Patent Description:
As an example of rotating machines, Patent Document <NUM> discloses a centrifugal compressor including multiple stages of impellers arranged in the axial direction (for example, see Patent Document <NUM>).

Rotating machines such as a compressor are required to be smaller and less costly. As a method for responding to such requirements, for example, increasing the peripheral speed of the impeller may be mentioned.

However, simply increasing the rotational speed of the impeller increases the centrifugal force acting on the impeller, which causes an undesired phenomenon due to deformation of the impeller or the like. Therefore, it is not easy to increase the peripheral speed of the impeller.

In view of the above circumstances, an object of at least one embodiment of the present disclosure is to increase the peripheral speed of an impeller of a rotating machine.

According to at least one embodiment of the present disclosure, it is possible to increase the peripheral speed of an impeller of a rotating machine.

Embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions, and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present disclosure.

Hereinafter, a multi-stage centrifugal compressor including multiple stages of impellers arranged in the axial direction will be described as an example of the rotating machine.

<FIG> is a cross-sectional view of a centrifugal compressor according to some embodiments, taken along the axial direction of a rotational shaft.

As shown in <FIG>, the centrifugal compressor <NUM> includes a casing <NUM> and a rotor <NUM> rotatably supported within the casing <NUM>. The rotor <NUM> includes a rotational shaft <NUM> and multi-stage impellers <NUM> fixed to an outer surface of the shaft <NUM>.

The casing <NUM> accommodates a plurality of diaphragms <NUM> arranged in the axial direction. The diaphragms <NUM> are disposed so as to surround the impeller <NUM> from the radially outer side. Additionally, casing heads <NUM>, <NUM> are disposed on both sides of the diaphragms <NUM> in the axial direction.

The rotor <NUM> is rotatably supported by radial bearings <NUM>, <NUM> and a thrust bearing <NUM> so as to rotate around the center O.

A first end of the casing <NUM> has an intake port <NUM> through which a fluid enters from the outside, and a second end of the casing <NUM> has a discharge port <NUM> through which a fluid compressed by the centrifugal compressor <NUM> is discharged to the outside. Inside the casing <NUM>, a flow passage <NUM> is formed so as to connect the multi-stage impellers <NUM>. The intake port <NUM> communicates with the discharge port <NUM> via the impellers <NUM> and the flow passage <NUM>. The discharge port <NUM> is connected to a discharge pipe <NUM>.

A fluid which enters the centrifugal compressor <NUM> thorough the intake port <NUM> flows from upstream to downstream thorough the multi-stage impellers <NUM> and the flow passage <NUM>. The fluid is compressed stepwise by centrifugal force of the impellers <NUM> when passing through the multi-stage impellers <NUM>. The compressed fluid having passed through the most downstream impeller <NUM> of the multi-stage impellers <NUM> is guided to the outside through the scroll passage <NUM> and the discharge port <NUM>, and is discharged from an outlet portion <NUM> of a discharge passage <NUM> through the discharge pipe <NUM>.

In the following description, with respect to the axial direction of the centrifugal compressor <NUM>, the intake port <NUM> side is referred to as the upstream side, and the discharge port <NUM> side is referred to as the downstream side.

<FIG> is a schematic cross-sectional view of the impeller according to some embodiments, taken along the axial direction.

<FIG> is a schematic cross-sectional view of the impeller according to some embodiments, taken along the axial direction, for describing deformation of the impeller.

<FIG> is a schematic cross-sectional view of a conventional impeller, taken along the axial direction.

As shown in <FIG> and <FIG>, the impeller <NUM> according to the claimed invention includes a disc <NUM> disposed integrally with a hub <NUM> on the back side of the hub <NUM>, a cover <NUM> disposed on the opposite side of a radial passage <NUM> from the disc <NUM> in the axial direction, and a blade(s) <NUM> disposed between the disc <NUM> and the cover <NUM>. That is, the impeller <NUM> according to the claimed invention is a so-called closed impeller.

For convenience of explanation, with respect to the impeller <NUM>, the axially upstream side of the centrifugal compressor <NUM> is referred to as the cover side, and the axially downstream side is referred to as the disc side.

In the impeller <NUM> according to some embodiments, the hub <NUM> has a through hole <NUM> into which the shaft <NUM> is inserted. In some embodiments, in a region on the cover side of the through hole <NUM>, a fastening portion <NUM> to be fastened to the shaft <NUM> by shrink fitting is disposed. In other words, the impeller <NUM> according to some embodiments is fastened to the shaft <NUM> at the fastening portion <NUM> by shrink fitting.

In the impeller <NUM> according to some embodiments, a back surface <NUM> of the disc <NUM> has a recess <NUM> extending in the circumferential direction in a radial range where the blade <NUM> is disposed. In the impeller <NUM> according to some embodiments, the recess <NUM> is a portion recessed toward the cover side on the back surface <NUM> of the disc <NUM>, and is formed over the entire circumference of the disc <NUM>, for example.

Further, in the impeller <NUM> according to the claimed invention, the disc <NUM> has an inner protruding portion <NUM> disposed radially inward of the recess <NUM> on the back surface <NUM> of the disc <NUM>; and an outer protruding portion <NUM> disposed radially outward of the recess <NUM> on the back surface <NUM> of the disc <NUM>.

In <FIG>, the unevenness of the disc <NUM> in the axial direction are exaggerated.

Further, in <FIG>, the shape of a back surface 101X of a disc 100X of a conventional impeller 8X (see <FIG>) which does not have the recess <NUM>, the inner protruding portion <NUM>, and the outer protruding portion <NUM> is represented by the two-dot chain line.

As described above, since the unevenness of the disc <NUM> in the axial direction are exaggeratedly shown in <FIG>, the axial position of the back surface <NUM> of the disc <NUM> of the impeller <NUM> according to some embodiments is not necessarily entirely located on the disc side (downstream side) of the axial position of the back surface 101X of the disc 100X of the conventional impeller 8X. For example, in at least a partial region of the recess <NUM>, the axial position of the back surface <NUM> of the disc <NUM> of the impeller <NUM> according to some embodiments may be located on the cover side (upstream side) of the axial position of the back surface 101X of the disc 100X of the conventional impeller 8X. In other words, for example in at least a partial region of the recess <NUM>, the thickness of the disc <NUM> of the impeller <NUM> according to some embodiments may be smaller than the thickness of a region of the disc 100X of the conventional impeller 8X corresponding in radial position to the partial region. Further, for example in at least a partial region of the outer protruding portion <NUM>, the axial position of the back surface <NUM> of the disc <NUM> of the impeller <NUM> according to some embodiments may be located on the cover side (upstream side) of the axial position of the back surface 101X of the disc 100X of the conventional impeller 8X.

In the impeller <NUM> according to some embodiments, the cover <NUM> has a cover protruding portion <NUM> which protrudes so as to have a maximum thickness D between a radially inner end <NUM> and a radially outer end <NUM>.

In other words, the cover <NUM> according to some embodiments is shaped such that an outer surface <NUM> of the cover <NUM> is partially raised and the thickness is partially increased.

In <FIG>, the unevenness of the cover <NUM> in the thickness direction are exaggerated.

Further, in <FIG>, the shape of an outer surface 201X of a cover 200X of the conventional impeller 8X which does not have the cover protruding portion <NUM> is represented by the two-dot chain line.

The portion of the cover protruding portion <NUM> with the maximum thickness D is referred to as a top portion <NUM>.

As described above, since the unevenness of the cover <NUM> in the thickness direction are exaggeratedly shown in <FIG>, the thickness of the cover <NUM> of the impeller <NUM> according to some embodiments is not necessarily entirely greater than the thickness of the cover 200X of the conventional impeller 8X. In other words, the thickness of the cover <NUM> of the impeller <NUM> according to some embodiments may be at least partially smaller than the thickness of the cover 200X of the conventional impeller 8X.

When the rotational speed of the impeller is increased to respond to requirements of increasing the peripheral speed of the impeller, the centrifugal force acting on the impeller is increased, which causes an undesired phenomenon in the conventional impeller 8X due to deformation of the impeller 8X or the like.

Generally, as with the impeller <NUM> according to some embodiments, the conventional impeller 8X has a fastening portion <NUM> disposed at the axial position on the cover side of the through hole <NUM> into which the shaft <NUM> is inserted, and is thereby fastened to the shaft <NUM> by shrink fitting. Accordingly, as the centrifugal force acts on the peripheral portion of the through hole <NUM>, the fastening force tends to decrease, so that the fastening force may become insufficient due to increasing the peripheral speed. Further, when the impeller 8X is fastened to the shaft <NUM> at the fastening portion <NUM> disposed at the axial position on the cover side of the through hole <NUM>, as shown by the dotted line and the arrow <NUM> in <FIG>, the centrifugal force tends to deform the impeller 8X so that it rises radially outward on the disc side. Such deformation may cause problems such as contact between the impeller 8X and the diaphragm <NUM> around the impeller 8X.

As a result of studies by the inventors, it was found that when the recess <NUM> extending in the circumferential direction is provided on the back surface <NUM> of the disc <NUM> in the radial range where the blade <NUM> is located, it is possible to suppress the reduction in fastening force with the shaft <NUM> by the following principle. Specifically, as shown in <FIG>, when the centrifugal force acts on the disc <NUM>, the disc <NUM> is deformed so as to fall toward the cover side as described above, and the cover <NUM> is pressed through the blade <NUM>. At this time, when the disc <NUM> has the recess <NUM>, the recess <NUM> acts as a bending point, and a region 100b of the disc <NUM> on the radially outer side of the recess <NUM> is deformed so as to further fall from the disc side to the cover side as shown by the arrow <NUM> with respect to a region 100a on the radially inner side of the recess <NUM>. In other words, when the disc <NUM> has the recess <NUM>, a relatively radially outer region of the disc <NUM> is deformed so as to further fall from the disc side to the cover side, as compared with the case where the disc <NUM> does not have the recess <NUM>. Accordingly, a relatively radially outer region 200b of the cover <NUM> is pressed in the direction from the disc side to the cover side as shown by the arrow <NUM>, so that pressing force F having radially inward components acts on a relatively radially inner region 200a of the cover <NUM> as shown by the arrow <NUM>.

As a result, radially outward expansion in the vicinity of the fastening portion <NUM> is suppressed, so that the reduction in the fastening force is suppressed.

Therefore, with the impeller <NUM> according to the claimed invention, it is possible to suppress the reduction in fastening force and contribute to the increase in peripheral speed of the impeller <NUM>.

As a result of studies by the inventors, it was found that the deepest portion <NUM> of the recess <NUM> is desirably located in the range of <NUM>% or more and <NUM>% or less of the outer diameter of the disc <NUM> in order to effectively suppress the reduction in fastening force with the shaft <NUM> as described above.

Thus, in the impeller <NUM> according to some embodiments, the radial position of the recess <NUM> is set such that the deepest portion <NUM> of the recess <NUM> is in the range of <NUM>% or more and <NUM>% or less of the outer diameter of the disc <NUM>. Thus, it is possible to effectively suppress the reduction in fastening force with the shaft <NUM>.

In the impeller <NUM> according to the claimed invention, the disc <NUM> has an inner protruding portion <NUM> and an outer protruding portion <NUM> on the back surface <NUM> of the disc <NUM>.

As described above, the centrifugal force tends to deform the impeller <NUM> so that it rises radially outward on the disc side.

Therefore, for reducing the circumferential stress in order to suppress such deformation, it is conceivable to increase the thickness of the disc <NUM>, for instance. However, when the thickness of the disc <NUM> is simply increased, the weight of the impeller <NUM> increases, so that the centrifugal force also increases, and the circumferential stress may not be effectively reduced. Further, since the disc <NUM> is provided with a plurality of blades <NUM>, a high stress may be locally generated in the disc <NUM> due to a force received from the blades <NUM>. Accordingly, for example, when the thickness of the disc <NUM> is reduced in order to reduce the centrifugal force, the influence of the local stress generated in the disc <NUM> may increase.

In order to effectively reduce the circumferential stress in the disc <NUM>, it is desirable to increase the thickness of a relatively inner region in the radial direction.

Therefore, with the impeller <NUM> according to the claimed invention, since the inner protruding portion <NUM> is provided, it is possible to effectively reduce the circumferential stress in the disc <NUM> (hub <NUM>).

Further, as a result of studies by the inventors, it was found that when the outer protruding portion <NUM> is provided, is possible to reduce the influence of the local stress generated in the disc <NUM> as described above.

Therefore, with the impeller <NUM> according to the claimed invention, it is possible to reduce the influence of the local stress generated in the disc <NUM>.

In the impeller <NUM> according to some embodiments, the inner protruding portion <NUM> may be formed uniformly along the circumferential direction, i.e., such that the protrusion amount in the axial direction is constant regardless of the position in the circumferential direction. Alternatively, as described later, in the impeller <NUM> according to some embodiments, the protrusion amount of the inner protruding portion <NUM> may vary with the position in the circumferential direction.

Further, in the impeller <NUM> according to some embodiments, the outer protruding portion <NUM> may be formed uniformly along the circumferential direction. Alternatively, as described later, in the impeller <NUM> according to some embodiments, the protrusion amount of the outer protruding portion <NUM> may vary with the position in the circumferential direction.

In the impeller <NUM> according to some embodiments, as shown in <FIG>, when an axial distance B between the deepest portion <NUM> of the recess <NUM> and the top <NUM> of the inner protruding portion <NUM> is <NUM>, an axial distance A between the deepest portion <NUM> and the top <NUM> of the outer protruding portion <NUM> may be <NUM> to <NUM> (both inclusive).

As a result of studies by the inventors, it was found that if the axial distance A between the deepest portion <NUM> and the top <NUM> of the outer protruding portion <NUM> is less than <NUM> when the axial distance B between the deepest portion <NUM> of the recess <NUM> and the top <NUM> of the inner protruding portion <NUM> is <NUM>, the effect of the provision of the outer protruding portion <NUM> as described above may be insufficient. Further, it was found that if the axial distance A between the deepest portion <NUM> and the top <NUM> of the outer protruding portion <NUM> is more than <NUM> when the axial distance B between the deepest portion <NUM> of the recess <NUM> and the top <NUM> of the inner protruding portion <NUM> is <NUM>, disadvantages due to the increase in weight of the disc <NUM> in the radially outer region 110b of the recess <NUM> may increase.

Therefore, with the impeller <NUM> according to some embodiments, since the axial distance A is set from <NUM> to <NUM> when the axial distance B is <NUM>, it is possible to effectively reduce the influence of the local stress generated in the disc <NUM>.

In the impeller <NUM> according to the claimed invention, as shown in <FIG> and <FIG>, the inner protruding portion <NUM> is shaped such that the axial position of the inner protruding portion <NUM> approaches the cover <NUM> from the top <NUM> of the inner protruding portion <NUM> toward the radially inner side. In other words, in the impeller <NUM> according to the claimed invention, as shown in <FIG> and <FIG>, the inner protruding portion <NUM> is formed such that the thickness of the disc <NUM> gradually decreases from the top <NUM> of the inner protruding portion <NUM> toward the radially inner side.

As a result of studies by the inventors, it was found that even when the thickness of the disc <NUM> is increased in a region on the radially inner side of the top <NUM> shown in <FIG> and <FIG>, the effect of reducing the circumferential stress is relatively small although the weight of the disc <NUM> increases. Therefore, as shown in <FIG> and <FIG>, when the inner protruding portion <NUM> is shaped such that the axial position of the inner protruding portion <NUM> approaches the cover <NUM> from the top <NUM> of the inner protruding portion <NUM> toward the radially inner side, it is possible to suppress the increase in weight of the disc <NUM> while reducing the circumferential stress in the disc <NUM>.

In the impeller <NUM> according to some embodiments, the back surface <NUM> of the disc <NUM> may be uneven in the circumferential direction in a radial position where the inner protruding portion <NUM> is located.

Specifically, since the disc <NUM> is provided with the blades <NUM> arranged at intervals in the circumferential direction, the stress generated in the disc <NUM> varies with the position in the circumferential direction. As a result of diligent studies by the inventors paying attention to this point, it was found that when the protrusion amount of the inner protruding portion <NUM> is varied with the position in the circumferential direction, it is possible to suppress the increase in weight due to the provision of the inner protruding portion <NUM> while reducing the circumferential stress in the disc <NUM>.

Therefore, with the impeller <NUM> according to some embodiments, since the back surface <NUM> of the disc <NUM> is formed so as to be uneven in the circumferential direction in the radial range where the inner protruding portion <NUM> is located, it is possible to suppress the increase in weight due to the provision of the inner protruding portion <NUM> while reducing the circumferential stress in the disc <NUM>.

More specifically, the back surface <NUM> of the disc <NUM> is preferably formed as described below.

<FIG> is a schematic cross-sectional view taken along the line IV(A) in <FIG>, i.e., at the radial position where the inner protruding portion <NUM> is located.

In the impeller <NUM> according to some embodiments, for example as shown in <FIG>, the thickness of the disc <NUM> in the radial position of the inner protruding portion <NUM> may be greater at a circumferential position P1 of the disc <NUM> corresponding to the installation position of each blade <NUM> than at a circumferential position P2 of the disc <NUM> corresponding to the intermediate position between two blades <NUM> adjacent along the circumferential direction.

In other words, for example, the inner protruding portion <NUM> according to some embodiments may be formed so as to have alternately in the circumferential direction a first protruding portion <NUM> with a relatively great axial protrusion amount at the circumferential position P1 corresponding to the installation position of each blade <NUM>, and a second protruding portion <NUM> with a relatively small axial protrusion amount at the circumferential position P2 corresponding to the intermediate position between two blades <NUM> adjacent along the circumferential direction.

As a result of studies by the inventors, it was found that it is not necessary to increase the thickness of the disc <NUM> at the circumferential position P2 corresponding to the intermediate position between two adjacent blades.

Therefore, with the impeller <NUM> according to some embodiments, since the inner protruding portion <NUM> is formed so as to have alternately the first protruding portion <NUM> and the second protruding portion <NUM> in the circumferential direction, it is possible to effectively suppress the increase in weight due to the provision of the inner protruding portion <NUM> while reducing the circumferential stress in the disc <NUM>.

In the impeller <NUM> according to some embodiments, as shown in <FIG> and <FIG>, the outer protruding portion <NUM> may be shaped such that the axial position of the outer protruding portion <NUM> approaches the cover <NUM> from the top <NUM> of the outer protruding portion <NUM> toward the radially outer side. In other words, in the impeller <NUM> according to some embodiments, as shown in <FIG> and <FIG>, the outer protruding portion <NUM> may be formed such that the thickness of the disc <NUM> gradually decreases from the top <NUM> of the outer protruding portion <NUM> toward the radially outer side.

The magnitude of centrifugal force is proportional to the distance from the center O and the mass. Therefore, from the viewpoint of reducing the centrifugal force acting on the disc <NUM>, it is desirable that the thickness of the disc <NUM> decreases as the distance from the center O of the disc <NUM> increases. Therefore, as shown in <FIG> and <FIG>, when the outer protruding portion <NUM> is shaped such that the axial position of the outer protruding portion <NUM> approaches the cover <NUM> from the top <NUM> of the outer protruding portion <NUM> toward the radially outer side, it is possible to reduce the centrifugal force acting on the disc <NUM>.

In the impeller <NUM> according to some embodiments, the back surface <NUM> of the disc <NUM> may be uneven in the circumferential direction in a radial position where the outer protruding portion <NUM> is located.

As a result of studies by the inventors, it was found that, in the region 100b on the radially outer side of the recess <NUM>, the local stress generated in the disc <NUM> is affected by the blades <NUM> attached at intervals in the circumferential direction and thus fluctuates periodically along the circumferential direction.

Therefore, with the impeller <NUM> according to some embodiments, since the back surface <NUM> of the disc <NUM> is formed so as to be uneven in the circumferential direction in the radial range where the outer protruding portion <NUM> is located, it is possible to suppress the increase in weight due to the provision of the outer protruding portion <NUM> while reducing the local stress generated in the disc <NUM>.

<FIG> is a schematic cross-sectional view taken along the line IV(B) in <FIG>, i.e., at the radial position where the radially inner region 150a of the outer protruding portion <NUM> is located.

In the impeller <NUM> according to some embodiments, for example as shown in <FIG>, in a radial position where the radially inner region 150a of the outer protruding portion <NUM> is located, the thickness of the disc <NUM> may be greater at a position P3 of the disc <NUM> on the pressure side 85P of the blade <NUM> than at a position P4 of the disc <NUM> on the suction side <NUM> of the blade <NUM> with respect to the circumferential position P1 of the disc <NUM> corresponding to the installation position of the blade <NUM>.

In other words, for example, the outer protruding portion <NUM> according to some embodiments may be formed such that a third protruding portion <NUM> with a relatively great axial protrusion amount is formed at the position P3 on the pressure side 85P of the blade <NUM> with respect to the circumferential position P1 corresponding to the installation position of the blade <NUM>. Additionally, in the disc <NUM> according to some embodiments, a recessed portion <NUM> with a thickness of the disc <NUM> smaller than the thickness of the disc <NUM> including at least the third protruding portion <NUM> may be formed at the position P4 on the suction side <NUM> of the blade <NUM> with respect to the circumferential position P1 corresponding to the installation position of the blade <NUM>. The axial position of at least a partial region of the recessed portion <NUM> according to some embodiments may be located on the cover side (upstream side) of the axial position of the back surface 101X of the disc 100X of the conventional impeller 8X.

As a result of studies by the inventors, it was found that, in the relatively radially inner region 150a of the region 100b on the radially outer side of the recess <NUM>, the local stress generated in the disc <NUM> is relatively high at the position P3 on the pressure side 85P of the blade <NUM> with respect to the circumferential position P1 corresponding to the installation position of the blade <NUM>.

Therefore, with the impeller <NUM> according to some embodiments, since the outer protruding portion <NUM> is formed such that the third protruding portion <NUM> appears periodically along the circumferential direction, it is possible to suppress the increase in weight due to the provision of the outer protruding portion <NUM> while reducing the local stress generated in the disc <NUM>. Further, as described above, the outer protruding portion <NUM> may be formed such that the recessed portion <NUM> appears periodically along the circumferential direction, i.e., the third protruding portion <NUM> and the recessed portion <NUM> are alternated along the circumferential direction.

<FIG> is a schematic cross-sectional view taken along the line IV(C) in <FIG>, i.e., at the radial position where the radially outer region 150b of the outer protruding portion <NUM> is located.

In the impeller <NUM> according to some embodiments, for example as shown in <FIG>, in a radial position where the radially outer region 150b of the outer protruding portion <NUM> is located, the thickness of the disc <NUM> may be greater at a circumferential position P2 corresponding to the intermediate position between two blades <NUM> adjacent along the circumferential direction than at a circumferential position P1 corresponding to the installation position of each blade <NUM>.

In other words, for example, the outer protruding portion <NUM> according to some embodiments may be formed such that a fourth protruding portion <NUM> protruding in the axial direction is formed at the circumferential position P2 corresponding to the intermediate position between two blades <NUM> adjacent along the circumferential direction. Additionally, in the disc <NUM> according to some embodiments, a recessed portion <NUM> with a thickness of the disc <NUM> smaller than the thickness of the disc <NUM> including at least the fourth protruding portion <NUM> may be formed at the circumferential position P1 corresponding to the installation position of the blade <NUM>. The axial position of at least a partial region of the recessed portion <NUM> according to some embodiments may be located on the cover side (upstream side) of the axial position of the back surface 101X of the disc 100X of the conventional impeller 8X.

As a result of studies by the inventors, it was found that, in the relatively radially outer region 150b of the region 100b on the radially outer side of the recess <NUM>, the local stress generated in the disc <NUM> is relatively high at the circumferential position P2 corresponding to the intermediate position between two blades <NUM> adjacent along the circumferential direction.

Therefore, with the impeller <NUM> according to some embodiments, since the outer protruding portion <NUM> is formed such that the fourth protruding portion <NUM> appears periodically along the circumferential direction, it is possible to suppress the increase in weight due to the provision of the outer protruding portion <NUM> while reducing the local stress generated in the disc <NUM>. Further, as described above, the outer protruding portion <NUM> may be formed such that the recessed portion <NUM> appears periodically along the circumferential direction, i.e., the fourth protruding portion <NUM> and the recessed portion <NUM> are alternated along the circumferential direction.

Although not depicted, the axial position in at least a partial region on the radially outer side of the IV(C) section in <FIG> may be located on the cover side (upstream side) of the axial position of the back surface 101X of the disc 100X of the conventional impeller 8X over the entire circumference.

In the impeller <NUM> according to some embodiments, the cover <NUM> may have a minimum thickness C on the radially outer side of a radial position where the cover <NUM> has the maximum thickness D such that a ratio of the minimum thickness C to the maximum thickness D is in a range of <NUM> to <NUM> (both inclusive). In the case where the radially outer end <NUM> of the cover <NUM> protrudes radially outward from a trailing edge 85T of the blade <NUM>, the minimum thickness C is the minimum thickness of the portion of the cover <NUM> that protrudes radially outward from the trailing edge 85T of the blade <NUM>.

As described above, when the centrifugal force acts on the disc <NUM>, the disc <NUM> is deformed so as to fall toward the cover side, and the cover <NUM> is pressed through the blade <NUM>.

In the impeller <NUM> according to the claimed invention, since the disc <NUM> has the recess <NUM>, as described above, a relatively radially outer region of the disc <NUM> is deformed so as to further fall from the disc side to the cover side, as compared with the case where the disc <NUM> does not have the recess <NUM>.

When the disc <NUM> is deformed so as to further fall to the cover side, the relatively radially outer region 200b of the cover <NUM> is pressed mainly. Therefore, in order to generate pressing force F having radially inward components in the relatively radially inner region 200a of the cover <NUM>, it is desirable to improve the bending rigidity of the cover <NUM>, i.e., to increase the thickness of the cover <NUM>.

However, simply increasing the thickness of the cover <NUM> increases the centrifugal force acting on the cover <NUM>, so that the pressing force F is canceled under the influence of the increased centrifugal force.

Here, when the cover <NUM> is configured so as to have the maximum thickness D between the radially inner end <NUM> and the radially outer end <NUM>, it is possible to suppress the increase in centrifugal force that cancels the pressing force F even if the thickness of the cover <NUM> is increased.

Further, as a result of studies by the inventors, it was found that when the cover <NUM> is configured so as to have the minimum thickness C on the radially outer side of a radial position where the cover has the maximum thickness D such that a ratio of the minimum thickness C to the maximum thickness D is in the range of <NUM> to <NUM>, it is possible to reduce the thickness of the relatively radially outer region 200b of the cover <NUM>, so that it is possible to suppress the increase in weight of the impeller <NUM>.

Thus, with the impeller <NUM> according to some embodiments, it is possible to suppress the reduction in fastening force while suppressing the increase in weight of the impeller <NUM>.

In the impeller <NUM> according to some embodiments, the front surface (outer surface <NUM>) of the cover <NUM> may be uneven in the circumferential direction in a radial position where the cover <NUM> has the maximum thickness D.

As a result of studies by the inventors, it was found that, since the cover <NUM> is provided with the blades <NUM> at intervals in the circumferential direction, when the magnitude of the maximum thickness D, i.e., the thickness of the cover <NUM> is varied with the position in the circumferential direction in the radial position where the cover <NUM> has the maximum thickness D, it is possible to effectively generate the pressing force F, and it is possible to suppress the increase in weight due to increasing the thickness of the cover <NUM>.

Therefore, with the impeller <NUM> according to some embodiments, it is possible to suppress the increase in weight due to increasing the thickness of the cover <NUM> while effectively suppressing the reduction in fastening force.

More specifically, the outer surface <NUM> of the cover <NUM> is preferably formed as described below.

<FIG> is a schematic cross-sectional view taken along the line V(A) in <FIG>, i.e., at a position where the top portion <NUM> of the cover protruding portion <NUM> is located.

<FIG> is a schematic cross-sectional view taken along the line V(B) in <FIG>, i.e., at a position on the radially outer side of the top portion <NUM> of the cover protruding portion <NUM>.

<FIG> is a schematic cross-sectional view taken along the line V(C) in <FIG>, i.e., at a position on the radially outer side of the V(B) section in <FIG> of the cover protruding portion <NUM>.

In the impeller <NUM> according to some embodiments, for example as shown in <FIG>, in the radial position where the cover <NUM> has the maximum thickness D, the thickness of the cover <NUM> may be set as follows. Specifically, P6 is defined as a position of the cover <NUM> on the pressure side 85P of the blade <NUM> with respect to a circumferential position P5 of the cover <NUM> corresponding to the installation position of the blade <NUM>, and P7 is defined as a position of the cover <NUM> on the suction side <NUM> of the blade <NUM> with respect to the circumferential position P5. The thickness of the cover <NUM> may be greater at the position P6 than at the position P7.

In other words, for example as shown in <FIG>, the cover protruding portion <NUM> according to some embodiments may be formed such that, in the radial position where the top portion <NUM> of the cover protruding portion <NUM> is located, a first protruding portion <NUM> with a relatively great protrusion amount at the circumferential position P6 and a second protruding portion <NUM> with a relatively small protrusion amount at the circumferential position P7 are alternated in the circumferential direction.

Further, for example as shown in <FIG>, the cover protruding portion <NUM> according to some embodiments may be formed such that, on the radially outer side of the radial position where the top portion <NUM> of the cover protruding portion <NUM> is located, a third protruding portion <NUM> disposed in a circumferential position including the position P6 and a recessed portion <NUM> disposed in a circumferential position including the position P7 are alternated in the circumferential direction. The third protruding portion <NUM> is a portion with a protrusion amount which is relatively great but is smaller than the first protruding portion <NUM>. The recessed portion <NUM> is a portion where the thickness of the cover <NUM> is smaller than the thickness of the cover <NUM> including at least the third protruding portion <NUM>.

The thickness of the cover <NUM> in at least a partial region of the recessed portion <NUM> may be smaller than the thickness of a region of the cover 200X of the conventional impeller 8X corresponding in radial position to the partial region.

Further, for example as shown in <FIG>, the cover <NUM> according to some embodiments may be formed such that, on the radially outer side of the radial position where the third protruding portion <NUM> and the recessed portion <NUM> are formed, an outer peripheral region <NUM> including the position P6 and extending in the circumferential direction and a recessed portion <NUM> disposed in a circumferential position including the position P7 are alternated in the circumferential direction. The outer peripheral region <NUM> is a region where the thickness of the cover <NUM> is smaller than the thickness of the cover <NUM> including at least the third protruding portion <NUM>. The recessed portion <NUM> is a portion where the thickness of the cover <NUM> is smaller than that of the outer peripheral region <NUM>.

The thickness of the cover <NUM> in at least a partial region of the outer peripheral region <NUM> may be smaller than the thickness of a region of the cover 200X of the conventional impeller 8X corresponding in radial position to the partial region. Further, the thickness of the cover <NUM> in the recessed portion <NUM> may be smaller than the thickness of a region of the cover 200X of the conventional impeller 8X corresponding in radial position to this region.

As a result of studies by the inventors, it was found that when the thickness of the cover <NUM> is made greater at the position P6 on the pressure side 85P of the blade <NUM> than at the position P7 on the suction side <NUM> of the blade <NUM> with respect to the circumferential position P5 corresponding to the installation position of the blade <NUM>, it is possible to effectively generate the pressing force F.

In the impeller <NUM> according to some embodiments, as shown in <FIG>, an angle θ between the blade <NUM> and the cover <NUM> may be acute on the pressure side 85P of the blade <NUM>.

As a result of studies by the inventors, it was found that when the angle θ between the blade <NUM> and the cover <NUM> is acute on the pressure side 85P of the blade <NUM>, and the thickness of the cover <NUM> is made greater at the position P6 on the pressure side 85P of the blade <NUM> than at the position P7 on the suction side <NUM> of the blade <NUM> with respect to the circumferential position P5 corresponding to the installation position of the blade <NUM>, it is possible to more effectively generate the pressing force F.

Therefore, with the impeller <NUM> according to some embodiments, it is possible to suppress the increase in weight due to increasing the thickness of the cover <NUM> while more effectively suppressing the reduction in fastening force.

With the centrifugal compressor <NUM> according to some embodiments, since the impeller <NUM> according to the above-described embodiments is included, it is possible to increase the peripheral speed of the impeller <NUM>, so that it is possible to reduce the size and cost of the centrifugal compressor <NUM>.

The present disclosure is not limited to the embodiments described above, but includes modifications to the embodiments described above, and embodiments composed of combinations of those embodiments, as long as they fall within the scope defined by the appended claims.

For example, in the above-described embodiments, the impeller <NUM> has the recess <NUM>, the inner protruding portion <NUM>, the outer protruding portion <NUM>, and the cover protruding portion <NUM>. However, according to an embodiment not covered by the claimed invention, the impeller <NUM> may have the cover protruding portion <NUM> but may not have the recess <NUM>, the inner protruding portion <NUM>, and the outer protruding portion <NUM>. Further, according to an embodiment of the claimed invention, the impeller <NUM> has the recess <NUM>, the inner protruding portion <NUM>, and the outer protruding portion <NUM> but may not have the cover protruding portion <NUM>.

Claim 1:
An impeller (<NUM>) of a rotating machine, comprising:
a disc (<NUM>);
a cover (<NUM>) disposed on an opposite side of a radial passage (<NUM>) from the disc (<NUM>) in an axial direction; and
a blade (<NUM>) disposed between the disc (<NUM>) and the cover (<NUM>),
wherein a back surface (<NUM>) of the disc (<NUM>) has a recess (<NUM>) extending in a circumferential direction in a radial range where the blade (<NUM>) is disposed,
wherein the disc (<NUM>) has:
an inner protruding portion (<NUM>) disposed radially inward of the recess (<NUM>) on the back surface (<NUM>) of the disc (<NUM>);
an outer protruding portion (<NUM>) disposed radially outward of the recess (<NUM>) on the back surface (<NUM>) of the disc (<NUM>); and
characterized in that
the inner protruding portion (<NUM>) is formed such that a thickness of the disc (<NUM>) gradually decreases from a top (<NUM>) of the inner protruding portion (<NUM>) toward a radially inner side.