Housing for accommodating electric circuit

Abstract

This housing for accommodating an electric circuit has a case that accommodates an electric circuit, and a cover that closes an opening of the case. The cover has a first region part that contacts the case, a second region part that is arranged on the inner-peripheral side of the first region part in a plane, a third region part that connects the first region part and the second region part, and a reinforcement part that extends on the third region part and is connected to the second region part. The mass per unit area of the second region part is greater than that of the third region part as seen from a direction in which the cover is attached to the case. The third region part has a fourth region part and a fifth region part adjacent to the second region part on the inner-peripheral side of the fourth region. The reinforcing part has a notch at a position excluding the distal-end part in the extension direction. The fifth region part forms an angle greater than 45 degrees with respect to the second region part in a cross-section, or the ratio of the radius of curvature to the height of the second region part is greater than 1, so that the mass per unit area increases toward the inner-peripheral side as seen from the direction in which the cover is attached to the case.

Description

Electrical circuit housing

[0001] The present invention relates to an enclosure for housing an electric circuit.

[0002] Drive units for electric vehicles are required to be smaller, lighter, and quieter for comfort. Accordingly, the housings of each part of the drive unit tend to be thinner. Furthermore, inverter covers, which are flat components, tend to vibrate more than the housings of motors and reducers.

[0003] As a measure to suppress radiated sound from a housing due to the propagation of vibration, for example, Patent Document 1 discloses a configuration having a case that houses electronic components and a cover that covers the opening of the case, the cover having a weight portion near the center and a rib that connects to the weight portion, with notches in the rib that increase the rigidity of parts other than the weight portion, and the notches that reduce the rigidity near the weight portion, concentrating the antinode of the primary vibration of the membrane surface of the cover at the center of the weight portion, thereby increasing the vibration reduction effect of the weight portion.

[0004] Japanese Patent Application Laid-Open No. 2021-190563

[0005] The technology described in Patent Document 1 has a problem in that the secondary vibration of the membrane surface is aggravated by the concentration of stress at the intersection of the second and third regions, and the rigidity of the cover is unbalanced. In view of this, an object of the present invention is to provide a housing for an electric circuit that prevents the aggravation of the secondary vibration of the membrane surface.

[0006] The housing for an electric circuit comprises a case that houses the electric circuit and a cover that closes an opening of the case, the cover having a first region that contacts the case, a second region that is positioned more inward than the first region in a plan view, a third region that connects the first region and the second region, and a reinforcing portion that extends on the third region and is connected to the second region, the second region having a mass per unit area greater than that of the third region when viewed from the direction in which the cover is attached to the case, the third region having a fourth region and a fifth region that is more inward than the fourth region and adjacent to the second region, the reinforcing portion having a notch at a position in the extension direction excluding the tip, the fifth region forming an angle greater than 45 degrees with respect to the second region in cross section or the ratio of the radius of curvature to the height of the second region is greater than 1 so that the mass per unit area increases toward the inner side when viewed from the direction in which the cover is attached to the case.

[0007] According to the present invention, it is possible to provide a housing for an electric circuit that prevents deterioration of the secondary vibration of the membrane surface.

[0008] FIG. 1 is a cross-sectional view of an entire drive unit according to a first embodiment of the present invention; FIG. 2 is a cross-sectional view of an entire drive unit according to a first embodiment of the present invention; FIG. 3 is a cross-sectional view of an entire drive unit according to a first embodiment of the present invention; FIG. 4 is a cross-sectional view of an entire drive unit according to a first embodiment of the present invention; FIG. 5 is a cross-sectional view of an entire drive unit according to a first embodiment of the present invention;

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following description and drawings are examples for explaining the present invention, and some omissions and simplifications have been made as appropriate for clarity of explanation. The present invention can be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.

[0010] In order to facilitate understanding of the invention, the position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[0011] (First embodiment and overall configuration) (FIGS. 1 and 2) The drive unit 1 is used as a drive source for an electrically powered vehicle such as an electric vehicle or a hybrid vehicle, and is mounted on the vehicle. The drive unit 1 includes an inverter 2, a motor 3, and a reduction gear 4. The motor 3 and the reduction gear 4 are connected to each other. A drive shaft (not shown) that drives a tire (not shown) is connected to the end of an output shaft 41 of the drive unit 1.

[0012] The inverter 2 is connected to the motor 3. The motor 3 has a rotor 31 and a stator 32 in a motor housing 30. The motor 3 vibrates due to an electromagnetic excitation force generated in the gap between the rotor 31 and the stator 32 when driven, and therefore serves as a vibration source for the drive unit 1.

[0013] The reducer 4 converts the rotational speed and torque of the motor 3 and transmits them to the drive shaft. The inverter 2 converts DC power from a battery or the like (not shown) into AC power and supplies it to the motor 3, controlling the power supply to the motor 3. The drive unit 1 generates a driving torque or a braking torque for the motor 3 based on commands received from the inverter 2.

[0014] The inverter 2 includes a circuit board 20, which is an electric circuit for controlling power, and a case 21 that houses the circuit board 20. The circuit board 20 has various electronic components (not shown) mounted thereon. The case 21 has, for example, an opening for housing the circuit board 20 therein and a housing space 21a that houses the circuit board 20 through the opening. The case 21 is also provided with a removable cover 22 that closes the opening of the case 21.

[0015] The case 21 has a bottom 21b attached to the motor housing 30, a side wall 21c extending from the outer periphery of the bottom 21b, and an annular flange 21d that functions as an attachment portion for attaching the cover 22. The case 21 is fastened to the motor housing 30 with bolts. The outer periphery of the cover 22 is fastened to the flange 21d of the case 21 with bolts.

[0016] Vibrations caused when the drive unit 1 is driven are transmitted to the motor housing 30, the gear case 40, and the case 21 and cover 22 of the inverter 2. Specifically, vibrations caused by the electromagnetic excitation force generated between the stator 32 and the rotor 31 and the gear meshing excitation force are transmitted to the motor housing 30 and the gear case 40, and then transmitted to the case 21 and cover 22 of the inverter 2 via the connection between the motor housing 30 and the inverter 2.

[0017] The cover 22 is generally a flat plate-shaped member, and therefore has lower rigidity and is more susceptible to vibration than other members such as the motor housing 30 and the gear case 40. In particular, the lower the vibration mode, the greater the vibration tends to be, and the greater the radiated sound caused by the vibration of the cover 22 tends to be.

[0018] (FIGS. 3 to 5) The cover 22 has a basic structure of a plate-like portion that closes the opening of the case 21. The cover 22 has an annular first region 22a that contacts the flange portion 21d (FIG. 2) of the case 21, a second region 22b that is a heavy portion located more inward than the first region 22a in a plan view, and a third region 22c that is provided between the first region 22a and the second region 22b and connects the first region 22a and the second region 22b. The cover 22 is formed by integrally molding the first region 22a, the second region 22b, and the third region 22c.

[0019] The third region 22c has a fourth region 22d and a fifth region 22e that is located on the inner circumferential side of the fourth region 22d and adjacent to the second region 22b.

[0020] The first region 22a forms the outer periphery of the cover 22. The surface of the first region 22a on the lower side in FIG. 4 comes into contact with the flange 21d of the case 21. The first region 22a is fastened to the flange 21d of the case 21 with bolts, thereby increasing the rigidity.

[0021] The second region 22b has a mass (weight) per unit area that is relatively larger than that of the third region 22c when viewed from the mounting direction D, which is the direction in which the cover 22 is mounted to the case 21. As shown in Fig. 4, the second region 22b is thicker than the third region 22c and bulges outward from the cover 22 more than the third region 22c in cross section.

[0022] The second region 22b is located approximately in the center of the cover 22 when viewed from the direction D in which the cover 22 is attached to the case 21. As shown by the movement 5a of the primary membrane vibration of the cover 22, the antinode (the position of maximum amplitude) of the primary membrane vibration is included within the range of the second region 22b. In other words, the primary membrane vibration of the cover 22 is a vibration mode in which the antinode is located approximately in the center of the cover 22 when viewed from the direction D in which the cover 22 is attached to the case 21. The second region 22b is molded integrally with the third region 22c.

[0023] Ribs 23, which increase the rigidity of the third region 22c, extend from the four corners of the case 21 to connect to the second region 22b on the third region 22c. The ribs 23 are reinforcing members provided on the outer surface of the third region 22c. As shown in FIG. 3, four ribs 23 are provided on the outer surface of the cross section of the third region 22c, and are molded from the second region 22b toward the bolts provided at the four corners of the first region 22a. The ribs 23 are, for example, molded integrally with the second region 22b and the third region 22c.

[0024] The rib 23 has notches 23a at positions other than the four corners of the third region 22c, which is the tip end in the extension direction. The notches 23a are formed from any position on the rib 23 along the extension direction to a position reaching the second region 22b.

[0025] The shape of the rib 23, such as its length, width (thickness), and height, as well as the position, length, and depth of the notch 23a, are taken into consideration so that the position of the antinode of the primary vibration of the membrane surface of the cover 22 is set within the range of the second area portion 22b.

[0026] The shapes of the ribs 23 and the notches 23a are set so as to prevent the natural frequency of the primary vibration of the membrane surface of the cover 22 from falling within the range of the natural frequencies of other members such as the case 21, or the frequency range where human hearing is highly sensitive (for example, a range from 1 kHz to 4 kHz). In other words, by adjusting various parameters of the ribs 23 and the notches 23a, the positions of the antinodes of the primary vibration of the membrane surface of the cover 22 can be adjusted, and the natural frequency of the primary vibration of the membrane surface of the cover 22 can be set within a frequency range within a predetermined range.

[0027] The fifth region 22e forms an arbitrary inclination angle θ on the cross section so that the mass per unit area increases toward the inner periphery when viewed from the attachment direction D of the cover 22 to the case 21. The fifth region 22e connects the second region 22b and the fourth region 22d.

[0028] As shown in Figure 5, when viewed from the mounting direction D, the secondary membrane vibration that vibrates like the secondary membrane vibration movement 5b has a vibration node (a position where the amplitude is 0) at approximately the center of the second region 22b in the horizontal or vertical direction in a plan view. In other words, the center portion between the boundary between the fourth region 22d and the first region 22a and the node position becomes the antinode of the secondary membrane vibration. The secondary membrane vibration is a vibration mode that vibrates in antiphase with the node as a boundary.

[0029] By providing the fifth region 22e around the second region 22b, stress is not concentrated near the antinode of the membrane surface secondary vibration, thereby preventing the deterioration of the membrane surface secondary vibration. Furthermore, by providing the fifth region 22e, the rigidity balance of the cover 22 is not changed with respect to the membrane surface primary vibration, so the antinode of the membrane surface primary vibration can be maintained approximately in the center of the second region 22b. Therefore, the membrane surface primary vibration can be reduced while suppressing the deterioration of the membrane surface secondary vibration.

[0030] (Fig. 6) The inclination angle θ of the fifth region 22e (Fig. 5), which is effective in reducing the secondary vibration of the membrane surface, will be described. Note that the horizontal axis of Fig. 6 indicates the inclination angle θ of the fifth region 22e, and the vertical axis indicates the weight-to-effectiveness ratio for reducing the secondary vibration of the membrane surface. Note that the base showing the reduction amount on the vertical axis is shaped without the fifth region 22e.

[0031] As the inclination angle θ increases, the weight-to-effectiveness ratio of the membrane secondary vibration reduction increases when the angle exceeds 45 degrees, and converges at an inclination angle of approximately 60 degrees. This is because, from a state in which force is concentrated near the antinode of the membrane secondary vibration (the intersection of the second region 22b and the fourth region 22d), as the inclination angle θ increases, the force concentration is gradually released and converges at an inclination angle of 60 degrees. Therefore, the inclination angle θ may be set to an angle greater than 45 degrees, for example. Furthermore, by setting the inclination angle θ to 60 degrees or more, the weight-to-effectiveness ratio for the reduction of the membrane secondary vibration is maximized.

[0032] (Second embodiment) (Figures 7 and 8) The fifth region 22e does not need to form the inclination angle θ as described above, but as long as it has a radius of curvature r whose ratio to the height h of the second region 22b is greater than 1, as shown in Figure 8, a similar effect can be obtained.

[0033] (Fig. 9) The radius of curvature r of the fifth region 22e, which is effective in reducing the secondary vibration of the membrane surface shown in Fig. 8, will be explained. The horizontal axis of Fig. 9 represents the ratio (r / h) of the radius of curvature r of the fifth region 22e to the height h of the second region 22b, and the vertical axis represents the weight-to-effectiveness of reducing the secondary vibration of the membrane surface. Note that the base showing the amount of reduction on the vertical axis is a shape that does not include the fifth region 22e.

[0034] The weight-to-benefit ratio increases when the ratio of the radius of curvature r of the fifth region 22e to the height h of the second region 22b exceeds 1, and the effect converges to a maximum when the ratio of the radius of curvature r is 2.3. The mechanism is the same as in the first embodiment. Therefore, in the second embodiment, the weight-to-benefit ratio for reducing the secondary membrane vibration is maximized by making the radius of curvature r of the fifth region 22e, for example, greater than 2.3 times the height h of the second region 22b.

[0035] In the present invention, the ribs 23 may be provided anywhere in the third region 22c, and the number and shape of the ribs are not limited. Furthermore, the second region 22b and the fifth region 22e may be provided not only on the outside but also on the inside of the space formed by the cover 22 and the case 21. The fifth region 22e may be provided on the top surface of the second region 22b rather than on the side surface, or on the side surface midway along the height of the second region 22b. The fifth region 22e may extend over the entire outer periphery of the second region 22b or a part of it. This configuration may be provided not only in the drive unit including the inverter, motor, and reducer illustrated in this embodiment, but also in a housing structure for an electrical circuit in another device, such as a motor generator.

[0036] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0037] (1) The housing for an electric circuit includes a case 21 that houses the electric circuit and a cover 22 that closes an opening of the case 21. The cover 22 includes a first region 22a that contacts the case 21, a second region 22b that is disposed on the inner periphery side of the first region 22a in a plan view, a third region 22c that connects the first region 22a and the second region 22b, and a reinforcing portion 23 that extends on the third region 22c and is connected to the second region 22b. When viewed from the direction in which the cover 22 is attached to the case 21, the second region 22b has a mass per unit area that is larger than that of the third region. The third region 22c is larger than the third region 22c, and the third region 22c has a fourth region 22d and a fifth region 22e adjacent to the second region 22b on the inner circumferential side of the fourth region 22d, and the reinforcing portion 23 has a notch 23a at a position in the extension direction excluding the tip end, and the fifth region 22e forms an angle of more than 45 degrees with respect to the second region 22b on the cross section when viewed from the direction in which the cover 22 is attached to the case 21, or the ratio of the radius of curvature to the height of the second region 22b is greater than 1, so that the mass per unit area increases toward the inner circumferential side. In this way, it is possible to provide a housing for an electric circuit that prevents deterioration of the secondary vibration of the membrane surface.

[0038] (2) The fifth region 22e forms an angle of more than 60 degrees with respect to the second region 22b on the cross section, or the ratio of the radius of curvature to the height of the second region 22b is more than 2.3. This maximizes the weight-to-effectiveness ratio for reducing the secondary vibration of the membrane surface.

[0039] The present invention is not limited to the above-described embodiments, and various modifications and combinations of other configurations are possible without departing from the spirit of the present invention. Furthermore, the present invention is not limited to those having all of the configurations described in the above-described embodiments, and includes those in which some of the configurations are omitted.

[0040] REFERENCE SIGNS LIST 1 Drive device 2 Inverter 3 Motor 4 Reducer 5a Movement of membrane surface primary vibration 5b Movement of membrane surface secondary vibration 20 Circuit board 21 Case 21a Storage space 21b Bottom 21c Side wall 21d Flange 22 Cover 22a First region 22b Second region 22c Third region 22d Fourth region 22e Fifth region 23 Rib 23a Notch 30 Motor housing 31 Rotor 32 Stator 40 Gear case 41 Output shaft

Claims

1. A device comprising a case that houses an electric circuit and a cover that closes an opening of the case, the cover having a first region that contacts the case, a second region that is located on the inner periphery side of the first region in a plan view, a third region that connects the first region and the second region, and a reinforcing portion that extends on the third region and is connected to the second region, the second region having a mass per unit area greater than that of the third region when viewed from a direction in which the cover is attached to the case, the third region having a fourth region and a fifth region that is adjacent to the second region on the inner periphery side of the fourth region, the reinforcing portion having a notch at a position excluding a tip portion in the extension direction, the fifth region forming an angle of greater than 45 degrees with respect to the second region on a cross section so that the mass per unit area increases toward the inner periphery when viewed from a direction in which the cover is attached to the case, or the ratio of the radius of curvature to the height of the second region is greater than 1 An enclosure that contains electrical circuits.

2. An electric circuit housing according to claim 1, wherein the fifth region forms an angle of greater than 60 degrees with respect to the second region on a cross section, or the ratio of the radius of curvature to the height of the second region is greater than 2.3.

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