JP6441624B2 - Casing resonance suppression structure and electric motor - Google Patents

Description

  The present invention relates to a technique for configuring a casing of a prime mover or a transmission and suppressing resonance of a cylindrical casing that is vibrated at a predetermined vibration frequency.

  For example, in a motor as an example of a prime mover, a casing constituting the outer shell of the motor may be vibrated at a predetermined excitation frequency by an electrical signal for controlling the motor and mechanical vibration generated in each part. is there. If such an excitation frequency is a value close to the natural frequency (natural frequency) of the casing, the casing may resonate and become a large noise source. The same problem may occur not only in the casing of the electric motor but also in the casing of a prime mover such as a fluid machine or an internal combustion engine, or in the casing of a transmission such as a speed reducer or a speed increaser.

  In order to solve such a problem, for example, in the noise prevention device for an electric motor described in Patent Document 1, a vibration absorbing mechanism including a washer and a rubber member is provided in a bearing portion disposed in the casing. By providing such a vibration absorbing mechanism, the vibration transmitted to the bearing portion is absorbed and resonance is not induced in the casing.

Japanese Utility Model Publication No. 6-41369

  By the way, when the casing is cylindrical, it is known that a natural mode in which the cross section is deformed into a petal shape occurs remarkably, and it is necessary to particularly suppress resonance in such a natural mode. For this reason, it is conceivable to employ the vibration absorbing mechanism described in Patent Document 1. However, since this requires additional elements such as washers and rubber members, the structure becomes complicated and the assembly is complicated. There was a problem of becoming.

  This invention is made | formed in view of the said subject, and it aims at suppressing the resonance of the cylindrical casing vibrated with a predetermined excitation frequency with a simple structure.

  In order to achieve the above object, a resonance suppression structure for a casing according to the present invention is a resonance suppression structure for a cylindrical casing that forms an outer shell of a prime mover or a transmission and is vibrated at a predetermined excitation frequency. A rib is provided in a part of the casing in the circumferential direction, and among the plurality of natural modes of the casing provided with the rib, the closest to the excitation frequency on the lower frequency side than the excitation frequency The rib is arranged at the position of a node in the natural mode having the natural frequency.

  The cylindrical casing has a plurality of eigenmodes whose cross-section is deformed into a petal shape, and the position of the node differs depending on each mode. As in the present invention, among a plurality of eigenmodes of a casing provided with ribs, an eigenmode having a natural frequency closest to the excitation frequency on the lower frequency side than the excitation frequency (hereinafter referred to as “low-order mode”). In the low-order mode, the influence of the rib on the deformation of the casing is small, and the natural frequency hardly changes compared to the case where no rib is provided. On the other hand, in the eigenmode one higher than the low-order mode across the excitation frequency (hereinafter referred to as “high-order mode”), ribs are arranged at positions other than the nodes. . For this reason, a rib exists in the position where a casing deform | transforms greatly, the substantial rigidity of a casing increases, and the natural frequency of a higher-order mode becomes high compared with the case where a rib is not provided. In other words, the rib is placed at the position of the node of the low-order mode, so that the interval between the natural frequencies of the low-order mode and the high-order mode is widened, and both these natural frequencies are kept away from the excitation frequency. I can leave. That is, according to the present invention, the resonance of the casing can be suppressed with a simple configuration in which ribs are provided in a part of the circumferential direction of the casing.

It is a perspective view which shows the electric motor concerning this embodiment. It is sectional drawing of the casing which shows the circumferential direction position of a rib. It is sectional drawing which shows the deformation | transformation of the casing in tertiary mode. It is sectional drawing which shows the deformation | transformation of the casing in a 4th-order mode. It is sectional drawing which shows typically the position of the rib in a tertiary mode. It is sectional drawing which shows typically the position of the rib in a 4th mode. It is a graph which shows an example of change of a natural frequency of a casing by a rib. It is a conceptual diagram which shows the change of the natural frequency of the casing in 1st Example. It is a conceptual diagram which shows the change of the natural frequency of the casing in 2nd Example. It is a conceptual diagram which shows the change of the natural frequency of the casing in 3rd Example.

  An embodiment in which the casing resonance suppression structure according to the present invention is applied to an electric motor will be described with reference to the drawings.

(Configuration of electric motor)
FIG. 1 is a perspective view showing an electric motor 1 according to the present embodiment. The electric motor 1 is configured such that both ends of the casing 10 are covered with covers 11 and 12 in a state where a stator and a rotor (not shown) are accommodated in a cylindrical casing 10. The cover 11 is provided with a bearing 13, and a rotating shaft 14 rotatably supported by the bearing 13 protrudes upward in the figure from the cover 11.

  A plurality of ribs 15 extending along the circumferential direction are provided on the outer peripheral surface of the casing 10. FIG. 2 is a sectional view of the casing 10 showing the circumferential position of the rib 15. As shown in FIG. 2, the ribs 15 are provided at regular intervals every 60 degrees in the circumferential direction, and a total of six ribs 15 are arranged on the entire circumference. As shown in FIG. 1, two rows of six ribs 15 are provided in the axial direction of the casing 10 so as to be in the same position in the circumferential direction. The principle that the resonance of the casing 10 is suppressed by the rib 15 will be described in detail later.

(Case deformation in each eigenmode)
The cylindrical casing 10 has a plurality of natural modes in which a cross section orthogonal to the axial direction is deformed into a petal shape. As an example, the deformation of the casing 10 in the third-order eigenmode (hereinafter referred to as “third-order mode”) is illustrated in FIG. 3A, and the fourth-order eigenmode (hereinafter referred to as “fourth-order mode”) in FIG. The deformation of the casing 10 is shown in cross-sectional views orthogonal to the axial direction. In FIGS. 3A and 3B, the position of the casing 10 that is not deformed is indicated by a broken line. The rib 15 is not shown.

  As shown in FIG. 3A, in the third-order mode, the nodes 10a that are hardly displaced appear at regular intervals every 60 degrees in the circumferential direction. The middle part of the adjacent nodes 10a is a so-called “belly”, which is the part with the largest amplitude. On the other hand, as shown in FIG. 3B, in the fourth-order mode, the nodes 10b that hardly displace appear at regular intervals every 45 degrees in the circumferential direction. The middle part of the adjacent nodes 10b is a so-called “belly”, which is the part with the largest amplitude. In this way, the position of the node varies depending on the order of the eigenmode. In the present embodiment, ribs 15 are arranged at each position of the node 10a in the tertiary mode.

(Change in casing natural frequency due to ribs)
4A is a cross-sectional view schematically showing the position of the rib 15 in the third-order mode, and FIG. 4B is a cross-sectional view schematically showing the position of the rib 15 in the fourth-order mode. In FIGS. 4A and 4B, the rib 15 is indicated by a thick line, and the position of the casing 10 in an undeformed state is indicated by a broken line.

  The rib 15 is provided at each position of the six nodes 10a in the tertiary mode. For this reason, as is apparent from FIG. 4A, in the third-order mode, the rib 15 is originally provided in a portion that is hardly displaced (a portion in the vicinity of the node 10a). The rigidity of 10 is hardly increased. As a result, before and after the rib 15 is provided, the natural frequency (natural frequency) in the third-order mode hardly changes.

  On the other hand, the position of the node 10b in the fourth-order mode is different from the position of the node 10a in the third-order mode. For this reason, the ribs 15 arranged at the respective positions of the nodes 10a in the third-order mode are also present in the parts where the displacement is large in the fourth-order mode (parts other than the nodes 10b in the fourth-order mode) as is clear from FIG. It will be provided. As a result, in the fourth-order mode, the provision of the rib 15 increases the substantial rigidity of the casing 10 and significantly increases the natural frequency.

  FIG. 5 is a graph showing an example of changes in the natural frequency of the casing 10 due to the ribs 15. Specifically, it is a graph showing the result of calculating the vibration speed response before and after providing the rib 15 at each position of the node 10a in the tertiary mode. As is apparent from this result, when the rib 15 is provided at the position of the node 10a in the third-order mode, the natural frequency of the third-order mode hardly changes, but the natural frequency of the fourth-order mode is significantly increased. As a result, the interval between the natural frequencies of the third-order mode and the fourth-order mode is widened. Each embodiment described below uses such a change in the natural frequency of the casing 10 due to the ribs 15 to suppress the resonance of the casing 10.

(First embodiment)
FIG. 6 is a conceptual diagram showing changes in the natural frequency of the casing 10 in the first embodiment, where the thin line indicates the vibration response of the casing 10 before the rib 15 is provided, and the thick line indicates the casing 10 after the rib 15 is provided. The vibration response is shown. In each embodiment described here, the carrier frequency is cited as an example of the excitation frequency input to the casing 10. The carrier frequency is a frequency of a modulation wave for determining a pulse width of an output current (voltage) by an inverter (not shown) when the motor 1 is controlled by PWM (Pulse Width Modulation). It is known that when the casing 10 has a natural frequency close to the carrier frequency, the casing 10 resonates and high-frequency noise is generated.

  First, mode analysis by numerical calculation or experiment is performed on the casing 10 without the ribs 15. By executing the mode analysis, it is possible to grasp the natural frequencies and the positions of the nodes in the plurality of natural modes of the casing 10. As a result, in the first embodiment, as shown by the thin line in FIG. 6, the third-order mode and the fourth-order mode exist so as to sandwich the carrier frequency, and the natural frequency of the fourth-order mode is closest to the carrier frequency. It is intended for cases with values.

  In such a case, by providing the rib 15 at the position of the node 10a in the third-order mode, the natural frequency of the third-order mode is hardly changed, and the natural frequency of the fourth-order mode can be significantly increased. As a result, as shown by the thick line in FIG. 6, the interval between the natural frequencies of the third-order mode and the fourth-order mode is widened, and the natural frequencies of both modes are sufficiently separated from the carrier frequency. Therefore, resonance of the casing 10 can be suppressed.

  As in the first embodiment, among the plurality of eigenmodes of the casing 10 before the rib 15 is provided, the fourth-order mode having the eigenfrequency closest to the carrier frequency on the higher frequency side than the carrier frequency is higher than the carrier frequency. In the case of having a natural frequency closer to the carrier frequency than the tertiary mode having the natural frequency closest to the carrier frequency on the low frequency side, by providing the rib 15 at the position of the node 10a in the tertiary mode, It is possible to suppress resonance.

(Second embodiment)
The second embodiment has a step of reducing the overall thickness of the casing 10 before providing the rib 15. FIG. 7 is a conceptual diagram showing changes in the natural frequency of the casing 10 in the second embodiment, in which the thin line indicates the vibration response of the casing 10 before the plate thickness is reduced and before the rib 15 is provided, and the broken line indicates the plate thickness. The thin line shows the vibration response of the casing 10 after the thickness is reduced and before the rib 15 is provided, and the thick line shows the vibration response of the casing 10 after the thickness is reduced and the rib 15 is provided.

  In the second embodiment, as a result of the mode analysis, as shown by the thin line in FIG. 7, the third mode and the fourth mode exist so as to sandwich the carrier frequency, and the natural frequency of the third mode becomes the carrier frequency. The case with the closest value is targeted. In such a case, as in the first embodiment, if the rib 15 is provided at the position of the node 10a in the third-order mode, the natural frequency of the third-order mode remains close to the carrier frequency, and the resonance of the casing 10 is avoided. Can not do it.

  Therefore, in such a case, by reducing the overall thickness of the casing 10 and reducing the rigidity of the casing 10 as a whole, as shown by the broken lines in FIG. Reduce the natural frequency at. Thus, after the natural frequency of the third-order mode is moved away from the carrier frequency, the natural frequency of the third-order mode is hardly changed by providing the rib 15 at the position of the node 10a in the third-order mode. Can be significantly increased. As a result, as shown by the thick line in FIG. 7, the interval between the natural frequencies of the third-order mode and the fourth-order mode is widened, and the natural frequencies of both modes are sufficiently separated from the carrier frequency. Therefore, resonance of the casing 10 can be suppressed.

  Of the plurality of eigenmodes of the casing 10 before the rib 15 is provided as in the second embodiment, the third-order mode having the eigenfrequency closest to the carrier frequency on the lower frequency side than the carrier frequency is the carrier frequency. When the natural frequency is closer to the carrier frequency than the fourth-order mode having the natural frequency closest to the carrier frequency on the higher frequency side, the plate thickness of the casing 10 is reduced as a whole to increase the rigidity of the casing 10 as a whole. After being reduced in size, resonance of the casing 10 can be suppressed by providing the rib 15 at the position of the node 10a in the tertiary mode. As a method of reducing the overall rigidity of the casing 10, it is also effective to change the material of the casing 10 to one having a small elastic modulus instead of reducing the plate thickness.

(Third embodiment)
FIG. 8 is a conceptual diagram showing changes in the natural frequency of the casing 10 in the third embodiment, where the thin line indicates the vibration response of the casing 10 before the rib 15 is provided, and the thick line indicates the casing 10 after the rib 15 is provided. The vibration response is shown. In the third embodiment, as a result of the mode analysis, as shown by a thin line in FIG. 8, the fourth and fifth modes exist so as to sandwich the carrier frequency, and the natural frequency of the fourth order mode becomes the carrier frequency. This is for cases where the values are close.

  In such a case, as in the second embodiment, the ribs may be provided at the nodes of the quaternary mode after the overall rigidity of the casing 10 is once lowered. However, in the third embodiment, the rib 15 is provided at the position of the node 10a in the third-order mode that is one order lower than the fourth-order mode that is known to be closest to the carrier frequency before the rib 15 is provided. The resonance of the casing 10 is avoided.

  By providing the rib 15 at the position of the node 10a in the third-order mode, the natural frequency of the third-order mode is hardly changed, and the natural frequency of the fourth-order mode can be significantly increased. As a result, as shown by the thick line in FIG. 8, the interval between the natural frequencies of the third-order mode and the fourth-order mode is widened, and the natural frequencies of both modes are sufficiently separated from the carrier frequency. Therefore, resonance of the casing 10 can be suppressed.

  Of the plurality of eigenmodes of the casing 10 before the rib 15 is provided as in the third embodiment, the fourth-order mode having the eigenfrequency closest to the carrier frequency on the lower frequency side than the carrier frequency is the carrier frequency. In the case of having the natural frequency closer to the carrier frequency than the fifth order mode having the natural frequency closest to the carrier frequency on the higher frequency side, the node 10a in the third order mode which is one order lower than the fourth order mode. By providing the rib 15 at the position, resonance of the casing 10 can be suppressed.

(effect)
As described above, in any of the embodiments, as a result, among the plurality of eigenmodes of the casing 10 provided with the rib 15, the eigenmode has a natural frequency closest to the carrier frequency on the lower frequency side than the carrier frequency. The rib 15 is provided at the position of the node 10a in the tertiary mode (low-order mode). Thus, when the rib 15 is provided at the position of the node 10a in the third-order mode, the influence of the rib 15 on the deformation of the casing 10 is small in the third-order mode, and the natural frequency is smaller than the case where the rib 15 is not provided. Almost no change. On the other hand, in the fourth-order mode (higher-order mode) that is one higher than the third-order mode across the carrier frequency, the ribs 15 are arranged at positions other than the node 10b. For this reason, the rib 15 exists in the position which the casing 10 deform | transforms greatly, the substantial rigidity of the casing 10 increases, and the natural frequency of a 4th-order mode becomes high compared with the case where the rib 15 is not provided. In other words, the rib 15 is arranged at the position of the node 10a of the third-order mode, so that the interval between the natural frequencies of the third-order mode and the fourth-order mode is widened, and both these natural frequencies are kept away from the carrier frequency. Can do. That is, according to the present embodiment, resonance of the casing 10 can be suppressed with a simple configuration in which ribs are provided in a part of the circumferential direction of the casing 10.

  In addition, when the rib which continues over the perimeter of the casing 10 is provided, the rigidity of the casing 10 increases as a whole, the natural frequency increases in both the third-order mode and the fourth-order mode, and the interval between the natural frequencies of both modes is increased. It will not spread. That is, in order to obtain the above-described effect, it is important that the ribs 15 are provided only in a part of the casing 10 in the circumferential direction.

  In the present embodiment, the ribs 15 are provided for at least two or more of the plurality of nodes 10a existing in the tertiary mode. For this reason, the substantial rigidity of the casing 10 in the fourth-order mode is further increased, and the interval between the natural frequencies of the third-order mode and the fourth-order mode can be further increased, so that the resonance of the casing 10 can be reliably suppressed. it can. In particular, by providing the ribs 15 for all of the plurality of nodes 10a as in the present embodiment, such an effect becomes more remarkable.

  In the present embodiment, a plurality of ribs 15 are also provided in the axial direction of the casing 10. For this reason, the substantial rigidity of the casing 10 in the fourth-order mode is further increased, and the interval between the natural frequencies of the third-order mode and the fourth-order mode can be further increased, so that the resonance of the casing 10 can be reliably suppressed. it can.

(Other embodiments)
The present invention is not limited to the above embodiment, and the elements of the above embodiment can be appropriately combined or variously modified without departing from the spirit of the present invention.

  For example, in the above embodiment, the case where the resonance suppression structure of the casing according to the present invention is applied to the electric motor 1 has been described. However, the resonance suppression structure may be a fluid machine (for example, a pump) or an internal combustion engine (for example, an engine). The present invention can also be applied to a casing of a prime mover or a casing of a transmission such as a speed reducer or a speed increaser.

  In addition, the excitation frequency in the present invention is not limited to the carrier frequency, and the frequency of the excitation force input to the casing 10 by mechanical vibration may be used as the excitation frequency. For example, regarding the electric motor, in addition to the carrier frequency, the motor frequency (number of revolutions × number of poles, number of revolutions × number of slots) may be used as the excitation frequency. Similarly, in the case of a pump, the number of revolutions of the pump (the number of revolutions × the number of cylinders), in the case of an engine, the engine explosion order (the number of revolutions × the number of cylinders / 2), and in the case of a transmission, the gear meshing frequency (the number of revolutions × the number of teeth). The number) can be set as the excitation frequency.

  In the above embodiment, the casing 10 is cylindrical. However, the shape of the casing 10 is not limited to a cylindrical shape as long as it is cylindrical, and the cross-sectional shape may be a polygon or the like.

1: Electric motor
10: Casing 10a: Node 15: Rib

Claims (6)

Resonance suppression structure of a cylindrical casing that constitutes the outer shell of the prime mover or the transmission and is vibrated at a predetermined vibration frequency,
Ribs are provided in part of the circumferential direction of the casing,
Among the plurality of eigenmodes of the casing provided with the rib, the position of the node in the low-order mode which is the eigenmode having the eigenmode closest to the excitation frequency on the lower frequency side than the excitation frequency And the ribs are arranged ,
A resonance suppression structure for a casing , wherein a natural frequency of one higher-order eigenmode than the lower-order mode is greater than the excitation frequency .   2. The casing resonance suppression structure according to claim 1, wherein there are a plurality of the nodes, and the ribs are provided for at least two of the plurality of nodes. 3.   The resonance suppression structure for a casing according to claim 2, wherein the rib is provided for all of the plurality of nodes.   4. The casing resonance suppression structure according to claim 1, wherein a plurality of the ribs are provided in an axial direction of the casing. 5.   5. The casing resonance suppression structure according to claim 1, wherein the excitation frequency is a carrier frequency when the motor as the prime mover is subjected to PWM control. 6.   An electric motor having the casing resonance suppression structure according to claim 5.

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