Rotating shaft device that blocks electromagnetic waves

Abstract

In electromagnetic wave testing of rotating electrical equipment such as motors and inverters, this invention provides an effective noise-canceling rotational transmission mechanism that transmits rotational motion while blocking unwanted noise. [Solution] By utilizing the phenomenon of cutoff frequency in a waveguide, rotation is transmitted by an insulating shaft 8, and unwanted high-frequency noise is effectively blocked by installing a metal tube housing 10 of a conductive tube that serves as a waveguide at the opening through which the shaft passes, through which the insulating rotating shaft 8 passes, and the metal tube housing 10 has dimensions such that the frequency of unwanted high frequencies is below the cutoff frequency, thereby allowing only rotational force to be transmitted.

Description

Technical Field

[0001] The present invention relates to a rotating shaft device for blocking electromagnetic waves, which has a function of blocking electromagnetic waves but transmitting rotational force, and is suitable for use in an EMC test device or the like.

Background Art

[0002] The EMC evaluation test of motors and inverters mounted on vehicles such as electric vehicles (EVs) and hybrid vehicles (HVs) is carried out in an anechoic chamber that blocks electromagnetic waves. Conventionally, the EMC test of in-vehicle devices has been carried out in this anechoic chamber. However, in the tests of motors and inverters used in EVs / HVs, etc., requirements for tests while applying a load to the test motor in the same manner as actual operation have been defined by international standards. That is, the international standard requires an EMC test while realizing power running and regeneration as in an actual vehicle, rather than simply idling the motor. For this purpose, an EMC test while rotating the shaft through the wall of the anechoic chamber, connecting the test motor and the dynamometer outside the anechoic chamber with the rotating shaft, and performing various controls such as rotating the test motor or making it a load, which has not been used in the conventional anechoic chamber for EMC, has come to be required.

[0003] To conduct such EMC tests, it is necessary to drill a hole in the shielding wall of the anechoic chamber and allow the rotating shaft to pass through, resulting in electromagnetic waves traveling back and forth between the inside and outside of the anechoic chamber. The switching frequency of the inverter controlling the equipment's dynamometer, which is several kHz, generates harmonics, and in Japan, unwanted electromagnetic waves are generated up to several tens of MHz, which is the frequency band of FM broadcasting. In reality, the intensity of these electromagnetic waves is very high, reaching 1 million μV or 100,000 μV / m when expressed as voltage and electric field. On the other hand, the permissible high-frequency noise level required by international standards is a very small level, a few μV or a few μV / m in terms of voltage and electric field. Therefore, in order to attenuate the unwanted electromagnetic waves propagating through the rotating shaft, measures have been taken to prevent their intrusion into the anechoic chamber using bearings, grounding, and conductive brushes. However, it is extremely difficult to completely eliminate these unwanted electromagnetic waves. The small amount of unwanted electromagnetic noise that remains cannot be said to have absolutely no effect on precise EMC measurements.

[0004] Patent Document 1 discloses a device for transmitting rotation both inside and outside an anechoic chamber, but in exchange for high-speed rotation performance achieved by using a carbon fiber reinforced plastic shaft, there was an area where noise suppression was not complete.

[0005] Patent Document 2 discloses an EMC test system that uses a fluid motor to transmit rotation between the inside and outside of an anechoic chamber using a working fluid, but this system inherently requires a special and complex means such as a fluid motor.

[0006] Patent Document 3 discloses an automobile test system installed in a test room equipped with a test specimen placement space above the floor and an underfloor space below the floor, separated by a floor, to solve the problem that when the automobile under test and the dynamometer are placed in the same room, the noise, vibration and electromagnetic noise generated by the dynamometer itself interfere with the test and prevent proper testing. The system has a support mechanism that rotatably supports the drive shaft connected to the inner ring of the hub bearing of the automobile under test, a dynamometer installed in the underfloor space, and a system that transmits the rotational power of the dynamometer's output shaft as the rotational power of the automobile's drive shaft. However, this system transmits rotational force between the automobile's axle and the dynamometer and does not enable EMC testing of motors and inverters. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2021-141165 [Patent Document 2] Special Publication No. 2021-517648 [Patent Document 3] Japanese Patent Publication No. 2023-022670 [Overview of the project] [Problems that the invention aims to solve]

[0008] As mentioned above, conventional methods using conductive rotating shafts have the problem that it is not possible to completely prevent noise from propagating inside and outside the anechoic chamber. Furthermore, the noise propagated by conventional technology, depending on the frequency, far exceeded the noise level of several μV or several μV / m required for EMC testing.

[0009] Suppressing the propagation of such electromagnetic noise is a challenge not only in EMC testing, but also in preventing malfunctions of measuring instruments caused by electromagnetic noise on dynamo test benches during motor / inverter development. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the inventors of this invention conducted research and development on a structure that makes the rotating shaft a complete insulator and further suppresses the propagation of electromagnetic noise at the penetration portion of the shield wall, resulting in the completion of the present invention. In other words, the present invention focuses on the fact that the cutoff frequency of electromagnetic wave propagation in a tubular conductor can be utilized by using a conductive cylindrical through-tube positioned outside the rotating shaft. By utilizing the cutoff frequency of the conductive shield through-tube and blocking direct propagation along the shaft by the insulating rotating shaft, the present invention effectively blocks and suppresses high-frequency noise below a specific frequency defined by the cutoff frequency. Typically, this system utilizes the cutoff frequency phenomenon in waveguides, where rotation is transmitted by an insulated shaft, and unwanted high-frequency noise is effectively blocked by installing a metal housing of a conductive tube that acts as a waveguide at the opening through which the shaft passes. The insulated rotating shaft passes through this housing, and the dimensions of the metal housing are such that the frequency of the unwanted high frequencies is below the cutoff frequency, thereby allowing only rotational force to be transmitted.

[0011] The present invention includes the following embodiments. [1] A rotating shaft device for transmitting rotational force between the inside and outside of a shield wall while blocking high-frequency noise propagating from the inside to the outside or from the outside to the inside of the shield wall, the rotating shaft device comprising a metal tube housing having dimensions that result in a cutoff frequency higher than the frequency of the high-frequency noise to be blocked, and a non-conductive rotating shaft rotatably supported by bearings at both ends of the metal tube housing. [2] The rotating shaft device according to [1], wherein the non-conductive rotating shaft is made of glass fiber reinforced plastic. [3] The rotating shaft device according to [1], wherein the inner diameter of the metal tube housing is 200 mm or less, and the total length of the metal tube housing is 100 mm or more. [4] An anechoic chamber equipped with a rotating shaft device as described in any of [1] to [3]. [5] A rotational force transmission method comprising a waveguide having a cutoff frequency for electromagnetic wave propagation, and a non-conductive rotating shaft that penetrates the waveguide and is rotatably supported at both ends of the waveguide, wherein the dimensions of the waveguide are such that the cutoff frequency is higher than the frequency of the target high-frequency noise, thereby blocking the target high-frequency noise and transmitting only rotational force. [6] The method according to [5], wherein the rotatably supported bearing is provided by a bearing selected with a combination of strength and conductivity such that desired support strength and noise shielding capability are obtained. [Effects of the Invention]

[0012] By using the rotating shaft device of the present invention, electromagnetic waves in the tens of MHz band, which are switching noise generated from the inverter, can be effectively blocked. Therefore, whether the motor under test is operating as the driving side or as the driven side (load), unwanted noise is not propagated through the shaft, which is the means of rotational transmission. This creates a condition where large noises that interfere with the detection of minute noises, such as those required in EMC testing, do not intrude.

[0013] Furthermore, the frequency of the cutoff noise can be adjusted to the desired level by selecting the dimensions and electromagnetic characteristics of the shielding housing tube and the insulator rotating shaft. In other words, by utilizing the phenomenon of cutoff frequency in waveguides, high-frequency noise can be blocked by adjusting the dimensions of the housing tube so that the frequency of the high-frequency noise to be blocked is below the cutoff frequency. [Brief explanation of the drawing]

[0014] [Figure 1] FIG. 1 is a schematic diagram for explaining the basic concept of the present invention. [Figure 2] FIG. 2 is a diagram showing an embodiment of the present invention. [Figure 3] FIG. 3 is a diagram showing a usage example in an anechoic chamber using an embodiment of the present invention.

Mode for Carrying Out the Invention

[0015] FIG. 1 is a schematic diagram of a test facility using a rotating shaft, which is an embodiment of the present invention. The motor 3 and the inverter 4, which are the devices under test installed in the anechoic chamber, rotate the dynamometer 7 and the inverter 6 installed outside the anechoic chamber via the rotating shaft 8 of the present invention, showing a test state. Outside the anechoic chamber, a power supply 9 for driving the device under test motor is installed.

[0016] Inside the anechoic chamber, the measurement antenna 5 measures the electromagnetic wave noise 2 (target noise) generated from the device under test motor 3 and the inverter 4. However, if the electromagnetic wave noise 1 (inverter noise) from the inverter 6 installed outside the anechoic chamber intrudes, the measurement will be impossible or inaccurate. Therefore, it is necessary to completely block the electromagnetic wave noise 1 from outside the anechoic chamber.

[0017] However, since the dynamometer 7 and the device under test motor 3 need to be connected by a rotating shaft 8 for rotational force transmission, the electromagnetic wave noise 1 from the inverter 6 intrudes into the anechoic chamber via the rotating shaft 8. Therefore, it is necessary to make the rotating shaft 8 perform a unique function of blocking electromagnetic wave noise and transmitting rotational motion. For this purpose, the rotating shaft of the present invention is used.

[0018] Figure 2 shows the structure of the rotating shaft of the present invention. In the rotating shaft device of the present invention, a rotating shaft 11 made of an insulator, such as glass fiber reinforced plastic (GFRP), is inserted into a metal tube housing 10 which is a conductive cylinder having a specific inner diameter, and the rotating shaft 11 is supported at both ends of the metal tube housing by bearings 12. Metal flanges and shafts 13 may be provided at both ends of the insulating shaft to connect to the dynamometer 7 and motor 3.

[0019] The metal tube housing 10, which houses the GFRP shaft 11, is a metal tube with an inner diameter of approximately 150 mm. For a metal tube of this size, the cutoff frequency is approximately 1 GHz. Of course, the cutoff frequency will be higher if the inner diameter is smaller. Electromagnetic waves at frequencies lower than the cutoff frequency are attenuated within the waveguide, so if the length is about 200 mm, the electromagnetic waves within the metal tube housing will be attenuated, and unwanted electromagnetic noise, which is the harmonics of the inverter switching noise, can be expected to be attenuated by about 40 dB in the 100-200 MHz band. In other words, with a metal tube housing of about 150 mm inner diameter and 200 mm length, the attenuation is about 100 times greater, so interference can be suppressed to a level that does not affect EMC measurements.

[0020] In this invention, the length of the metal tube housing 10 is sufficient if it blocks or attenuates the electromagnetic noise 1 of the frequency to be attenuated to such an extent that it does not interfere with the measurement. As shown in Figure 2, when placed on a conductive support 14, the noise current 1 escapes to the ground potential, and the electromagnetic noise that passes through the insulator shaft 11 and the internal space of the housing 10 to the other side of the shaft 11 can be reduced to a very large extent.

[0021] Figure 3 shows an example of an EMC testing facility using the rotating shaft device of the present invention. The motor under test 3 is installed in an anechoic chamber, and the rotating shaft device of the present invention is equipped to transmit rotational force.

[0022] The metal tube housing 10 of the rotating shaft device of the present invention is installed penetrating the shield metal wall 15, and the metal tube housing 10 is electrically conductive with the metal of the shield wall 15, and is electromagnetically sealed so that there is no gap between the outer circumference of the metal housing 10 and the shield metal wall 15. Therefore, the only space connecting the inside and outside of the anechoic chamber is the space inside the inner diameter of the metal tube housing 10.

[0023] In the rotating shaft device of the present invention, the GFRP rotating shaft 11, which is an insulator, is rotatably supported by bearings 12 at both ends of the metal tube housing 10. The rotating shaft 11 is provided with flanges at both ends for connecting to the rotating shaft 13 of the motor under test 3 and flanges for connecting to the rotating shaft 13' of the dynamometer outside the anechoic chamber. The bearings 12 that rotatably support the GFRP rotating shaft 11 near both ends inside the metal tube housing 10 may be made of metal balls or ceramic balls, but bearings with ceramic balls are more suitable for more precise EMC testing because they cause less change in impedance due to rotational movement and have a more stable effect in blocking the propagation of electromagnetic waves. As shown in Figure 3, a conductive brush 16 may be further provided to enhance the function of dissipating noise current.

[0024] In the case of the test equipment shown in Figure 3, the largest source of high-frequency noise is the inverter 6 connected to the dynamometer 7. To prevent the high-frequency noise 1 generated from this inverter from leaking into the anechoic chamber, the dimensions of the metal tube housing 10 are determined such that the space connecting the inside and outside of the anechoic chamber, which is the internal space of the metal tube housing 10, is a waveguide whose cutoff frequency can effectively block the main portion of the high-frequency noise.

[0025] As mentioned above, if the inner diameter of the cylindrical metal tube housing 10 is selected to be, for example, 150 mm, the cutoff frequency will be approximately 1 GHz. 1 GHz corresponds to a wavelength of 30 cm. If the length of the metal tube housing is, for example, 200 mm, the electromagnetic waves in the tens of MHz band, which are the high-frequency noise to be blocked, will be attenuated by about 100 times, thus achieving a blocking effect.

[0026] In the rotating shaft device of the present invention, the insulating GFRP shaft that transmits rotational force does not allow high-frequency noise 1 to enter, unlike when a metal shaft is used or when a metal tube housing is not used. Therefore, the high-frequency noise 2 (target noise) to be measured, which is generated from the motor and inverter inside the anechoic chamber that are the equipment to be measured, is generally weaker than the high-frequency noise 1 generated from the inverter 6. If no measures are taken, measurement becomes impossible due to external noise 1 and 1'. However, as shown in Figure 3, by using the rotating shaft of the present invention, inverter noise 1' entering the anechoic chamber can be blocked, so it can be received and detected with sufficient precision by the antenna 5 inside the anechoic chamber without being drowned out.

[0027] The rotating shaft device of the present invention has a unique effect in which mechanical rotational force is transmitted through the shield wall 15, but electromagnetic waves 1 are not transmitted due to the action of a cutoff frequency corresponding to the dimensions of the metal pipe housing 10. Therefore, it can be effectively used to detect weak high-frequency signals in equipment where rotational force transmission is essential during operation, for example, in environments with strong high-frequency noise sources such as motors / inverters for electric vehicles.

[0028] Therefore, since the electromagnetic field environment of an electric vehicle under load conditions that simulate actual driving conditions can be generated in an anechoic chamber without the intrusion of high-frequency noise, it becomes possible to use this technology to measure weak electromagnetic waves from equipment other than the electric vehicle's drive system, without the intrusion of strong high-frequency noise generated by the electric vehicle's drive system, under conditions similar to actual driving conditions.

[0029] The electrical conductivity of the bearings supporting the rotating shaft may be further reduced to improve the insulation between the insulating rotating shaft and all conductors outside the anechoic chamber, thereby further preventing currents excited by electromagnetic noise from leaking through the rotating shaft. To achieve this, instead of supporting the insulating rotating shaft with conventional metal bearings, the insulating rotating shaft may be supported with ball bearings made of highly insulating ceramic balls to prevent high-frequency currents. In other words, the degree of noise suppression and bearing strength are balanced, and the appropriate level of insulation for the bearing can be selected according to the application; the optimal level should be used. [Explanation of symbols]

[0030] 1: Inverter noise 2: Target noise 3: Motor 4: Inverter 5: Antenna 6: Inverter 7: Dynamometer 8: Rotating shaft 9: Power supply 10: Metal pipe housing 11: Shaft 12: Bearings 13: Motor rotation shaft 13': Dynamometer rotation axis 14: Conductive support 15: Shield Wall 16: Conductive brush

Claims

1. A rotating shaft device for transmitting rotational force between the inside and outside of a shield wall while blocking high-frequency noise propagating from the inside to the outside or from the outside to the inside of the shield wall, comprising a metal tube housing having dimensions as a waveguide with a cutoff frequency such that the frequency of the high-frequency noise blocked by the rotating shaft device is higher than the frequency of the high-frequency noise to be blocked, αHz, and a non-conductive rotating shaft rotatably supported by bearings at both ends of the metal tube housing, wherein the frequency to be blocked is αHz, and the rotating shaft device for blocking high-frequency noise.

2. The rotating shaft device according to claim 1, wherein the non-conductive rotating shaft is made of glass fiber reinforced plastic.

3. The rotating shaft device according to claim 1, wherein the inner diameter of the metal tube is 200 mm or less, and the total length of the metal tube is 100 mm or more.

4. An anechoic chamber equipped with a rotating shaft device according to any one of claims 1 to 3.

5. A rotational force transmission method for blocking high-frequency noise of a specific frequency, comprising a waveguide having a cutoff frequency for electromagnetic wave propagation, and a rotating shaft that penetrates the waveguide and is rotatably supported at both ends of the waveguide, wherein the rotating shaft is a non-conductive rotating shaft, and the dimensions of the waveguide are such that the cutoff frequency of the rotational shaft device is higher than the frequency of the specific high-frequency noise to be blocked, thereby blocking the target high-frequency noise and transmitting only rotational force.

6. The method according to claim 5, wherein the rotatable support is performed by a bearing selected with a combination of strength and conductivity such that desired support strength and noise suppression capability are obtained.

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