is disposed between the high-voltage power supplies in parallel with the switching elements 5 (5A to 5C), heaters 2 (2A to 2C), and power semiconductors 6.

[0021] First Embodiment Next, a first embodiment relating to heater control using a PWM signal will be described with reference to Fig. 4. The invention according to the first embodiment is also applicable to a case where there is only one heater.

[0022] Specifically, a PWM signal having a switching frequency exceeding the audible frequency band is used to generate a pseudo rectangular wave signal having a frequency below the audible frequency (hereinafter sometimes referred to as the "fundamental frequency"), and the rising and falling edges of this rectangular wave are formed by rectangular waves having a frequency exceeding the audible frequency. The generation of these PWM signals is performed by a control unit housed in a circuit component within the circuit component housing 30 provided in the housing 3.

[0023] FIG. 4 shows an example in which a fundamental frequency below the audible frequency is a square wave of 10 Hz, and a switching frequency above the audible frequency is a square wave of 25 kHz.

[0024] The square wave of the fundamental frequency is formed by changing the duty ratio of the square wave of the switching frequency, and is divided into the following four periods depending on the duty ratio of the switching frequency. The first period is the period when the duty ratio of the switching frequency is greater than 0% and less than 100%. The second period is the period when the duty ratio is 100%. The third period is the period when the duty ratio is less than 100% and greater than 0%. Finally, the fourth period is the period when the duty ratio is 0%.

[0025] The duty ratio during the first period may be any value between greater than 0% and less than 100%, for example, a constant value. However, for example, gradually increasing the duty ratio from 0% to 10% as shown in FIG. 5 is preferable in terms of smoothly changing the current value. In particular, it is particularly preferable to increase the duty ratio during the first period from greater than 0% to less than 100% over time so that the change in the current value over time from the first period to the second period is continuous. Note that "continuous" here means, for example, that the change in the current value over time during the first period (curve A in FIG. 4) increases monotonically and the derivative of the function representing the change in the current value over time between the first and second periods is continuous, as shown in FIG. 4.

[0026] The first period is composed of square waves with a switching frequency of 4 to 100, preferably 7 to 30. If the number of square waves is too small, the noise reduction effect will be poor, while if the number of square waves is too large, the number of switching operations will increase, which will result in overheating of the switching elements. Furthermore, as shown in Figure 4, it is preferable that the integrated values ​​of the current values ​​(shown by curve A) for the first and third periods are the same. For example, it is preferable that the first and third periods are the same.

[0027] The duty ratio of the third period may be any value from less than 100% to more than 0%, for example, it may be a constant value. However, as described above, it is preferable to gradually decrease the duty ratio of the third period from less than 100% to more than 0% over time so that the change in the current value over time is continuous.

[0028] The lengths of the second and fourth periods do not need to be the same, and are determined taking into account the power supply time required to heat the heater and the need to suppress heat generation by the switching element. The first to fourth periods constitute one cycle of the fundamental frequency.

[0029] Thus, according to the first embodiment, a pseudo-rectangular wave of a frequency lower than the audible frequency is generated from a PWM signal exceeding the audible frequency band as the rectangular wave used for PWM control, and the rising and falling portions of the pseudo-rectangular wave are used to control the heater, thereby making it possible to suppress noise generated by the heater while using PWM control.

[0030] Furthermore, since the switching element has an OFF period with a duty ratio of 0% and an ON period of 100% every 10 Hz, the number of switching operations can be reduced, and heat generation in the switching element can be suppressed.

[0031] Furthermore, when the duty ratio of the square wave of the switching frequency at the rising and falling edges of the square wave of the pseudo fundamental frequency is gradually changed, the peak current can be reduced compared to when the duty ratio is constant, which makes it possible to further suppress noise and improve NVH (Noise Vibration Harshness).

[0032] This method is also effective in reducing EMC noise. In addition, since it is not necessary to introduce additional components such as filters to reduce noise, it is possible to reduce the number of components, costs, and power consumption.

[0033] Second Embodiment Next, a second embodiment relating to heater control using a PWM signal will be described. Note that the PWM signal control in the second embodiment is performed by a control unit housed in a circuit component housed in a circuit component housing 30 provided in the housing 3.

[0034] The second embodiment uses multiple heaters, which makes it possible to operate the heaters for a long period of time while suppressing noise, without causing malfunction or damage due to high temperatures of the switching elements, even if the switching frequency exceeds the audible frequency band, and also makes it possible to prevent the smoothing capacitor constituting the noise filter 8 from becoming large in capacity.

[0035] The control system configuration of the device according to the second embodiment is as shown in FIG. 6 , and the PWM signal waveform is generated by the control unit 7 based on a target duty ratio calculated by a target duty ratio calculation unit 40. The target duty ratio is a preset value, e.g., the duty ratio generated by the switching element 5 to energize the heater 2, calculated based on peripheral information 42 such as the interior temperature so as to achieve a vehicle interior temperature setting 41 set by the occupant. When there are multiple heaters 2, the target duty ratio refers to the sum of the duty ratios of the heaters 2 to be set. In other words, when there are two heaters 2 (2A, 2B), the target duty ratio is in the range of 0 to 200%. The duty ratio is calculated by a known calculation means provided in the vehicle's circuit components. The switching element 5 energizes the heater 2 in accordance with the PWM signal from the control unit 7, thereby adjusting the temperature of the heater 2.

[0036] The following describes the control when there are two heaters 2 (2A, 2B) in terms of the relationship between the duty ratio and time. The control unit 7 repeatedly performs steady-state control to keep the duty ratio constant and switching control to change the duty ratio.

[0037] FIG. 7 shows the case where the target duty ratio is 40%, in which the control unit 7 performs switching control to increase the duty ratio of the heater 2A from 0% to the target duty ratio of 40%, and then performs steady-state control to maintain the duty ratio at a constant 40%. Subsequently, switching control is performed to decrease the duty ratio from 40% to 0%, and then performs steady-state control to maintain the duty ratio at a constant 0%. Note that the horizontal axis in FIG. 7 represents time, and the vertical axis represents the duty ratio. The period during which the duty ratio remains constant is sometimes referred to as the steady-state control period, and the period during which the duty ratio changes is sometimes referred to as the switching control period. The period from one increase in the duty ratio to the next increase corresponds to one cycle, and, as in the first embodiment, one cycle is preferably below the audible frequency. The time-series change in the duty ratio for each cycle is preferably the same as in the first embodiment.

[0038] The control unit 7 performs switching control to reduce the duty ratio of heater 2B from the target duty ratio of 40% to 0% in accordance with the control of heater 2A, and then performs steady-state control to maintain the duty ratio at a constant 0%. Thereafter, the control unit 7 performs switching control to increase the duty ratio from 0% to the target duty ratio of 40%, and then performs steady-state control to maintain the constant 40% state. This ensures a period during which heaters 2A and 2B are not driven or switched (a period during which the duty ratio is 0%), thereby suppressing heat generation from the switching elements 5 (5A, 5B).

[0039] Furthermore, by aligning the sum of the duty ratios of the heaters 2 (2A, 2B) during the switching control period and maintaining it constant, including during the steady-state control period, the total value of the current flowing through the heaters 2 (2A, 2B) can be maintained constant. That is, the sum of the duty ratios generated by the switching elements 5 (5A, 5B) is controlled to be the set target duty ratio throughout the entire period. As a result, fluctuations in the current value can be reduced, thereby reducing NVH. Furthermore, voltage fluctuations in the power supply connected to the heaters 2 (2A, 2B) can be suppressed, thereby preventing the need for a large smoothing capacitor. These effects are also achieved when the duty ratio of one of the heaters 2 (2A, 2B) is not necessarily set to 0%. This effect is common to the second embodiment and applies equally to cases where the target duty ratio, described below, is 100% or greater.

[0040] Furthermore, there are no particular limitations on the rate of change of the duty ratio for each heater 2 (2A, 2B) during switching control. For example, as shown in FIG. 7, the duty ratios may be increased or decreased at a constant rate, or the duty ratios of heaters 2A and 2B may each be set to half the target duty ratio. However, from the perspective of improving NVH, it is more preferable to control the duty ratios so that the differential value of the function representing the time change in the current value of each heater 2 (2A, 2B) is continuous at least over the period of the steady-state control period when the duty ratio is large and over the switching control period, and so that the sum of the duty ratios of heaters 2A and 2B matches the target duty ratio. This is basically the same as in the first embodiment.

[0041] Furthermore, if the switching control period is too long, the effect of reducing the number of switching times of the switching elements 5 (5A, 5B) will be diminished, so it is preferably set to 100 cycles or less in terms of the square wave number of the PWM signal, and more preferably 30 cycles or less. Furthermore, the period during which the duty ratio of the heater 2A is constant at 0% and the period during which the duty ratio of the heater 2A is constant at 40% do not necessarily have to be equal, but making them equal and aligning the usage frequencies of the switching elements 5A and 5B is preferable in terms of the lifespan of the switching elements.

[0042] Next, the case where the target duty ratio is 120% will be described, focusing on the differences from the case where the duty ratio is 40%. As shown in FIG. 8 , the control unit 7 first sets the duty ratio of heater 2A to a constant 100% and the duty ratio of heater 2B to a constant 20%. In this case, heater 2A is always driven, but because the duty ratio is set to 100%, a period of no switching is ensured, thereby suppressing heat generation from switching element 5A. Thereafter, the control unit 7 switches the duty ratio of heater 2A to a constant 20% and the duty ratio of heater 2B to a constant 100%. Therefore, for the same reason, heat generation from switching element 5B, which controls heater 2B, can be suppressed.

[0043] In this way, when there are two heaters 2 (2A, 2B), the duty ratio of one steady-state control period will be either 0% or 100%, with the target duty ratio of 100% being the boundary. In either case, however, a period during which no switching is required (a period during which the duty ratio is 0% and a period during which the duty ratio is 100%) can be secured, thereby preventing the switching elements 5 (5A, 5B) from becoming too hot.

[0044] When there are three heaters 2 (2A-2C), the process is basically the same as when there are two heaters 2 (2A, 2B). When the target duty ratio is less than 100%, only one heater 2 (e.g., 2A) is used simultaneously, and the duty ratios of the other two heaters are controlled to 0%. Then, in the next cycle, the heater 2A that was used is rested (its duty ratio is set to 0%). When the target duty ratio is 100% or more but less than 200%, only two heaters 2 (e.g., 2A, 2B) are used simultaneously, and the duty ratio of one of them (e.g., 2A) is always set to 100%, so that only one switching element (5B) is switched on. Then, in the next cycle, for example, the switched switching element 5B is rested, and the duty ratio of the rested heater (2C) is set to 100%. Furthermore, when the target duty ratio is 200% or higher, three heaters 2 are always in use, but two of these heaters (2A, 2B) are controlled to always have a duty ratio of 100%, and only one switching element (5C) is controlled for switching. Then, in the next cycle, the switched switching element 5C is controlled to be used at 100%. By controlling in this manner, each switching element 5 (5A-5C) can have an equal non-switching period, which prevents the switching elements 5 (5A-5C) from overheating and extends their lifespan. The same applies when there are four or more heaters 2.

[0045] That is, when there are multiple heaters, only one heater is switched on and off, and the other heaters are rotated so that their duty ratios are either 0% or 100%. Rotating the heaters so that the switching periods are equal is particularly preferable in terms of balancing damage to each switching element and extending the life of the entire circuit. By providing periods of non-switching in this way, it is possible to reduce NVH and suppress heat generation from the switching elements.

[0046] Next, the switching control period will be described in detail.

[0047] As shown by the black triangles in Fig. 9A, when the rising edges of the duty periods of heaters 2A and 2B coincide, ripples occur, requiring a larger capacity smoothing capacitor. The same is true when the falling edges of the duty periods of heaters 2A and 2B coincide, as shown by the black triangles in Fig. 9B.

[0048] The black triangles in Fig. 9C represent the case where the fall of heater 2A coincides with the rise of heater 2B. In the case of Fig. 9C, for example, if the timing at which heater 2A is turned off is advanced, an OFF period in which no current flows can be provided between the timing at which heater 2A is turned on and the timing at which heater 2B is turned on, which is effective in preventing the smoothing capacitor from becoming large in capacity.

[0049] In this way, the control unit controls the ON period of the PWM signal of each heater so as to shift the timing at which at least two or more heaters among the multiple heaters are turned ON (FIG. 9(A)) or OFF (FIG. 9(B)) during the switching control period, in accordance with the three patterns shown in FIGS. 9(A) to 9(C), or to shift the timing at which one heater is turned OFF (FIG. 9(C)) from the timing at which at least one of the other heaters is turned ON.

[0050] In particular, when the target duty ratio is less than 100%, the control unit controls the switching elements 5 (5A, 5B) so that the ON periods during which current is supplied to each heater 2 (2A, 2B) are spaced apart. For example, in Figure 10, the white triangles represent the spaced apart portions, showing an example in which the ON periods of heater 2A and heater 2B are not continuous. By controlling in this way, the flowing current can be subdivided, making it possible to suppress an increase in the capacity of the smoothing capacitor, as in the case of Figure 9(C).

[0051] From the viewpoint of reducing NVH, it is preferable to turn on the waveform of switching element 5A when the waveform of switching element 5 (e.g., 5B) turns off. This is because instantaneous on / off control keeps the current flowing through heater 2 (2A, 2B) at a constant value and minimizes the number of changing points in the flowing current. Here, the period during which the duties of switching elements 5B and 5A are continuously on corresponds to the period of the target duty ratio.

[0052] Third Embodiment In the first and second embodiments, one switching element 5 is connected to one heater 2. In the third embodiment, a plurality of switching elements 5 are connected to one heater 2. In the following, an example will be described in which switching elements 5 (5A, 5B) are connected to heater 2A and switching elements 5 (5C, 5D) are connected to heater 2B.

[0053] As an example of a case where the target duty ratio is less than 100%, a case where the target duty ratio is 40% will be described. In this case, only one heater 2 is required, and the switching elements 5A and 5B are alternately driven as shown in Figure 11. This makes it possible to prevent the switching elements 5 (5A, 5B) from becoming too hot.

[0054] If the target duty ratio is 100% or more, it is necessary to have a plurality of heaters 2. For example, if the target duty ratio is 120%, as shown in Fig. 12, the switching elements 5A and 5B connected to the heater 2A are alternately driven, and the switching elements 5C and 5D connected to the heater 2B are also alternately driven.

[0055] 12, for example, switching element 5A is driven at a duty ratio of 100%, then at a duty ratio of 20%, and then at 0%. Meanwhile, the duty ratio of switching element 5B increases from 0% to 100% when the duty ratio of switching element 5A decreases from 20% to 0%. Thereafter, switching element 5B is driven at a duty ratio of 100%, then at a duty ratio of 20%, and then at 0%.

[0056] In this way, the switching elements 5A and 5B adopt a repeating pattern in which they are driven but not switching (periods with a duty ratio of 100%), periods with switching (periods with a duty ratio of 20%), and periods with no driving at all (periods with a duty ratio of 0%), thereby enabling heat dispersion and preventing the switching elements 5 (5A to 5D) from overheating.

[0057] The switching elements 5C and 5D connected to the heater 2B are basically controlled in the same repeating pattern as the switching elements 5A and 5B, except that the sum of the duty ratios generated by all the switching elements 5 (5A to 5D) for the heaters 2A and 2B is set to a target duty ratio of 120%, for example, by setting the duty ratio of the switching element 5D to 20% when the duty ratio of the switching element 5A is 100%.

[0058] Furthermore, the repetition pattern for the switching elements 5 (5A to 5D) can be any pattern that can uniformly heat up each of the switching elements 5. For example, there is a pattern in which the duty ratio is set to 0%, then to 20%, then to 100%, and then to 0%, or a pattern in which the duty ratio is set to 0% → 100% → 20% → 100% → 20% → 0%.

[0059] It is preferable that the time-series changes in the duty ratio of the switching elements shown in FIGS. 11 and 12 be similar to those in the first embodiment.

[0060] 9 and 10 are also applied to the third embodiment. In this case, the "heater" in the description of FIGS. 9 and 10 should be read as the "switching element."

[0061] The embodiments of the present invention have been described above in detail with reference to the drawings, but the specific configuration is not limited to the described embodiments, and the present invention also includes design changes and the like within the scope of the gist of the present invention.

[0062] 1: Vehicle heat medium heating device, 2, 2A, 2B, 2C: heater, 2T: terminal portion, 3: housing, 3A: first housing portion, 3B: second housing portion, 4: sealing member, 5: 5A, 5B, 5C: switching element, 6: power semiconductor, 7: control portion, 8: noise filter, 10, 10A, 10B: heating flow path, 11: communication flow path, 13: inlet portion, 14: outlet portion, 20: flow path expansion portion, 30: circuit component accommodating portion

Claims

1. A vehicle heat medium heating device comprising a heater that electrically heats a heat medium and a control unit that controls the heater, wherein the control unit generates a signal wave with a fundamental frequency lower than a predetermined range and controls the current flowing to the heater based on the signal wave of the fundamental frequency, wherein the signal wave is composed of a repetition of a period in which the duty ratio of a predetermined PWM signal is greater than 0% and less than 100%, a period of 100%, a period of greater than 0% and less than 100%, and a period of 0% duty ratio, and wherein the switching frequency of the PWM signal is higher than the predetermined range.

2. The vehicle heating medium heating device according to claim 1, wherein the predetermined range is an audible frequency band.

3. The vehicle heat medium heating device according to claim 1 or 2, characterized in that, in the signal wave of the fundamental frequency, the duty ratio of the switching frequency is gradually changed during a period in which the duty ratio is greater than 0% and less than 100%.

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