Heat medium heating device for vehicle

Abstract

To improve a PWM signal for controlling a heater, to reduce noise generated from the heater caused by the PWM signal, and to suppress breakage of a switching element, in a heat medium heating device for a vehicle.SOLUTION: A vehicle heat medium heating device 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 of a basic frequency lower than a predetermined range, and controls a current flowing through the heater based on the signal wave of the basic frequency. The signal wave is formed by repeating a period in which a duty ratio of a predetermined PWM signal is more than 0% and less than 100%, a period in which the duty ratio is 100%, a period in which the duty ratio is more than 0% and less than 100%, and a period in which the duty ratio is 0% in this order, and a switching frequency of the PWM signal is higher than a predetermined range.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Conventionally, electric vehicles and the like use 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 a 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 that includes a heater that generates heat when energized to heat the heat medium, a switching element provided in a current-carrying 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 it to the driver to control current to the heater. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-107067 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional heater control uses a PWM signal in the audio frequency range, which creates high-frequency noise when the square wave that makes up the PWM signal is switched on and off, resulting in noise from the heater. This is a particularly serious problem 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 audible frequency band as a PWM signal for a long period of time could cause the switching element to heat up, potentially resulting in malfunction or damage.

[0005] The present invention has been proposed to address these problems, namely, 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. [Means for solving the problem]

[0006] In order to solve the above problems, a vehicle heat medium heating device according to the present invention has the following configuration. 1. A vehicle heat medium heating device comprising: a heater for electrically heating a heat medium; and a control unit for controlling 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, wherein the signal wave is composed of a predetermined PWM signal, which is repeated in the order of a period in which the duty ratio is greater than 0% and less than 100%, a period in which the duty ratio is 100%, a period in which the duty ratio is greater than 0% and less than 100%, and a period in which the duty ratio is 0%, and wherein the switching frequency of the PWM signal is higher than the predetermined range. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is an external view of the heat medium heating device for a vehicle. [Figure 2] FIG. 2 is a cross-sectional view of the vehicle heat medium heating device. [Figure 3] FIG. 2 is a circuit diagram of a heat medium heating device for a vehicle. [Figure 4] An example of a PWM signal waveform. [Figure 5] An enlarged view of the rising edge of the PWM signal waveform in Figure 4. [Figure 6] FIG. 2 is a block diagram showing a schematic configuration of a control system of the apparatus according to the embodiment. [Figure 7] 10 shows a change over time in the duty ratio of a PWM signal according to the second embodiment (when the target duty ratio is 40%). [Figure 8] 10 shows a change over time in the duty ratio of a PWM signal according to the second embodiment (when the target duty ratio is 120%). [Figure 9] 10 shows a general relationship between the waveforms of PWM signals for each heater according to the second embodiment. [Figure 10] 10 shows the relationship between the waveforms of PWM signals for each heater according to the second embodiment (when the target duty ratio is less than 100%). [Figure 11] 10 shows a change over time in the duty ratio of a PWM signal according to the third embodiment (when the target duty ratio is 40%). [Figure 12] 10 shows a change over time in the duty ratio of a PWM signal according to the third embodiment (when the target duty ratio is 120%). DETAILED DESCRIPTION OF THE INVENTION

[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 sends to the switching element to heat the heater is sometimes called the "heater duty ratio" or the "duty ratio generated by the switching element." Also, the "audible frequency band" refers to the human audible frequency range, which is between 20 Hz and 20 kHz, depending on the conditions.

[0011] 1 and 2, the 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 circulate 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 inside the housing 3. A rectangular parallelepiped storage space is formed in the housing 3 to store the heaters 2 (2A, 2B), and when the heaters 2 (2A, 2B) are stored 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 portion 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 another 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 multiple 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 or more elements are 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 also 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 square 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 square wave are composed of square waves having a frequency exceeding the audible frequency. These PWM signals are generated by a control unit housed in a circuit component within circuit component housing 30 provided in 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 more than 0% and less than 100%, for example, a constant value. However, for example, as shown in FIG. 5, gradually increasing the duty ratio from 0% to 10% increments 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 more 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, as shown in FIG. 4, 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.

[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, and if the number 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, and 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 between less than 100% and 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 current value changes continuously over time.

[0028] The second period length and the fourth period length do not need to be the same, and are determined taking into consideration the power-on time required to heat the heater and the suppression of heat generation by the switching element. The first period to the fourth period constitute one period 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 switching frequency square wave at the rising and falling edges of the pseudo fundamental frequency square wave 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 preventing EMC noise. Furthermore, since it is not necessary to introduce additional components such as filters for reducing noise, it is possible to reduce the number of components, costs, and power consumption.

[0033] (Second embodiment) Next, a second embodiment of 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 portion 30 provided in the housing 3.

[0034] The second embodiment uses multiple heaters, which makes it possible to operate the heaters for a long 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 range, and also makes it possible to prevent the smoothing capacitor constituting the noise filter 8 from becoming large in capacity.

[0035] The configuration of the control system of the device according to the second embodiment is as shown in FIG. 6, and the PWM signal waveform is formed by the control unit 7 based on the target duty ratio calculated by the target duty ratio calculation unit 40. The target duty ratio is a preset value, and refers to 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 the 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 known calculation means provided in the circuit components of the vehicle. Then, the switching element 5 energizes the heater 2 in accordance with a PWM signal from the control unit 7, thereby adjusting the temperature of the heater 2.

[0036] Below, control when there are two heaters 2 (2A, 2B) will be described from the perspective of the relationship between the duty ratio and time. The control unit 7 repeatedly performs steady-state control, which controls the duty ratio to be constant, and switching control, which changes the duty ratio.

[0037] FIG. 7 shows the case where the target duty ratio is 40%, and 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%, followed by steady-state control to maintain the duty ratio at a constant 40%. After that, switching control is performed to decrease the duty ratio from 40% to 0%, followed by 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 it is preferable that one cycle be below the audible frequency, as in the first embodiment. It is also preferable that the time-series change in the duty ratio for each cycle be 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, it 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 that heaters 2A and 2B have a period during which they 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 total duty ratio of each heater 2 (2A, 2B) during the switching control period and keeping it constant, including during the steady-state control period, it is possible to keep the total value of the current flowing through the heaters 2 (2A, 2B) constant. In other words, the total duty ratio 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, by suppressing voltage fluctuations in the power supply connected to the heaters 2 (2A, 2B), it is possible to prevent the smoothing capacitor from becoming large. This effect is achieved even 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 is also true when the target duty ratio, which will be described later, is 100% or more.

[0040] Furthermore, there are no particular restrictions 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 ratio may be increased or decreased at a constant rate, or the duty ratios of heater 2A and heater 2B may each be set to 1 / 2 of the target duty ratio. However, from the viewpoint of improving NVH, it is more preferable to control the heaters 2 (2A, 2B) 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 in the steady control period when the duty ratio is large and over the switching control period, and so that the sum of the duty ratios of the heaters 2A and 2B matches the target duty ratio, which 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 element 5 (5A, 5B) is diminished, so it is preferably set to 100 cycles or less, more preferably 30 cycles or less, in terms of the square wave number of the PWM signal. Furthermore, the period during which the duty ratio of heater 2A is constant at 0% and the period during which the duty ratio of heater 2A is constant at 40% do not necessarily have to be equal, but it is preferable to make them equal and to make the frequencies of use of switching elements 5A and 5B the same 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 time during which no switching is performed is secured, 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% as the boundary. In either case, however, a period during which no switching is required (periods during which the duty ratio is 0% and 100%) can be secured, thereby preventing the switching element 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 these heaters (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 used, but two of these (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 way, each switching element 5 (5A to 5C) can have an equal non-switching period, which prevents the switching elements 5 (5A to 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, while the other heaters are rotated so that their duty cycles are either 0% or 100%. Rotating the heaters so that the switching periods are equal is particularly desirable in that it evens out damage to each switching element and extends 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 Figure 9(A), when the rising edges of the duty periods of heaters 2A and 2B coincide, ripples occur, requiring a larger 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 Figure 9(B).

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

[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 of 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 FIG. 10, the white triangles represent the spaced apart portions, showing an example in which the ON periods of heaters 2A and 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 FIG. 9(C).

[0051] From the perspective of reducing NVH, it is preferable to turn on the waveform of switching element 5A when the waveform of switching element 5 (for example, 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 change 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, multiple 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, one heater 2 is sufficient, and the switching elements 5A and 5B are driven alternately as shown in Fig. 11. In this way, it is possible to prevent the switching elements 5 (5A, 5B) from becoming too hot.

[0054] If the target duty ratio is 100% or higher, multiple heaters 2 are required. For example, if the target duty ratio is 120%, as shown in Fig. 12, switching elements 5A and 5B connected to heater 2A are alternately driven, and switching elements 5C and 5D connected to 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 have a repeating pattern of a period in which they are driven but not switching (period with a duty ratio of 100%), a period in which they are switching (period with a duty ratio of 20%), and a period in which they are not driven at all (period with a duty ratio of 0%), which enables heat dispersion and prevents the switching elements 5 (5A to 5D) from becoming too hot.

[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 heater 2A and the heater 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 are 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. [Explanation of symbols]

[0062] 1: Vehicle heating medium heating device, 2, 2A, 2B, 2C: Heater, 2T: Terminal section, 3: Housing, 3A: First housing part, 3B: Second housing part, 4: Sealing member, 5: 5A, 5B, 5C: switching elements, 6: power semiconductors, 7: control unit, 8: Noise filter, 10, 10A, 10B: heating flow path, 11: communication flow path, 13: inlet portion, 14: outlet portion, 20: Enlarged flow path portion, 30: Circuit component storage 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, The control unit A signal wave having a fundamental frequency lower than a predetermined range is generated, and a current flowing through the heater is controlled based on the signal wave having the fundamental frequency, The signal wave is The period is composed of a period in which the duty ratio of a predetermined PWM signal is greater than 0% and less than 100%, a period in which the duty ratio is 100%, a period in which the duty ratio is greater than 0% and less than 100%, and a period in which the duty ratio is 0%, The switching frequency of the PWM signal is higher than the predetermined range. A vehicle heat medium heating device comprising:

2. The predetermined range is the audio frequency range.

2. The vehicle heat medium heating device according to claim 1.

3. In the signal wave of the fundamental frequency, During a period in which the duty ratio is greater than 0% and less than 100%, the duty ratio of the switching frequency is gradually changed.

3. The vehicle heat medium heating device according to claim 1 or 2.

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