JP2009153330A - Controller of electric fan - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller for an electric fan that reduces generation of vibration and noise even if the number of rotations is low. <P>SOLUTION: The controller for the electric fan has a section 13 for determining whether the actual number of rotations is more than a predetermined threshold number of rotations or under the threshold number of rotations, and a PWM signal is set at a first frequency f1 if the actual number of rotations is determined to be more than the threshold number of rotations by the section 13. The PWM signal is set at a second frequency f2 higher than the first frequency f1 if the actual number of rotations is under the threshold number of rotations. A PWM signal having a duty ratio dependent on the set frequency and the set number of rotations is generated and used for controlling an electronic switch. As a result, generation of noise can be reduced even if a low number of rotations is set. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an electric fan mounted on a vehicle, and more particularly to a technique for suppressing the occurrence of vibration and noise.

  For example, the rotational speed of an electric fan used for cooling a radiator mounted on a vehicle is controlled according to the water temperature of the radiator. The electric fan mounted on such a vehicle is switched on and off by an electronic switch such as a MOSFET provided between the battery and the electric fan. Furthermore, the rotational speed of the electric fan is controlled by driving the electronic switch by PWM control and adjusting the duty ratio of PWM.

  A conventional electric fan control device, for example, supplies a PWM signal having a frequency of about 20 [KHz] to a control terminal of an electronic switch, drives the electronic switch, and supplies desired electric power to the electric fan. Is controlled to have a predetermined rotation speed.

  Here, in the conventional PWM control, a relatively high frequency of about 20 [KHz] is often used as described above, and noise is generated when the electronic switch is driven by a high frequency PWM signal. There is a problem that the electronic switch and other driving devices need to have performance capable of supporting high frequencies, leading to an increase in cost.

Therefore, for example, in Japanese Patent Laid-Open No. 2002-142494 (Patent Document 1), by setting the frequency of PWM control to a low frequency of several tens of Hz or less, noise generated in the electronic switch is prevented, and heat generation and switching loss are performed. Is disclosed.
JP 2002-142494 A

  However, setting the PWM control frequency to a low frequency has the advantages of reducing noise, reducing heat generation, and switching loss. On the other hand, when the electric fan is driven at a low speed by reducing the duty ratio, Resonance occurs between the two. That is, since the resonance frequency of the vehicle is usually about several tens of Hz, resonance occurs between the vehicle and the body, which causes problems such as driving fatigue due to vibration and stress due to abnormal noise. This will be specifically described below.

  FIG. 7 is a characteristic diagram showing changes in the rotational speed of the electric fan when the electronic switch is driven by the PWM signal and the electric fan is rotated. FIG. 7A shows a case where the rotational speed is high ( For example, 500 [rpm]) and FIG. 7B show a case where the rotational speed is low (for example, 100 [rpm]). The frequency of the PWM signal is 10 [Hz].

  As shown in FIG. 5 (a), when the rotational speed is high, the duty ratio of the PWM signal increases, and therefore the fluctuation range of the rotational speed decreases. On the other hand, as shown in FIG. 5B, when the rotational speed is low, the duty ratio of the PWM signal becomes small and the fluctuation range of the rotational speed becomes large. And the problem that a vibration and abnormal noise generate | occur | produce arises from the fluctuation | variation of this rotation speed.

  The present invention has been made to solve such a conventional problem, and the object of the present invention is to reduce the occurrence of vibration and abnormal noise even when the rotational speed is low. An object of the present invention is to provide an electric fan control device.

  In order to achieve the above object, according to the first aspect of the present invention, there is provided a control device for an electric fan that controls driving of an electric fan mounted on a vehicle. An electronic switch that controls switching and driving of the electric fan, and a rotational speed determination that determines whether the rotational speed of the electric fan is equal to or higher than a predetermined threshold rotational speed or less than the threshold rotational speed And when the rotational speed of the electric fan is greater than or equal to the threshold rotational speed, the PWM signal is set to a first frequency, and the rotational speed of the electric fan is less than the threshold rotational speed , A frequency setting means for setting the PWM signal to a second frequency higher than the first frequency, a duty ratio according to a set rotational speed inputted from the outside, and the frequency setting means It generates a PWM signal based on the set frequency, characterized by having a a PWM signal generating means for outputting to the electronic switch.

  The invention according to claim 2 further comprises a rotation speed detection means for detecting the rotation speed of the electric fan, wherein the rotation speed of the electric fan is an actual rotation speed detected by the rotation speed detection means. Features.

  The invention described in claim 3 is characterized in that the rotational speed of the electric fan is a set rotational speed input from the outside.

  According to a fourth aspect of the present invention, the electronic switch has a first heat generation amount that is a sum of energization heat generation and switching heat generation when driven by a PWM signal having a first frequency, and a PWM signal having a second frequency. It has a heat-resistant characteristic that can withstand both of the second heat generation amount that is the sum of the energization heat generation and the switching heat generation when driven by.

  The invention according to claim 5 is that the first frequency is a frequency of less than 100 [Hz], and the second frequency is a frequency of 100 [Hz] or more and less than 1 [KHz]. Features.

  In the first aspect of the invention, when the electronic switch is controlled by the low frequency PWM signal to drive the electric fan, the frequency of the PWM signal is set to the first if the rotation speed of the electric fan is equal to or higher than a predetermined threshold rotation speed. If the rotational speed of the electric fan is less than a predetermined threshold rotational speed, the frequency of the PWM signal is set to the second frequency. Therefore, since the frequency is set high when the duty ratio of the PWM signal is small, fluctuations in the rotational speed of the electric fan can be suppressed low, and the occurrence of vibration and abnormal noise can be reduced.

  In the second aspect of the invention, since the rotational speed detected by the rotational speed detection means is used as the rotational speed of the electric fan, it is possible to control the electric fan suitable for the actual driving situation of the electric fan.

  In the invention of claim 3, since the set rotational speed inputted from the outside is used as the rotational speed of the electric fan, it is not necessary to provide a rotational speed detecting means, the apparatus configuration can be simplified, and the cost can be reduced. Can be planned.

  In the invention of claim 4, an electronic switch having a specification having heat resistance characteristics that can withstand both the first calorific value and the second calorific value is used. Here, the amount of heat generated in the electronic switch includes switching heat generation that increases as the frequency of the PWM signal increases and energization heat generation that increases as the duty ratio of the PWM signal increases. When the electronic switch is driven by the PWM signal of the first frequency, the duty ratio is large due to the low frequency, and when the electronic switch is driven by the PWM signal of the second frequency, the duty is high by the high frequency. Since the ratio is low, the total heat generation amount, that is, the first heat generation amount and the second heat generation amount are substantially equal. For this reason, it is not necessary to set the heat resistance characteristics of the electronic switch to be larger than necessary, and the apparatus scale can be reduced and the cost can be reduced.

  In the invention of claim 5, since the frequency of the PWM signal is less than 1 [KHz], when using such a low frequency region PWM signal, noise caused by the electric fan can be reliably reduced. it can.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the electric fan control device according to the first embodiment of the present invention. As shown in FIG. 1, a positive output terminal of a battery VB (power supply) mounted on the vehicle is connected to the ground via an electronic switch T1 (eg, MOSFET) and an electric fan F1. Further, the control terminal of the electronic switch T1 is connected to the control device 10. Therefore, driving and stopping of the electric fan F1 can be switched by controlling the electronic switch T1. Further, the electric fan F1 is provided with a rotation sensor (rotation speed detecting means) 15 for detecting the rotation speed of the electric fan F1.

  The control device 10 includes a duty ratio setting unit (duty ratio setting means) 11 for setting the duty ratio of the PWM signal based on the set rotational speed input from the external operation element 16 and an electric fan detected by the rotation sensor 15. A rotation speed determination unit (rotation speed determination means) 13 for determining whether the rotation speed of F1 is equal to or higher than a preset threshold rotation speed or less than the threshold rotation speed, and determination by the rotation speed determination section 13 Based on the result, a frequency setting unit (frequency setting means) 14 for setting the frequency of the PWM signal, and a PWM signal having a frequency set by the frequency setting unit 14 and a duty ratio set by the duty ratio setting unit 11 And a PWM generator (PWM signal generating means) 12 for outputting to the control terminal (the gate of the MOSFET) of the electronic switch T1.

  The duty ratio setting unit 11 includes correspondence data indicating a correspondence relationship between the set rotational speed input from the external operation element 16 and the duty ratio, and when the set rotational speed is input, the duty corresponding to the data is set. Set the ratio. For example, when the rotation speed 500 [rpm] is input as the set rotation speed, the duty ratio is set to 50%.

  When the actual rotational speed detected by the rotational sensor 15 is equal to or higher than a preset threshold rotational speed (for example, 200 [rpm]), the rotational speed determination unit 13 outputs a low frequency setting signal and sets When the rotation speed is less than the threshold rotation speed, a high frequency setting signal is output.

  When the low frequency setting signal is input from the rotation speed determination unit 13, the frequency setting unit 14 sets the frequency of the PWM signal to the first frequency f1 (less than 100 [Hz], for example, 10 [Hz]). When the high frequency setting signal is input, the frequency of the PWM signal is set to the second frequency f2 (less than 1 [KHz], for example, 100 [Hz]) higher than the first frequency. That is, when the set rotational speed of the electric fan F1 is less than the threshold rotational speed, the frequency is set to the second frequency f2, and when the set rotational speed of the electric fan F1 is equal to or higher than the threshold rotational speed, the frequency is set to the second frequency f2. 1 frequency f1 (f1 <f2).

  In the PWM generator 12, for example, the frequency set by the frequency setting unit 14 is the first frequency f1 (10 [Hz]), and the duty ratio set by the duty ratio setting unit 11 is 50%. In this case, a PWM signal having the frequency and the duty ratio is generated, and the generated PWM signal is output to the control terminal of the electronic switch T1.

  The electronic switch T1 has such a heat resistance characteristic that it can withstand both a temperature rise due to heat generation during driving at the first frequency f1 and a temperature rise due to heat generation during driving at the second frequency f2. ing. Hereinafter, this will be described in detail with reference to FIG.

  The temperature of the electronic switch T1 rises mainly due to switching heat generation and energization heat generation. Switching heat generation is heat generation due to an on / off operation when the electronic switch T1 is PWM-driven, and energization heat generation is heat generation due to a current flowing through the electronic switch T1. The temperature of the electronic switch T1 rises due to the total heat generation of these switching heat generation and energization heat generation.

  Here, the switching heat generation rises almost in proportion to the frequency of the PWM signal. That is, as shown in FIG. 4B, the heat generation amount increases as the frequency increases. Further, the energization heat generation increases substantially in proportion to the energization time, that is, the duty ratio. That is, the heat generation amount increases as the duty ratio of the PWM signal increases.

  FIG. 4A shows the heat generation amount (first heat generation amount) when the electronic switch T1 is driven by the PWM signal having the first frequency f1, and the electronic switch T1 using the PWM signal having the second frequency f2. The calorific value (second calorific value) when driving is shown.

  As described above, when the set rotational speed is high (when the rotational speed is equal to or higher than the threshold rotational speed), the duty ratio is set to be large, and the frequency is set to the first frequency f1, which is a low frequency. Therefore, although energization heat generation becomes large, switching heat generation becomes small, and the total heat generation amount is in the vicinity of Q1 shown in FIG.

  On the other hand, when the set rotational speed is low (when the rotational speed is less than the threshold rotational speed), the duty ratio is set small, and the frequency is set to the second frequency f2, which is a high frequency. Therefore, although the switching heat generation becomes large, the energization heat generation becomes small, and the total heat generation amount is in the vicinity of Q1 shown in FIG.

  Therefore, when the electronic switch T1 is driven by the PWM signal having the first frequency f1 and when the electronic switch T1 is driven by the PWM signal having the second frequency f2, the overall heat generation amount is substantially the same. The amount is Q1. Therefore, if the heat resistance characteristic of the electronic switch T1 is set to a characteristic that can withstand a heat generation amount slightly higher than the heat generation amount Q1, the case where the electronic switch T1 is driven by the PWM signal having the first frequency f1, and the first In both cases where the electronic switch T1 is driven by the PWM signal having the frequency f2 of 2, it is possible to prevent troubles such as deterioration and damage due to heat generation.

  Next, the operation of the electric fan control device according to the first embodiment configured as described above will be described with reference to the flowchart shown in FIG.

  In step S11, the set rotational speed is read. In this process, the duty ratio setting unit 11 receives the set rotational speed output from the external operator 16 and recognizes the set rotational speed. If this process ends, the process proceeds to step S12.

  In step S12, the actual rotational speed is read. In this process, the rotation speed determination unit inputs the actual rotation speed of the electric fan F1 detected by the rotation sensor 15, and recognizes the actual rotation speed. If this process ends, the process proceeds to step S13.

  In step S13, it is determined whether or not the actual rotational speed recognized in the process in step S12 is greater than or equal to the threshold rotational speed or less than the threshold rotational speed. In this process, the rotational speed determination unit 13 compares the actual rotational speed with a preset threshold rotational speed (for example, 200 [rpm]). If it is determined that the actual rotational speed is greater than or equal to the threshold rotational speed, the process proceeds to step S14. If it is determined that the set rotational speed is less than the threshold rotational speed, the process proceeds to step S15. To do.

  In step S14, processing for setting the frequency of the PWM signal to the first frequency f1 is executed. In this process, the frequency setting unit 14 sets the frequency of the PWM signal to the first frequency f1 (for example, 10 [Hz]). If this process ends, the process proceeds to step S16.

  In step S15, processing for setting the frequency of the PWM signal to the second frequency f2 is executed. In this process, the frequency setting unit 14 sets the frequency of the PWM signal to the second frequency f2 (for example, 100 [Hz]). If this process ends, the process proceeds to step S16.

  In step S16, a process for setting the duty ratio is executed. In this process, the duty ratio setting unit 11 sets the PWM duty ratio corresponding to the set rotational speed recognized in the process of step S11. When this process ends, the process proceeds to step S17.

  In step S17, processing for generating a PWM signal is executed. In this process, the PWM generator 12 is based on the duty ratio set by the duty ratio setting unit 11 and the frequency (first frequency f1 or second frequency f2) set by the frequency setting unit 14. A PWM signal is generated. When this process ends, the process proceeds to step S18.

  In step S18, control of the electronic switch T1 is executed. In this processing, the PWM generator 12 outputs the generated PWM signal to the control terminal (for example, the gate of the MOSFET) of the electronic switch T1, and drives the electronic switch T1.

  Thus, the electronic switch T1 is controlled by switching the low frequency (first frequency f1) and the high frequency (second frequency f2) according to the actual rotational speed detected by the rotation sensor 15, and the electric fan F1 is driven. It can be done.

  FIG. 3 is a characteristic diagram showing the amount of fluctuation of the rotational speed of the electric fan F1, FIG. 3 (a) shows a case where the rotational speed is high, and FIG. 3 (b) shows a case where the rotational speed is low. As shown in FIG. 3A, when the rotational speed is high, the duty ratio is set to be large, and it is understood that the amount of fluctuation of the rotational speed is small. On the other hand, as shown in FIG. 3B, it is understood that when the rotational speed is low, the frequency is set high, so that the fluctuation amount of the rotational speed is small.

  In this way, in the electric fan control device according to the first embodiment, the electronic switch T1 is controlled by the PWM signal having a low frequency of less than 1 [KHz], and the electric fan F1 is driven, so 20 [KHz]. Compared with the case where a high frequency is used, noise can be reduced, and the cost and size of electronic components can be reduced.

  In the electric fan control device according to the present embodiment, when the actual rotational speed detected by the rotation sensor 15 is equal to or higher than a preset threshold rotational speed, the frequency of the PWM signal is set to the first frequency f1. (Less than 100 [Hz], for example, 10 [Hz]) When the rotation speed is less than the threshold rotation speed, the frequency of the PWM signal is less than the second frequency f2 (f2> f1, 1 [KHz], for example, 100 [Hz]).

  Therefore, when the actual rotational speed is high, as shown in FIG. 3 (a), the fluctuation amount of the rotational speed is reduced, and the occurrence of vibration and abnormal noise can be reduced. Even when the actual rotational speed is low, as shown in FIG. 3B, the amount of fluctuation of the rotational speed is reduced by setting the frequency of the PWM signal to the second frequency f2, which is a high frequency. It is also possible to prevent the occurrence of vibration and abnormal noise.

  Further, when the actual rotational speed is low, the frequency of the PWM signal is set to the second frequency f2, which is a high frequency, and the switching heat generation becomes large. However, in this case, since the duty ratio is low, the energization heat generation is reduced, and the overall heat generation amount is suppressed to a low value. That is, in both cases where the frequency of the PWM signal is set to the first frequency f1 and the electronic switch T1 is driven, and when the electronic switch T1 is driven to be set to the second frequency f2. The calorific value is in the vicinity of the calorific value Q1 shown in FIG. Accordingly, it is not necessary to improve the heat resistance characteristics of the electronic switch T1 and other components accompanying the use of a high frequency (second frequency f2), and the cost can be reduced and the device scale can be reduced. .

  Next, a second embodiment of the present invention will be described. FIG. 5 is a block diagram showing the configuration of the electric fan driving device according to the second embodiment of the present invention. As shown in FIG. 5, the positive output terminal of a battery VB (power supply) mounted on the vehicle is connected to the ground via an electronic switch T1 (eg, MOSFET) and an electric fan F1. Further, the control terminal of the electronic switch T1 is connected to the control device 10. Therefore, driving and stopping of the electric fan F1 can be switched by controlling the electronic switch T1.

  The control device 10 has a duty ratio setting unit (duty ratio setting means) 11 for setting the duty ratio of the PWM signal based on the set rotational speed input from the external operation element 16, and the set rotational speed is preset. Based on the determination result by the rotation speed determination section (rotation speed determination means) 13 that determines whether the rotation speed is equal to or higher than the threshold rotation speed or less than the threshold rotation speed, the frequency of the PWM signal A frequency setting unit (frequency setting means) 14 for setting the frequency, a PWM signal having a frequency set by the frequency setting unit 14 and a duty ratio set by the duty ratio setting unit 11 is generated, and the electronic switch T1 And a PWM generator (PWM signal generating means) 12 for outputting to a control terminal (MOSFET gate).

  The duty ratio setting unit 11 includes correspondence data indicating a correspondence relationship between the set rotational speed input from the external operation element 16 and the duty ratio, and when the set rotational speed is input, the duty corresponding to the data is set. Set the ratio. For example, when the rotation speed 500 [rpm] is input as the set rotation speed, the duty ratio is set to 50%.

  The rotational speed determination unit 13 outputs a low-frequency setting signal when the set rotational speed input from the external operator 16 is equal to or higher than a preset threshold rotational speed (for example, 200 [rpm]), When the set rotational speed is less than the threshold rotational speed, a high frequency setting signal is output.

  When the low frequency setting signal is input from the rotation speed determination unit 13, the frequency setting unit 14 sets the frequency of the PWM signal to the first frequency f1 (less than 100 [Hz], for example, 10 [Hz]). When the high frequency setting signal is input, the frequency of the PWM signal is set to the second frequency f2 (less than 1 [KHz], for example, 100 [Hz]) higher than the first frequency. That is, when the set rotational speed of the electric fan F1 is less than the threshold rotational speed, the frequency is set to the second frequency f2, and when the set rotational speed of the electric fan F1 is equal to or higher than the threshold rotational speed, the frequency is set to the second frequency f2. 1 frequency f1 (f1 <f2).

  In the PWM generator 12, for example, the frequency set by the frequency setting unit 14 is the first frequency f1 (10 [Hz]), and the duty ratio set by the duty ratio setting unit 11 is 50%. In this case, a PWM signal having the frequency and the duty ratio is generated, and the generated PWM signal is output to the control terminal of the electronic switch T1.

  Next, the operation of the electric fan control device according to the second embodiment configured as described above will be described with reference to the flowchart shown in FIG.

  In step S21, the set rotational speed is read. In this process, the duty ratio setting unit 11 and the rotation speed determination unit 13 input the set rotation speed output from the external operator 16 and recognize the set rotation speed. When this process ends, the process proceeds to step S22.

  In step S22, it is determined whether the set rotational speed is equal to or higher than the threshold rotational speed or less than the threshold rotational speed. In this process, the rotational speed determination unit 13 compares the set rotational speed with a preset threshold rotational speed (for example, 200 [rpm]). If it is determined that the set rotational speed is greater than or equal to the threshold rotational speed, the process proceeds to step S23. If it is determined that the set rotational speed is less than the threshold rotational speed, the process proceeds to step S24. To do.

  In step S23, processing for setting the frequency of the PWM signal to the first frequency f1 is executed. In this process, the frequency setting unit 14 sets the frequency of the PWM signal to the first frequency f1 (for example, 10 [Hz]). When this process ends, the process proceeds to step S25.

  In step S24, processing for setting the frequency of the PWM signal to the second frequency f2 is executed. In this process, the frequency setting unit 14 sets the frequency of the PWM signal to the second frequency f2 (for example, 100 [Hz]). When this process ends, the process proceeds to step S25.

  In step S25, a process for setting the duty ratio is executed. In this process, the duty ratio setting unit 11 sets the PWM duty ratio corresponding to the set rotational speed. When this process ends, the process proceeds to step S26.

  In step S26, processing for generating a PWM signal is executed. In this process, the PWM generator 12 is based on the duty ratio set by the duty ratio setting unit 11 and the frequency (first frequency f1 or second frequency f2) set by the frequency setting unit 14. A PWM signal is generated. If this process ends, the process proceeds to step S27.

  In step S27, control of the electronic switch T1 is executed. In this processing, the PWM generator 12 outputs a PWM signal to the control terminal (for example, the gate of the MOSFET) of the electronic switch T1, and drives the electronic switch T1.

  Thus, the electric switch F1 can be driven by switching the low frequency (first frequency f1) and the high frequency (second frequency f2) according to the set rotational speed to control the electronic switch T1.

  In this way, the electric fan control device according to the second embodiment also controls the electronic switch T1 with the PWM signal having a low frequency of less than 1 [KHz], as in the first example, and the electric fan. Since F1 is driven, noise can be reduced as compared with the case where a high frequency of about 20 [KHz] is used, and the cost and size of electronic components can be reduced, and noise can be reduced. Can be prevented.

  Further, since it is not necessary to provide the rotation sensor 15 (see FIG. 1) as compared with the first embodiment described above, the configuration can be simplified, and further downsizing and cost reduction can be achieved. .

  As mentioned above, although the drive device of the electric fan of this invention was demonstrated based on embodiment of illustration, this invention is not limited to this, The structure of each part is set to the thing of the arbitrary structures which have the same function. Can be replaced.

  For example, the case where a MOSFET is used as the electronic switch T1 has been described as an example, but an IGBT (insulated gate bipolar transistor) or the like may be used.

  The control device for an electric fan according to the present invention is extremely useful for preventing the occurrence of vibration and abnormal noise when the electric fan is driven by a low-frequency PWM signal.

It is a block diagram which shows the structure of the control apparatus of the electric fan which concerns on 1st Embodiment of this invention. It is a flowchart which shows the process sequence of the control apparatus of the electric fan which concerns on 1st Embodiment of this invention. It is a characteristic view which shows the change of the rotation speed of the electric fan controlled using the control apparatus of the electric fan which concerns on 1st Embodiment of this invention, (a) is when rotation speed is high, (b) is rotation The case where the number is low is shown. It is explanatory drawing which shows the emitted-heat amount of the control apparatus of the electric fan which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structure of the control apparatus of the electric fan which concerns on 2nd Embodiment of this invention. It is a flowchart which shows the process sequence of the control apparatus of the electric fan which concerns on 2nd Embodiment of this invention. It is a characteristic view which shows the change of the rotation speed of the electric fan in the past, (a) shows the case where a rotation speed is high, (b) shows the case where a rotation speed is low.

Explanation of symbols

10 control device 11 duty ratio setting section (duty ratio setting means)
12 PWM generator (PWM generation means)
13 Rotational speed determination unit (rotational speed determination means)
14 Frequency setting part (frequency setting means)
15 Rotation sensor (Rotation speed detection means)
16 External controller VB Battery (Power supply)
T1 electronic switch F1 electric fan

Claims (5)

In an electric fan control device for controlling the driving of an electric fan mounted on a vehicle,
An electronic switch for controlling the driving and stopping of the electric fan by switching conduction and interruption of power output from the power supply by a PWM signal;
A rotational speed determination means for determining whether the rotational speed of the electric fan is equal to or higher than a predetermined threshold rotational speed or less than the threshold rotational speed;
When the rotation speed of the electric fan is equal to or higher than the threshold rotation speed, the PWM signal is set to the first frequency, and when the rotation speed of the electric fan is less than the threshold rotation speed, the PWM signal is set. Frequency setting means for setting a signal to a second frequency higher than the first frequency;
PWM signal generating means for generating a PWM signal based on a duty ratio according to a set rotational speed inputted from the outside and a frequency set by the frequency setting means, and outputting the PWM signal to the electronic switch;
A control device for an electric fan, comprising:   The rotation speed detection means for detecting the rotation speed of the electric fan is further provided, and the rotation speed of the electric fan is an actual rotation speed detected by the rotation speed detection means. Control device for electric fan.   2. The electric fan control device according to claim 1, wherein the rotational speed of the electric fan is a set rotational speed input from the outside.   The electronic switch has a first heat generation amount that is a sum of energization heat generation and switching heat generation when driven by a PWM signal of a first frequency, and energization heat generation and switching when driven by a PWM signal of a second frequency. The electric fan control device according to any one of claims 1 to 3, further comprising a heat-resistant characteristic capable of withstanding both of a second heat generation amount that is a sum of heat generation.   The first frequency is a frequency less than 100 [Hz], and the second frequency is a frequency of 100 [Hz] or more and less than 1 [KHz]. 5. The electric fan control device according to claim 4.

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