JP6856306B2 - Electronic devices, fan control programs and fan control methods - Google Patents

Description

The present invention relates to controlling the rotation speed of a fan (blower) of an electronic device mounted on a vehicle such as an automobile.

An in-vehicle device mounted on an automobile such as a moving body is provided with a fan (blower) in order to suppress an increase in temperature of internal operation. By rotating the fan, an air flow is created and the part that generates heat is forcibly air-cooled, while the rotation of the fan generates noise. For example, Patent Document 1 controls to gradually increase or decrease the rotation speed of the fan motor in order to reduce an unpleasant noise caused by the rotation of the fan motor of the air conditioning indoor unit. Further, Patent Document 2 controls to smoothly increase the rotation speed of the fan in order to suppress noise at the time of starting the fan.

Japanese Unexamined Patent Publication No. 2014-055745 JP-A-2007-065871

Some in-vehicle devices perform fan control that changes the rotation speed of the fan according to the volume of the output voice. That is, the control is such that the rotation speed of the fan is increased when the volume of the output voice is increased, and the rotation speed of the fan is decreased when the volume is decreased. By such fan control, the heat dissipation efficiency is improved while preventing the noise generated by the fan from being offensive to the ears due to the output voice.

However, controlling the rotation speed of the fan according to the volume of the output voice has the following problems. For example, when the volume of the output sound suddenly increases, the rotation speed of the fan also suddenly increases in a short time, and the change in the rotation speed of the fan in a short time causes a growl. There is. The noise caused by the rotation of the fan is caused by the wind noise of the fan cutting the wind and the rotational vibration of the fan transmitted to the housing. When the rotation speed of the fan is constant, a certain amount of noise is generated, but when the rotation speed of the fan changes, the wind noise that switches instantly and the housing that switches late while being transmitted through the housing. A roaring sound is generated by combining with the vibration sound of the body.

FIG. 8 illustrates the mechanism of roaring sound generation. A fan is built in the housing 10 of the in-vehicle device, a wind noise S1 is generated from a portion of the housing 10 close to the fan, and the wind noise S1 and vibration of the fan are transmitted to the housing 10. , The vibration sound S2 delayed from the wind noise S1 of the fan is generated from the housing 10. A roaring sound is generated from the housing 10 due to a slight difference in frequency between the wind sound S1 and the vibration sound S2. The frequency at which this growl is generated is the difference between the respective frequencies, and the amplitude is the sum of the respective amplitudes.

FIG. 9 is a graph showing the relationship between the change in the volume of the output voice and the change in the rotation speed of the fan. The upper waveform shows the change in volume, and indicates that the volume is high in the part where the vibration is dense and the volume is low in the part where the vibration is sparse. The waveform below shows the change in fan speed. When the volume of the output voice changes greatly, the rotation speed of the fan changes greatly accordingly, and a loud growl is generated during the changing period.

The fan has a structure in which a plurality of blades are rotated and air is periodically pushed out by the blades, and strong noise (peak noise) is generated at a frequency corresponding to the rotation speed. The relational expression between the fan speed and the peak noise frequency is expressed by the following equation.
Frequency = rotation speed (rpm) / 60 (seconds) x number of blades For example, when a 5-blade fan is rotated at 2880 rpm, strong noise is generated at 240 Hz according to the above relational expression, and when it is rotated at 4320 rpm. Strong noise is generated at 360 Hz. FIG. 10 shows each noise waveform when a fan having five blades is rotated at 2880 rpm and 4320 rpm. The horizontal axis is the frequency (Hz), and the vertical axis is the noise level (dB).

When the rotation speed of the 5-blade fan changes from 4000 rpm to 6000 rpm, the noise peak at 4000 rpm is 333 Hz and the noise peak at 6000 rpm is 500 Hz, and the maximum growl is the frequency of both. It occurs at 167 Hz, which is the difference between the two. When the rotation speed of the fan increases, the noise increases in proportion to the rotation speed, so that the roaring sound is very jarring to the ears.

Further, when the rotation speed of the fan changes from 4000 rpm to 5000 rpm, the maximum roaring sound frequency is 88 Hz, which is lower than the case where the rotation speed increases by 2000 rpm as described above, so that the roaring sound can be experienced. It doesn't bother me so much. On the other hand, when the rotation speed of the fan is lowered from 6000 rpm to 4000 rpm, the maximum roaring sound is generated at 167 Hz, but the noise becomes smaller in proportion to the rotation speed, so that the roaring sound is not so jarring as a sensation.

An object of the present invention is to solve such a conventional problem, and to provide an electronic device, a fan control program, and a fan control method for controlling the rotation speed of a fan so that noise caused by the fan does not disturb the ears. To do.

The electronic device according to the present invention has a cooling fan built in the housing, and the fan rotates according to the sound output means for outputting the sound and the volume of the sound output from the sound output means. It has a fan control means for controlling the number, and the fan control means controls so that the rotation speed of the fan increases stepwise when the amount of change in the rotation speed of the fan increases by a certain value or more.

Preferably, the fan control means controls so that the rotation speed of the fan increases as the volume of the output voice increases, and the rotation speed of the fan decreases as the volume of the output voice decreases. Preferably, the fan control means makes the step width when the rotation speed is gradually increased smaller than the constant value. Preferably, the fan control means is such that the frequency of the peak of the roaring sound calculated from the relational expression of frequency = rotation speed (rpm) / 60 (seconds) × number of fan blades is equal to or less than a determined value. Set the step width. Preferably, the fan control means controls so that when the amount of change in the rotation speed of the fan decreases by the certain value or more, the rotation speed of the fan decreases at once to the target rotation speed. Preferably, the fan control means includes a detection means for detecting the volume of the output voice and a determination means for determining the rotation speed of the fan based on the volume detected by the detection means. The amount of change in the rotation speed is calculated from the difference between the rotation speed of the fan and the rotation speed determined by the determination means.

The fan control program according to the present invention is executed by an electronic device having a cooling fan built in a housing and having an audio output means for outputting audio, and the audio is output from the audio output means. At that time, a step of detecting the volume of the output sound, a step of determining the rotation speed of the target fan based on the detected volume, and a change between the current rotation speed of the fan and the rotation speed of the target fan. When the amount increases by a certain value or more, it has a step of gradually increasing the rotation speed of the fan to the target rotation speed of the fan.

The fan control method according to the present invention is in an electronic device having a cooling fan built in a housing and having an audio output means for outputting audio, and when audio is output from the audio output means. , The step of detecting the volume of the output sound, the step of determining the rotation speed of the target fan based on the detected volume, and the amount of change between the current rotation speed of the fan and the rotation speed of the target fan. When it increases by a certain value or more, it has a step of gradually increasing the rotation speed of the fan to the target rotation speed of the fan.

According to the present invention, when the amount of change in the rotation speed of the fan increases by a certain value or more, the rotation speed of the fan is gradually increased, so that the roar generated from the housing due to the rotation of the fan It is possible to prevent noise such as sound from being offensive to the ears and reduce discomfort given to the user.

It is a block diagram which shows the structure of the vehicle-mounted device which concerns on embodiment of this invention. It is a figure explaining the detail of the fan drive part which concerns on embodiment of this invention. FIG. 3A is a diagram showing a functional configuration of a fan control program according to an embodiment of the present invention, and FIG. 3B is a table defining the relationship between the volume of output audio and the rotation speed level of the fan. is there. It is an operation flow of the fan control which concerns on embodiment of this invention. It is an operation flow which shows an example of the control of the rotation speed according to the level change which concerns on embodiment of this invention. It is a figure explaining some operation pattern of the fan control which concerns on embodiment of this invention. It is a figure which shows the specific example change of the rotation speed of the fan of each operation pattern of FIG. It is a graph which shows the change of the rotation speed of the fan which concerns on embodiment of this invention. It is a figure explaining the generation mechanism of the growl sound of an in-vehicle device. It is a graph which shows the relationship between the volume change of an output voice, and the change of the rotation speed of a fan. It is a waveform diagram which shows the relationship between the frequency of the noise generated by the rotation of a fan, and the noise level.

Next, an embodiment of the present invention will be described in detail with reference to the drawings. The electronic device according to the present invention can be an in-vehicle device fixedly mounted on a moving body such as an automobile, a portable computer device that can be carried around, or a tablet-type computer device. Further, the electronic device according to the present invention can be equipped with a function of reproducing audio data and video data, a function of receiving television / radio broadcasts, a navigation function, and the like. Further, the electronic device according to the present invention has a cooling function for suppressing a temperature rise inside the device. The cooling function includes at least one fan and forcibly cools the heat generating portion by the rotation of the fan.

FIG. 1 is a block diagram showing a configuration of an in-vehicle device according to an embodiment of the present invention. The in-vehicle device 100 includes a user input unit 110, a navigation unit 120, a multimedia playback unit 130, a display unit 140, a voice output unit 150, a storage unit 160, a fan drive unit 170, and a vehicle information acquisition unit 180. However, the configuration shown here is an example, and the in-vehicle device 100 may include other functions and configurations.

The user input unit 100 receives an instruction from the user and provides the instruction to the control unit 190. The navigation unit 120 calculates the position of the own vehicle by a GPS satellite or a self-contained navigation sensor, and guides the road around the position of the own vehicle. The multimedia reproduction unit 130 reproduces audio signals and video signals recorded on recording media such as CDs, DVDs, and semiconductor devices. The reproduced video signal is output from the display unit 140, and the audio signal is output from the audio output unit 150. Further, the multimedia reproduction unit 130 may include a television / radio reception function.

The storage unit 160 can store information required for the navigation unit 120 and the multimedia playback unit 130, application software and programs executed by the control unit 190, and the like. The fan drive unit 170 includes one or a plurality of fans (blowers), rotates the fans under the control of the control unit 190, and forcibly cools the inside of the vehicle-mounted device 100 by air cooling. The vehicle information acquisition unit 180 acquires information on the engine speed and other operations of the vehicle and provides the information to the control unit 190. The control unit 190 controls each unit of the vehicle-mounted device 100.

FIG. 2 describes the details of the fan drive unit 170 according to the present embodiment. The fan drive unit 170 responds to the fan rotation speed control unit 210 that controls the rotation speed of the fan 230 based on the volume of the output sound set by the volume setting unit 200, and the rotation speed controlled by the fan rotation speed control unit 210. It has a drive circuit 220 that drives the fan 230, and a fan 230 that rotates based on a drive signal from the drive circuit 220.

The volume setting unit 200 sets the volume of the audio signal from the source 130 (for example, the multimedia reproduction unit 130). In other words, the volume of the sound output by the sound output unit 150 is set. The control unit 190 or the multimedia playback unit 130 automatically sets the volume of the volume setting unit 200 according to the volume information associated with the output sound, or the user changes the volume to change the volume of the volume setting unit 200. It is possible to set.

The fan 230 is built in the housing of the in-vehicle device 100. The fan 230 has a plurality of blades and generates wind by rotating the plurality of blades. The number and shape of the blades of the fan 230 are not particularly limited. The volume setting unit 200 may be included in the control unit 190, the audio output unit 150, or the multimedia playback unit 130, and the fan rotation speed control unit 210 is included in the control unit 190. There may be.

In a preferred embodiment, the fan rotation speed control unit 210 is composed of a microcontroller including a ROM, RAM, and the like, and controls the operation of the fan 230 by executing a program for controlling the rotation speed of the fan.

FIG. 3 is a diagram showing a functional configuration of the fan control program according to the present embodiment. The fan control program 300 includes a volume detection unit 310, a rotation speed level determination unit 320, a level change determination unit 330, and a rotation speed setting unit 340.

The volume detection unit 310 detects the volume of the output voice set by the volume setting unit 200. The rotation speed level determination unit 320 determines the rotation speed level of the fan based on the volume detected by the volume detection unit 310. The rotation speed level represents the rotation speed of the target target. In one example, as shown in FIG. 3B, a table defining the relationship between the volume and the rotation speed level is stored in the storage unit 160, and the rotation speed level determination unit 320 refers to and sets this table. Determine the number of revolutions level corresponding to the volume. For example, if the volume is VOL_0 to 20, the rotation speed level is 1 (A_rpm), if the volume is VOL_1-40, the rotation speed level is 2 (B_rpm), and if the volume is VOL_160, the rotation speed level is 3 (C_rpm). Is. In this case, there is a relationship of A <B <C.

The level change determination unit 330 compares the current rotation speed level of the fan with the target rotation speed level determined by the rotation speed level determination unit 320, and increases or decreases the rotation speed, and the rotation speed. Judge the amount of change in. That is, it is determined whether the current rotation speed-the target rotation speed is positive or negative, and the amount of change is calculated from the difference of | current rotation speed-target rotation speed |. For example, when the fan is rotating at 3000 rpm and it is determined to rotate at 4000 rpm as the volume of the output sound increases, the level change determination unit 330 increases the fan rotation speed (positive). , It is determined that the amount of change in the number of revolutions is 1000 rpm. Further, when the fan is rotating at 5000 rpm and it is determined to rotate at 3000 rpm due to the decrease in the volume of the output sound, the level change determination unit 330 has a decrease (negative) in the rotation speed of the fan. , It is determined that the amount of change in the number of revolutions is 2000 rpm.

The rotation speed setting unit 340 controls the target rotation speed based on the determination result of the rotation speed level determination unit 320 and the determination result of the level change determination unit 330. The rotation speed setting unit 340 controls to increase the rotation speed step by step when the amount of change in the rotation speed increases rapidly. For example, when the rotation speed level changes from "1" to "3", the rotation speed changes stepwise from "1" to "2" and "2" to "3". Be controlled. In this case, the amount of change in the number of rotations when the number of rotations changes by one is set so that the frequency of the peak noise of the growl is equal to or less than a certain level. Further, in a preferred example, when the amount of change in the rotation speed decreases, the rotation speed setting unit 340 reduces the current rotation speed to the target rotation speed at once.

Next, FIG. 4 shows an operation flow of fan control according to this embodiment. Here, when the internal temperature of the in-vehicle device 100 is equal to or lower than a certain temperature, the fan rotation speed control unit 210 controls the rotation speed according to the volume of the output voice as normal control, and keeps the internal temperature at a constant temperature. When the temperature is exceeded, as an unusual control, the fan is rotated at a constant rotation speed regardless of the volume of the output sound, and forced air cooling is performed.

For example, when an audio signal is reproduced by the multimedia reproduction unit 130 and the reproduced audio is output from the audio output unit 150, the fan is rotated at a rotation speed corresponding to the volume of the output audio (S100). After that, for example, it is assumed that the volume of the output voice is changed by the user.

The volume detection unit 310 detects the volume set by the volume setting unit 200 (S102), and the rotation speed level determination unit 320 determines a target rotation speed level based on the detected volume (S104). Next, the level change determination unit 330 compares the current rotation speed level with the target rotation speed level, and determines whether the rotation speed increases or decreases and the amount of change in the rotation speed (S106). Next, the rotation speed setting unit 340 controls the rotation speed of the fan according to the change in the rotation speed level (S110), and if there is no change, the rotation speed of the fan is the current rotation speed. The rotation continues.

FIG. 4A shows one preferable example of the rotation speed control (S110) according to the level change. When the rotation speed increases (S200), the rotation speed setting unit 240 determines whether or not the amount of change in the rotation speed is equal to or more than a certain value (S202), and when it is equal to or more than a certain value, the rotation speed setting unit 240 rotates. Control is performed so that the number gradually increases up to the target rotation speed (S204). By increasing the number of revolutions step by step, that is, by reducing the amount of change in the number of revolutions, the frequency at which the peak of the growl is peaked is lowered so that the growl does not become jarring. In one preferred example, the step width when the rotation speed is increased stepwise is less than a constant value when determining whether or not the amount of change in the rotation speed is a certain value or more.

On the other hand, when the number of revolutions decreases (S200), or even when the number of revolutions increases, if the amount of change is less than a certain value, the number of revolutions is reduced from the current number to the target number of revolutions at once. Control is performed (S206). When the number of revolutions decreases, the noise decreases in proportion to the number of revolutions. Therefore, even if the amount of change in the number of revolutions is equal to or more than a certain value, the noise such as a growl is not so jarring. Further, even when the rotation speed increases, if the amount of change in the rotation speed is less than a certain value, the frequency of the peak roaring sound is small, so that the roaring sound is less likely to be jarring.

Next, a specific fan rotation speed control according to this embodiment will be described. FIG. 5 shows some operation patterns when the rotation speed of the fan is changed, and FIG. 6 shows the change of the rotation speed at the time of those operation patterns. Here, it is assumed that the amount of change of the rotation speed level "1" is the amount of change of the rotation speed at which the roaring sound does not disturb the user.

Pattern 1 is a case where the rotation speed level of the fan increases by one as the volume of the output voice increases. In this case, since the change amount of the rotation speed level is less than a certain value (that is, the change amount of the rotation speed is less than a certain value), the rotation speed setting unit 340 sets the current rotation speed to the target rotation speed at once. Perform increasing control. In the example of FIG. 6, it is decided to raise the rotation speed level from "1" to "2" at the time T1, and the rotation speed level of 4000 rpm is the rotation speed level during a short period from the time T1 to the time T2. It is raised to 5000 rpm of 2 at a stretch. For example, when the fan has five blades, the frequency of the peak roaring sound is 88 Hz, and since this frequency is relatively low, the roaring sound is not so noticeable as a feeling.

Pattern 2 is a case where the rotation speed level is raised by two. In this case, since the amount of change in the rotation speed is equal to or greater than a certain value, the rotation speed setting unit 340 gradually increases the rotation speed to the target rotation speed by ramp control. In the example of FIG. 6, it is decided to raise the rotation speed level from "2" to "4" at time T3, and in the period from time T3 to time T4, 5000 rpm of rotation speed level 2 is 7500 rpm of rotation speed level 4. Will be gradually increased. The step width, which is the range of increase / decrease in the number of rotations, is set within a range in which the growl does not become jarring. In one preferred example, the step width can be the amount of change in rotation speed (1000 rpm) as the rotation speed level rises by one. In another preferred example, the step width may be even smaller than 1000 rpm. In the example of FIG. 6, if the step width is 500 rpm from 5000 rpm to 7500 rpm and the fan has five blades, the frequency of the peak roaring sound is 41.6 Hz, and the roaring sound is jarring because the frequency is low. do not become. Of course, the step width is not limited to 500 rpm, and may be smaller than that, and further, the step width may be set so that the frequency of the peak roaring sound is 20 Hz or less, which is an audible sound (5 sheets). If it is a fan of blades, the step width is 240 rpm). Further, the step widths when the rotation speed is gradually increased are not all uniform and may be a combination of different step widths. For example, the step width gradually decreases as the rotation speed increases, and vice versa. In addition, the step width may be gradually increased as the number of rotations increases.

Pattern 3 is a case where the rotation speed level is lowered by two. In this case, the rotation speed setting unit 340 reduces the rotation speed at once to the target rotation speed because the rotation speed is decreasing. In the example of FIG. 6, at time T5, the rotation speed level is determined to be lowered from 4 to 2, and the rotation speed is suddenly reduced from 7500 rpm to 5000 rpm during the period from time T4 to time T6. When the number of revolutions decreases, the noise of the fan becomes small and the roaring noise is not so noticeable, so the number of revolutions can be lowered at once.

Pattern 4 is a case where the rotation speed level is lowered while the rotation speed level is being raised by two or more. In this case, the rotation speed setting unit 340 increases the rotation speed stepwise as in the case of the pattern 2, but reduces the rotation speed at once when the decision to lower the rotation speed level is made. In the example of FIG. 6, the rotation speed level is decided to be changed from 2 to 4 at the time T7, and the rotation speed level is decided to be changed from 4 to 2 at the time T8 before reaching the target rotation speed (7500 rpm). .. In this case, even if the target rotation speed (7500 rpm) is not reached, the increase in the rotation speed is stopped at the time T8, and the rotation speed is suddenly reduced to the target rotation speed (5000 rpm) between the time T8 and the time T9. ..

Pattern 5 is a case where the rotation speed level is lowered by one. In this case, the rotation speed setting unit 340 lowers the rotation speed to the target rotation speed at once, as in the pattern 3. In the example of FIG. 6, the rotation speed level is lowered by one at the time T10, and the rotation speed is lowered from 5000 rpm to 4000 rpm at once between the time T10 and the time T11.

FIG. 7 is a graph showing a change in the rotation speed of the fan when the fan is controlled according to the present embodiment. The figure shows the change in the rotation speed of the fan corresponding to the change in the volume of the output voice shown in FIG. Comparing the change in the fan rotation speed shown in FIG. 7 with the change in the fan rotation speed shown in FIG. 9, the change in the fan rotation speed according to the present embodiment is the change in the conventional fan rotation speed shown in FIG. It can be seen that the sudden change is suppressed. Suppressing a sudden change in the number of revolutions is to lower the frequency of the roaring sound, and it is possible to make the jarring roaring sound inconspicuous.

In the above embodiment, the rotation speed level is determined based on the volume of the output sound, and the rotation speed is controlled based on the determined rotation speed level. However, this determines the rotation speed of the fan based on the volume of the output sound. It is equivalent to controlling the rotation speed based on the determined rotation speed. Further, in the above embodiment, the rotation speed level is determined based on the volume of the output voice, but with or instead of this, the voice of the vehicle interior space is input from the microphone, and the fan's voice level is based on the input voice. The number of revolutions may be determined. The voice in the vehicle interior space includes road noise and the like in addition to the output voice, and fan control is performed according to the loudness of the entire vehicle interior space. Also in this case, if the amount of change in the rotation speed level or the amount of change in the rotation speed is equal to or more than a certain value, control is performed to gradually increase the rotation speed of the fan. Further, the present invention does not exclude combining other elements (for example, a temperature sensor that detects the internal temperature of an in-vehicle device) for fan control.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and modifications are made within the scope of the gist of the invention described in the claims. It can be changed.

100: In-vehicle device 110: User input unit 120: Navigation unit 130: Multimedia playback unit 140: Display unit 150: Voice output unit 160: Storage unit 170: Fan drive unit 180: Vehicle information acquisition unit 190: Control unit

Claims (8)

An electronic device that has a cooling fan built into the housing.
Audio output means to output audio and
A detection means for detecting the volume of the output voice of the voice output means, and
It has a fan control means that controls the rotation speed of the fan according to the volume detected by the detection means.
The fan control means, when the amount of change in the rotational speed of the fan as a rotation speed and a target current fan is increased above a certain value, stepwise until the rotational speed of the fan as a target rotational speed of the current fan When it is increased and does not increase beyond a certain level, it is controlled to increase from the current fan speed to the target fan speed at once.
The step width when increasing the fan rotation speed step by step is the difference in the frequency of the roaring sound of the housing calculated from the relational expression of frequency = rotation speed (rpm) / 60 (seconds) x number of fan blades. An electronic device that is set to be below a certain level. The electronic device according to claim 1, wherein the fan control means controls so that the rotation speed of the fan increases as the volume of the output voice increases and the rotation speed of the fan decreases as the volume of the output voice decreases. .. The electronic device according to claim 1, wherein the step width is set so that the difference in frequency is equal to or less than an audible sound. The electronic device according to claim 1, wherein the step width is set so as to gradually decrease as the rotation speed increases. The electron according to claim 1 to 4, wherein the fan control means controls so that the rotation speed of the fan decreases at once to the target rotation speed when the amount of change in the rotation speed of the fan decreases by the certain value or more. apparatus. Rotation said fan control means includes a determination means to determine the rotational speed of the fan based on the volume detected by the detection means, the fan control unit, which is determined by the current fan speed and the determination unit The electronic device according to any one of claims 1 to 5, wherein the amount of change in the number of rotations is calculated from the difference from the number. A fan control program executed by an electronic device that has a cooling fan built into the housing and is equipped with an audio output means that outputs audio.
When the voice is output from the voice output means, the step of detecting the volume of the output voice and
Steps to determine the target fan speed based on the detected volume,
When the amount of change between the current fan speed and the target fan speed increases by a certain value or more, the current fan speed is gradually increased to the target fan speed to be constant. When it does not increase more than that, it has a step to increase the rotation speed of the current fan to the target rotation speed at once.
The step width when increasing the fan rotation speed step by step is the difference in the frequency of the roaring sound of the housing calculated from the relational expression of frequency = rotation speed (rpm) / 60 (seconds) x number of fan blades. A fan control program that is set so that is below a certain level. It is a fan control method in an electronic device having a cooling fan built in a housing and having an audio output means for outputting audio.
When the voice is output from the voice output means, the step of detecting the volume of the output voice and
Steps to determine the target fan speed based on the detected volume,
When the amount of change between the current fan speed and the target fan speed increases by a certain value or more, the current fan speed is gradually increased to the target fan speed to be constant. When it does not increase more than that, it has a step to increase the rotation speed of the current fan to the target rotation speed at once.
The step width when increasing the fan rotation speed step by step is the difference in the frequency of the roaring sound of the housing calculated from the relational expression of frequency = rotation speed (rpm) / 60 (seconds) x number of fan blades. A fan control method that is set so that is below a certain level.

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