case

Abstract

The goal is to reduce noise generated in the case housing the vibration source while suppressing an increase in physical size. [Solution] The case 1 housing the vibration source 2 comprises a case body 3 that forms the outer shape and a covering member 4 that covers at least a part of the outer surface 3a of the case body 3. The covering member 4 comprises a plurality of covering layers 6, and the acoustic impedance of the innermost covering layer 5, which is the covering layer 6 located on the innermost Xb, is lower than the acoustic impedance of the case body 3 and lower than the acoustic impedance of the covering layer 6 in contact with the outer surface 5a of the innermost covering layer 5.

Description

Technical Field

[0006] , , ,

[0005] ,

[0001] The present invention relates to a case for housing a vibration source.

Background Art

[0002] For example, in a hybrid vehicle or an electric vehicle, a rotating electric machine that serves as a driving force source for wheels may generate vibrations during driving, which can be a source of noise for passengers in the vehicle cabin. To improve the quietness in the vehicle cabin, for example, Japanese Patent Application Laid-Open No. 2021-170086 proposes covering the entire driving device (rotating electric machine), which is a vibration source, with a soundproof cover (10). (In the background art, the reference numerals in parentheses refer to those in the cited document.) The soundproof cover (10) is configured such that two cover portions (11, 12) are connected by a hinge portion (13) so as to be openable and closable, and when the hinge portion (13) is closed, the two cover portions (11, 12) cover the entire outer surface of the case of the driving device (rotating electric machine). The cover portion (11, 12) is configured to include a surface layer (1), a sound insulation layer (2), and a sound absorption layer (3).

Prior Art Documents

Patent Documents

[0007] With this configuration, vibrations transmitted from the vibration source to the outside of the case are reflected back towards the vibration source at the boundaries between parts with different acoustic impedances: the boundary between the case body and the innermost covering layer, and the boundary between the covering layer in contact with the outer surface of the innermost covering layer and the innermost covering layer. This reduces the vibrations transmitted to the outside of the case. Because the boundaries are utilized, the thickness of each covering layer does not need to be considered, making it easier to keep the thickness of the covering material down and preventing the case from becoming larger. In other words, this configuration makes it possible to reduce noise generated in the case housing the vibration source while suppressing an increase in size.

[0008] Further features and advantages of the case will become clear from the following description of exemplary and non-limiting embodiments, which will be illustrated with reference to the drawings. [Brief explanation of the drawing]

[0009] [Figure 1] Schematic perspective view of a vehicle drive system [Figure 2] Schematic cross-sectional view of a vehicle drive system [Figure 3] A schematic enlarged cross-sectional view showing the first example of a covering member. [Figure 4] A schematic enlarged cross-sectional view showing a second example of the covering member. [Figure 5] A schematic enlarged cross-sectional view showing a third example of the covering member. [Figure 6] A schematic enlarged cross-sectional view showing a fourth example of the covering member. [Modes for carrying out the invention]

[0010] The following describes an embodiment of the case housing the vibration source with reference to the drawings. In this embodiment, the vibration source is a rotating electric machine 2, here an example of a traction motor (which also functions as a generator) that serves as the driving force source for the wheels in a vehicle. However, the rotating electric machine 2 may be a motor that serves as the driving force source for the compressor in an on-board air conditioner, or a motor that serves as the driving force source for an on-board oil pump or water pump. Furthermore, the vibration source may consist only of the rotating electric machine 2, or it may include the rotating electric machine 2 and a power transmission mechanism (such as a gear mechanism) that transmits power to the rotating electric machine 2. Moreover, it is not prohibited to have a configuration in which only the gear mechanism is the vibration source, a configuration in which an internal combustion engine is the vibration source, or a configuration in which various other machines are the vibration source.

[0011] Figure 1 is a schematic perspective view of a vehicle drive system 10, including a rotating electric machine 2 as a traction motor. Figure 2 shows a schematic cross-sectional view perpendicular to the axis of the vehicle drive system 10. The vehicle drive system 10 comprises a first housing chamber 11 inside the case 1, which houses the rotating electric machine 2 and a power transmission mechanism (gear mechanism, etc.), and a second housing chamber 12, which houses the rotating electric machine drive system 20, which is an electrical circuit that drives the rotating electric machine 2. At least the first housing chamber 11 is formed inside the case body 3.

[0012] The rotating electric machine 2, which is the driving force source for the wheels, may generate noise for occupants inside the vehicle cabin due to vibrations during operation. Specifically, vibrations from the rotating electric machine 2, which is the vibration source, may be transmitted to the case body 3, causing the case body 3 to vibrate and generate audible noise. To suppress such noise, in this embodiment, a covering member 4 is provided that covers at least a part of the outer surface of the case body 3, which constitutes the outer shape of the case 1. Since vibrations that propagate from the first housing chamber 11 through the second housing chamber 12 to the outside of the case 1 may be attenuated by the second housing chamber 12, Figure 2 illustrates a configuration in which the covering member 4 is provided on the case body 3 so as to cover the first housing chamber 11. However, the covering member 4 may also be provided so as to cover the entire case 1, including the second housing chamber 12.

[0013] As shown in Figure 2, the covering member 4 comprises multiple covering layers 6. Furthermore, the acoustic impedance of the innermost covering layer 5, which is the innermost covering layer 6, is lower than the acoustic impedance of the case body 3 and lower than the acoustic impedance of the covering layer 6 in contact with the outer surface 5a of the innermost covering layer 5.

[0014] Furthermore, "inside" refers to the inner side Xb in the direction perpendicular to the outer surface X, which is the side of the rotating electric machine 2 that is the source of vibration, as shown in Figure 2. "Outside," which will be described later, refers to the side opposite to the inner side Xb in the direction perpendicular to the outer surface X, that is, the side away from the rotating electric machine 2 that is the source of vibration, which is the outer side Xa in the direction perpendicular to the outer surface.

[0015] Acoustic impedance is a numerical representation of how easily sound propagates, and is expressed as the product of the density of the medium through which sound propagates and the speed of sound in that medium. The higher the acoustic impedance, the easier it is for sound (vibration) to propagate in that medium. When sound (vibration) propagates through different media, if the difference in acoustic impedance at the boundary between the media is large, the sound (vibration) is more likely to be reflected at the boundary, and if the difference in acoustic impedance is small, the sound (vibration) is more likely to pass through the boundary. In other words, if the difference in acoustic impedance at the boundary between the media is large, a larger proportion of the vibration is reflected back to the source of the vibration, and if the difference in acoustic impedance is small, a larger proportion of the vibration is transmitted and propagated away from the source of the vibration. In this embodiment, the side on which the vibration is transmitted and propagated is the outer Xa in the direction perpendicular to the outer surface, and the side on which the vibration is reflected back to the source of the vibration is the inner Xb in the direction perpendicular to the outer surface.

[0016] In this embodiment, such a medium boundary corresponds to the boundary between the outer surface 3a of the case body 3 and the covering member 4, and the boundaries between the multiple covering layers 6 in the covering member 4. Depending on the difference between the acoustic impedance of the innermost covering layer 5 and the acoustic impedance of the case body 3, a portion of the vibration from the rotating electric machine 2, which is the vibration source, is reflected back to the rotating electric machine 2. Furthermore, in the covering member 4, depending on the difference between the acoustic impedance of the innermost covering layer 5 and the acoustic impedance of the covering layer 6 in contact with the outer surface 5a of the innermost covering layer 5, a portion of the vibration from the rotating electric machine 2 that has propagated to the innermost covering layer 5 is further reflected back to the rotating electric machine 2.

[0017] For example, multiple coating layers 6 are formed by coating the outer surface 3a of the case body 3, or the outer surface 6a of an adjacent coating layer 6 on the inner side Xb perpendicular to the outer surface. Here, coating means covering the surface of an object to be coated with a fixable substance or object (e.g., application, painting, plating, vapor deposition, etc.). By forming the coating layers 6 by coating, the cost of providing the coating members 4 can be kept low. The coating members 4 only need to be provided so as to cover the outer surface of the case body 3, and may be attached to the case body 3 by adhesive. Adhesion is not limited to the form of applying adhesive to the target coating layer 6 and attaching it to the case body 3 or the inner coating layer 6. The target coating layer 6 may be a seal-like member with adhesive applied. As described above, since vibrations are reflected due to the difference in acoustic impedance at the boundary of each coating layer 6, the thickness of each layer of coating layer 6 is not required. The thickness of each coating layer 6 is, for example, several tens [μm] to several hundred [μm]. Therefore, even if the case body 3 is covered with a covering member 4 having multiple covering layers 6, it is easy to suppress an increase in the dimensions of the case 1.

[0018] As shown in FIGS. 2 to 6, in this embodiment, an example is illustrated in which the covering member 4 is configured to include even-numbered layers of covering layers 6. As will be described later, considering the difference in acoustic impedance at the boundary between the case body 3 with high acoustic impedance and the covering member 4, and the difference in acoustic impedance at the boundary between the air with low acoustic impedance and the covering member 4, it is preferable that the covering member 4 is configured to include even-numbered layers of covering layers 6 in which layers with low acoustic impedance and layers with high acoustic impedance are alternately arranged. However, it does not prevent the covering member 4 from being configured to include odd-numbered layers of covering layers 6. As described above, when vibration propagates through media with different vibrations, vibration is likely to be reflected if the difference in acoustic impedance at the boundary portion of the media is large. Therefore, it is preferable that the difference in acoustic impedance between adjacent covering layers 6 of the plurality of covering layers 6 is at least 10 times or more, preferably 100 times or more. In addition, when there are three or more covering layers 6, it is preferable that the acoustic impedance of each covering layer 6 is at least two different types of values. If the difference in acoustic impedance between adjacent covering layers 6 can be ensured to be 10 times or more, the acoustic impedance may be three or more different types of values.

[0019] As shown in FIG. 3, the covering member 4 is configured to include at least two layers of covering layers 6. The case body 3 is made of a metal such as aluminum or iron. Since the metal is a medium with relatively high acoustic impedance, the innermost covering layer 5 is formed of a soft resin such as rubber, which is a medium with relatively low acoustic impedance. For example, it is suitable that the innermost covering layer 5 is formed of butyl rubber, foamed urethane, polyamideimide, or the like. When the covering member 4 is configured to include two layers of covering layers 6, the covering layer 6 that contacts the outer surface 5a of the innermost covering layer 5 is the outermost covering layer 7 arranged on the outermost side (outer side Xa in the direction perpendicular to the outer surface). The outermost covering layer 7 is formed of a hard medium such as glass or carbon, which has a higher acoustic impedance than the innermost covering layer 5. For example, the outermost covering layer 7 is formed of a glass fiber sheet, a carbon fiber sheet, a metal sheet, metal plating, metal vapor deposition, or the like.

[0020] As shown in FIG. 4, when the covering member 4 is configured to include four covering layers 6, the first covering layer 61, the second covering layer 62, the third covering layer 63, and the fourth covering layer 64 are arranged from the inner side Xb in the direction orthogonal to the outer surface toward the outer side Xa in the direction orthogonal to the outer surface. In this form, the first covering layer 61 is the innermost covering layer 5, and the fourth covering layer 64 is the outermost covering layer 7. The acoustic impedance of the innermost covering layer 5 (the first covering layer 61) is lower than the acoustic impedance of the case body 3 and lower than the acoustic impedance of the covering layer 6 (the second covering layer 62) that contacts the outer surface 5a of the innermost covering layer 5. Also, the acoustic impedance of the second covering layer 62 is higher than the acoustic impedance of the covering layer 6 (the third covering layer 63) that contacts the outer surface 6a of the second covering layer 62. For example, the acoustic impedance of the first covering layer 61 (the innermost covering layer 5) and the acoustic impedance of the third covering layer 63 are the same value. Also, the acoustic impedance of the fourth covering layer 64 (the outermost covering layer 7) is higher than the acoustic impedance of the covering layer 6 (the third covering layer 63) that contacts the inner surface 7b of the outermost covering layer 7. For example, the acoustic impedance of the fourth covering layer 64 (the outermost covering layer 7) and the acoustic impedance of the second covering layer 62 are the same value.

[0021] Thus, it is preferable that the covering layer 6 is configured such that low impedance layers (for example, the first covering layer 61 and the third covering layer 63) with low acoustic impedance and high impedance layers (for example, the second covering layer 62 and the fourth covering layer 64) with high acoustic impedance are alternately arranged from the inner side Xb in the direction orthogonal to the outer surface toward the outer side Xa in the direction orthogonal to the outer surface.

[0022] The plurality of covering layers 6 are arranged such that the inner surface 6b (including the inner surface 7b of the outermost covering layer 7) and the outer surface 6a (including the outer surface 5a of the innermost covering layer 5) of adjacent covering layers 6 contact each other. Also, the inner surface 5b of the innermost covering layer 5 is arranged to contact the outer surface 3a of the case body 3. Also, the outer surface 7a of the outermost covering layer 7 is in contact with air. Air is a medium with low acoustic impedance, and when the covering member 4 includes an even number of covering layers 6, air with low acoustic impedance contacts the outermost covering layer 7 with relatively high acoustic impedance.

[0023] Thus, each of the coating layers 6 constituting the coating member 4 has a large difference in acoustic impedance with the adjacent medium in the direction X perpendicular to the outer surface. That is, the difference in acoustic impedance becomes large at each boundary in the direction in which vibration propagates (direction X perpendicular to the outer surface), so the proportion of vibration transmitted at each boundary can be reduced. As a result, vibrations from the vibration source propagating outside case 1 can be suppressed.

[0024] As mentioned above, air is a medium with low acoustic impedance. Therefore, at least a portion of the low-impedance layer of the coating layer 6 (here, the first coating layer 61 having a hollow portion 60) may be formed of air, as illustrated in Figure 5. Alternatively, as shown in Figure 6, the low acoustic impedance of air can be utilized by forming the low-impedance layer of the coating layer 6 (here, the first coating layer 61 and the third coating layer 63) with a foamed material containing air bubbles 9. In other words, the coating member 4 preferably includes a foamed layer containing air bubbles 9 or a hollow layer containing a hollow portion 60 as at least one coating layer 6 other than the outermost coating layer 7 that is in contact with air on the outer surface 7a. The hollow portion 60 can be formed by cutting out a portion of the coating layer 6 that forms the hollow layer and attaching the next coating layer 6 to the outer side Xa in the direction perpendicular to the outer surface of the hollow layer. Alternatively, the hollow layer may be composed of a sheet-like material with the portion that will become the hollow portion 60 pre-cut out.

[0025] The following is a brief summary of case (1) described above.

[0026] In one embodiment, a case (1) housing a vibration source (2) comprises a case body (3) that constitutes the outer shape, and a covering member (4) that covers at least a portion of the outer surface (3a) of the case body (3), wherein the covering member (4) comprises a plurality of covering layers (6), and the acoustic impedance of the innermost covering layer (5), which is the innermost covering layer (6) located at the Xb, is lower than the acoustic impedance of the case body (3) and lower than the acoustic impedance of the covering layer (6) in contact with the outer surface (5a) of the innermost covering layer (5).

[0027] With this configuration, at the boundaries between parts with different acoustic impedances—the boundary between the case body (3) and the innermost covering layer (5), and the boundary between the covering layer (6) in contact with the outer surface (5a) of the innermost covering layer (5) and the innermost covering layer (5)—vibrations transmitted from the vibration source (2) to the outside of the case (1) are reflected back to the vibration source (2), thereby reducing the vibrations transmitted to the outside of the case (1). Since the boundaries are utilized, the thickness of each covering layer (6) does not need to be specified, making it easier to keep the thickness of the covering member (4) down and preventing the case (1) from becoming larger. In other words, with this configuration, it is possible to reduce the noise generated in the case (1) that houses the vibration source (2) while suppressing an increase in size.

[0028] Furthermore, in case (1), it is preferable that the acoustic impedance of the outermost coating layer (7), which is the outermost coating layer (6) located at the Xa, is higher than the acoustic impedance of the coating layer (6) that is in contact with the inner surface (7b) of the outermost coating layer (7).

[0029] Air has a lower acoustic impedance than solids. With this configuration, by making the outermost coating layer (7) the coating layer (6) with the relatively higher acoustic impedance among the multiple coating layers (6), the difference in acoustic impedance between the outermost coating layer (7) and the air surrounding the case (1) can be increased. The larger the difference in acoustic impedance at the boundary, the larger the amplitude of the reflected vibrations, so vibrations transmitted outside the case (1) can be effectively reduced.

[0030] Furthermore, the case (1) preferably comprises, with the direction perpendicular to the outer surface (3a) of the case body (3) as the outer surface orthogonal direction (X), the covering member (4) having at least one of the covering layers (6) other than the outermost covering layer (7), which is the outermost covering layer (6), which is a foamed layer containing air bubbles (9) or a hollow layer containing a hollow portion (60).

[0031] Because air has a lower acoustic impedance than solids, this configuration allows the covering member (4) to effectively reduce vibrations transmitted from the vibration source (2) to the outer surface (3a) of the case body (3).

[0032] Furthermore, it is preferable that the case (1) is formed by coating a plurality of coating layers (6) on the outer surface (3a) of the case body (3), or on the outer surface (6a) of a coating layer (6) adjacent to the inner side (Xb) of the outer surface orthogonal direction (X), with the direction perpendicular to the outer surface (3a) of the case body (3).

[0033] By forming a coating layer (6), it is easy to keep the thickness of the coating layer (6) thin. Therefore, it is easy to prevent the case (1) from becoming larger due to the provision of the coating member (4). In addition, even if the shape of the outer surface (3a) of the case body (3) is not uniform, such as having irregularities, the coating member (4) can easily cover the outer surface (3a) of the case body (3) appropriately. [Explanation of Symbols]

[0034] 1: Case, 2: Rotating electric machine (vibration source), 3: Case body, 3a: Outer surface (of the case body), 4: Covering member, 5: Innermost covering layer, 5a: Outer surface (of the innermost covering layer), 5b: Inner surface (of the innermost covering layer), 6: Covering layer, 6a: Outer surface (of the covering layer), 6b: Inner surface (of the covering layer), 7: Outermost covering layer, 7a: Outer surface (of the outermost covering layer), 7b: Inner surface (of the outermost covering layer), 9: Air bubble, 60: Hollow part, X: Direction perpendicular to the outer surface, Xa: Outer side (outside) in the direction perpendicular to the outer surface, Xb: Inner side (inside) in the direction perpendicular to the outer surface

Claims

1. A case for housing a vibration source, The case body that makes up the exterior, The case body comprises a covering member that covers at least a portion of the outer surface, The covering member comprises a plurality of covering layers, A case in which the acoustic impedance of the innermost coating layer, which is the innermost coating layer, is lower than the acoustic impedance of the case body and lower than the acoustic impedance of the coating layer in contact with the outer surface of the innermost coating layer.

2. The case according to claim 1, wherein the acoustic impedance of the outermost coating layer, which is the outermost coating layer, is higher than the acoustic impedance of the coating layer in contact with the inner surface of the outermost coating layer.

3. The direction perpendicular to the outer surface of the case body is defined as the outer surface orthogonal direction. The case according to claim 1 or 2, wherein the covering member comprises at least one of the covering layers other than the outermost covering layer, which is the outermost covering layer, which is a foamed layer containing air bubbles or a hollow layer containing a hollow portion.

4. The direction perpendicular to the outer surface of the case body is defined as the outer surface orthogonal direction. The case according to claim 1 or 2, wherein the plurality of coating layers are formed by coating the outer surface of the case body or the outer surface of a coating layer adjacent to the inner side in a direction perpendicular to the outer surface.

Images