ROTARY MACHINE

A rotary machine includes an impeller which is attached to one end portion in an axial direction of a rotating shaft; and a bearing which is attached to the rotating shaft on a rear surface side of the impeller. The impeller includes a cylindrical boss portion, a hub portion, and a blade portion. A rear surface of the hub portion is provided with a recessed portion recessed toward the one end side from an end edge on the rear surface side of the hub portion in the axial direction. The other end in the axial direction of the boss portion is disposed inside the recessed portion, and an end surface on the one end side of the bearing is disposed inside the recessed portion.

TECHNICAL FIELD

This disclosure relates to a rotary machine in which a rotating shaft is supported by a bearing and an impeller attached to the rotating shaft can be rotated.

BACKGROUND ART

As such a technology, as described in Patent Document 1, an electric supercharger in which a compressor wheel (impeller) is attached to a rotating shaft and a motor rotor fixed to the rotating shaft is rotated by a motor is known. In the electric supercharger, a bearing is provided between the compressor wheel and the motor rotor. The bearing supports one side of the motor rotor.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the above-described structure in the related art, the bearing is provided between the rear surface side of the impeller and the motor rotor. Therefore, the length from the bearing to the tip end of the rotating shaft includes the entire axial length of the impeller. When the length from the bearing to the tip end of the rotating shaft is long, it is also difficult to increase the critical speed of the shaft system. This disclosure describes a rotating shaft capable of increasing the critical speed of a shaft system.

Solution to Problem

According to an aspect of this disclosure, a rotary machine includes: a rotating shaft rotatably supported in a housing; an impeller which is attached to one end portion in an axial direction of the rotating shaft and is rotatable integrally with the rotating shaft; and a bearing which is attached to the rotating shaft on a rear surface side of the impeller and rotatably supports the rotating shaft to the housing, in which the impeller includes a cylindrical boss portion through which the rotating shaft penetrates, a hub portion which is connected to the boss portion and extends in a radial direction of the rotating shaft, and a blade portion which protrudes from the boss portion and the hub portion in the radial direction and toward one end side in the axial direction, a rear surface of the huh portion is provided with a recessed portion recessed toward the one end side from an end edge on the rear surface side of the hub portion in the axial direction, the other end in the axial direction of the boss portion is disposed inside the recessed portion, and an end surface on the one end side of the bearing is disposed inside the recessed portion.

Effects of Invention

According to the aspect of this disclosure, the critical speed of a shaft system can be increased.

DESCRIPTION OF EMBODIMENTS

According to an aspect of this disclosure, a rotary machine includes: a rotating shaft rotatably supported in a housing; an impeller which is attached to one end portion in an axial direction of the rotating shaft and is rotatable integrally with the rotating shaft; and a bearing which is attached to the rotating shaft on a rear surface side of the impeller and rotatably supports the rotating shaft to the housing, in which the impeller includes a cylindrical boss portion through which the rotating shaft penetrates, a hub portion which is connected to the boss portion and extends in a radial direction of the rotating shaft, and a blade portion which protrudes from the boss portion and the hub portion in the radial direction and toward one end side in the axial direction, a rear surface of the hub portion is provided with a recessed portion recessed toward the one end side from an end edge on the rear surface side of the hub portion in the axial direction, the other end in the axial direction of the boss portion is disposed inside the recessed portion, and an end surface on the one end side of the bearing is disposed inside the recessed portion.

In the rotary machine, the impeller is provided with the recessed portion at the rear surface of the hub portion. Since the end surface of the bearing is disposed inside the recessed portion, the length from the bearing to the tip end of the rotating shaft can be reduced. Accordingly, the critical speed of the shaft system can be increased.

In some aspects, the housing is provided with a bearing surrounding portion which surrounds the bearing from an outer circumferential side and the one end side and protrudes into the recessed portion, and a facing surface of the bearing surrounding portion which faces the hub portion is curved along a surface of the recessed portion. In this case, not only the bearing but also the bearing surrounding portion, which is a part of the housing, also protrude into the recessed portion of the impeller and are disposed inside the recessed portion. Therefore, it becomes easier for the impeller to be brought close to the bearing. As a result, the amount of overhang of the shaft tip end portion and the center of gravity of the impeller from the bearing is reduced, and the above-described actions and effects are more favorably exhibited.

In some aspects, the housing is provided with a bearing surrounding portion which surrounds the bearing from an outer circumferential side and the one end side and protrudes into the recessed portion, and a part of the bearing surrounding portion faces the one end side of the bearing.

In some aspect, the bearing is a radial ball bearing including an inner race press-fitted to the rotating shaft and an outer race that is rotatable relative to the inner race via a plurality of balls, and the inner race abuts the boss portion of the impeller. In this case, the impeller is brought as close as possible to the bearing. Therefore, it becomes easier for the tip end of the rotating shaft to be brought close to the bearing, and the above-described actions and effects are more favorably exhibited.

In some aspect, the rotating shaft is provided with a rotor portion, the housing is provided with a stator portion, and the rotary machine is an electric supercharger which rotates the rotating shaft and the impeller by an interaction between the rotor portion and the stator portion.

Hereinafter, an embodiment of this disclosure will be described with reference to the drawings. In the description of the drawings, like elements are denoted by like reference numerals, and redundant descriptions will be omitted.

An electric supercharger (rotary machine)1according to a first embodiment will be described with reference toFIG. 1. As illustrated inFIG. 1, the electric supercharger1is applied to, for example, an internal combustion engine of a vehicle or a ship. The electric supercharger1includes a compressor7. In the electric supercharger1, a compressor impeller8is rotated by the interaction between a rotor portion13and a stator portion14to compress a fluid such as air and generate compressed air.

The electric supercharger1includes a rotating shaft12rotatably supported in a housing2and the compressor impeller8fixed to a tip end portion (one end portion)12aof the rotating shaft12. The housing2includes a motor housing3in which the rotor portion13and the stator portion14are stored, and an end wall4that closes an opening on the other end side (the right side in the figure) of the motor housing3. A compressor housing6in which the compressor impeller8is stored is provided on one end side (the left side in the figure) of the motor housing3. The compressor housing6includes an intake port9, a scroll portion10, and a discharge port11.

The compressor impeller8is made of, for example, a resin or carbon fiber reinforced resin (hereinafter, referred to as “CFRP”, CFRP: Carbon Fiber Reinforced Plastic), and thus a reduction in weight is achieved.

The rotor portion13is fixed to the center portion in an axial direction D1of the rotating shaft12and includes one or a plurality of permanent magnets (not illustrated) attached to the rotating shaft12. The stator portion14is fixed to the inner surface of the motor housing3so as to surround the rotor portion13, and includes a coil portion (not illustrated) having a lead wire14awound thereon. When an alternating current is supplied to the coil portion of the stator portion14through the lead wire14a, the rotating shaft12and the compressor impeller8rotate integrally due to the interaction between the rotor portion13and the stator portion14. When the compressor impeller8rotates, the compressor impeller8draws outside air through the intake port9, compresses the air through the scroll portion10, and discharges the air from the discharge port11. The compressed air discharged from the discharge port11is supplied to the internal combustion engine mentioned above.

The electric supercharger1includes two ball bearings (bearings)20that are press-fitted to the rotating shaft12and rotatably support the rotating shaft12to the housing2. The ball bearings20are respectively provided near the tip end portion12aand a base end portion12bof the rotating shaft12, and support the rotating shaft12at both sides. The ball bearing20is, for example, a grease lubrication type radial ball bearing. More specifically, the ball bearing20may be a deep groove ball bearing or an angular contact ball bearing. As illustrated inFIG. 2, the ball bearing20includes an inner race20apress-fitted to the rotating shaft12and an outer race20bthat is rotatable relative to the inner race20avia a plurality of balls20c.

One ball bearing20is attached to the rear surface side (the right side in the figure) of the compressor impeller8. A cylindrical bearing sleeve (cylindrical portion)21is attached to the outer circumferential side of one ball bearing20. As illustrated inFIG. 1, the ball bearing20and the bearing sleeve21are fixed to the rotating shaft12by a shaft end nut16provided at the tip end portion12aof the rotating shaft12. The cylindrical bearing sleeve21is disposed on the outer circumferential side of one ball bearing20. The bearing sleeve21is press-fitted into a bearing surrounding portion23formed on one end side in the axial direction D1of the motor housing3.

The other ball bearing20is attached between the rotating shaft12and the end wall4. A cylindrical bearing sleeve (cylindrical portion)22is attached to the outer circumferential side of the other ball bearing20. The bearing sleeve22is press-fitted to a cylindrical portion formed to protrude inward from the center of the end wall4in the motor housing3. An annular spring receiver26is provided between the other ball bearing20and the end wall4. The spring receiver26is biased toward one side in the axial direction D1by a spring27disposed in the cylindrical portion at the center of the end wall4.

The motor housing3is made of, for example, aluminum. On the other hand, the inner race20aand the outer race20bof the ball bearing20are made of iron. Therefore, the bearing sleeves21and22which are made of iron such as carbon steel and have the same degree of hardness as the ball bearings20are provided between the ball bearings20and the motor housing3. The bearing sleeves21and22surround the ball bearings20from the outer circumferential side. Accordingly, the motor housing3made of a relatively soft material is protected from attrition.

The rotating shaft12, and the compressor impeller8, the rotor portion13, the ball bearings20, and the spring receiver26fixed to the rotating shaft12integrally constitute a rotating section in the housing2and are biased toward one side in the axial direction D1. An annular portion23bwhich is a part of the hearing surrounding portion23faces one end side of the ball bearing20such that the rotating section is positioned in the axial direction D1.

Subsequently, the bearing structure of the electric supercharger1will be described in detail with reference toFIGS. 2 and 3. As illustrated inFIGS. 2 and 3, the compressor impeller8includes a cylindrical boss portion51through which the rotating shaft12penetrates, a hub portion52which is connected to the boss portion51and extends in a radial direction D2of the rotating shaft12, and a blade portion53which protrudes from the boss portion51and the hub portion52in the radial direction D2and toward one end side (the left side in the figure) in the axial direction D1.

The boss portion51abuts the inner race20aof the ball bearing20. The hub portion52has a curved surface. The blade portion53has a three-dimensional shape according to the performance required of the compressor impeller8.

The rear surface of the hub portion52is provided with a recessed portion8arecessed toward one end side (the left side in the figure) in the axial direction D1. The recessed portion8ais recessed toward one end side in the axial direction D1from an end edge52bon the rear surface side of the hub portion52in the axial direction D1. By forming the rear surface of the compressor impeller8into a cut-out shape as well as by causing the compressor impeller8to be made of CFRP, a reduction in the weight of the compressor impeller8is achieved.

Furthermore, the other end51ain the axial direction D1of the boss portion51is disposed in the recessed portion8a. One end surface20din the axial direction D1of the ball bearing20is disposed in the recessed portion8a. As illustrated inFIG. 3, an advancing length L by which one end surface20dof the ball bearing20advances into the recessed portion8amay be equal to or less than half of the length (thickness) in the axial direction D1of the ball bearing20, or may be equal to or less than ¼ thereof. The advancing length L may be equal to or more than half of the length (thickness) in the axial direction D1of the ball bearing20. In a case where a thin ball bearing20is employed, the entire ball bearing20may be disposed in the recessed portion8a.

One end surface20dof the inner race20aof the ball bearing20abuts the other end51aof the boss portion51in the recessed portion8a.

As illustrated inFIG. 2, the motor housing3is provided with the above-mentioned bearing surrounding portion23surrounding the ball bearing20from the outer circumferential side and one end side. The bearing surrounding portion23having a truncated cone shape protrudes into the recessed portion8a. In other words, the entirety or a part of the annular portion23bof the bearing surrounding portion23is disposed inside the recessed portion8a. A facing surface23aof the bearing surrounding portion23which faces the hub portion52is curved along the surface52aof the recessed portion8a. Accordingly, a gap that extends to be thinly curved is provided between the surface52aof the recessed portion8aand the facing surface23aof the bearing surrounding portion23.

In the electric supercharger1of this embodiment described above, the compressor impeller8is provided with the recessed portion8aat the rear surface of the huh portion52. Since one end surface20dof the ball bearing20is disposed inside the recessed portion8a, the length from the ball bearing20to the tip end12d(seeFIG. 3) of the rotating shaft12is reduced. Accordingly, the deflection amount of the tip end12dof the rotating shaft12of the electric supercharger1is reduced, and the critical speed of the shaft system increases. As the critical speed increases, the rotational speed of the rotating shaft12can be increased. In addition, since the length from the ball bearing20to the tip end12dof the rotating shaft12is reduced, the compressor impeller8can be reduced in weight, which in turn contributes to an improvement in transient performance.

In the electric supercharger1, not only the ball bearing20but also the bearing surrounding portion23, which is a part of the housing2, also protrude into the recessed portion8aof the compressor impeller8and are disposed inside the recessed portion8a. At least a part of the annular portion23bis disposed inside the recessed portion8a. Therefore, it becomes easier for the tip end12dof the rotating shaft12to be brought close to the ball bearing20, and the above-described actions and effects are more favorably exhibited.

Furthermore, the boss portion51of the compressor impeller8is brought as close as possible to the ball bearing20by being allowed to abut the ball bearing20. Therefore, it becomes easier for the tip end12dof the rotating shaft12to be brought close to the ball bearing20, and the above-described actions and effects are more favorably exhibited.

While the embodiment of this disclosure has been described above, the present invention is not limited to the embodiment. For example, instead of the electric supercharger1, the present invention can be applied to a known supercharger that rotates a rotating shaft and an impeller by the driving force of a turbine. Furthermore, for example, as illustrated inFIG. 4, two compressor impellers may be provided coaxially. In the example illustrated inFIG. 4, the compressor impeller8is fixed to one end portion12aof a rotating shaft12A, and a second compressor impeller60is fixed to the other end portion12bof the rotating shaft12A. The second compressor impeller60includes a boss portion61, a hub portion62, and a blade portion63, and a recessed portion60ais provided on the rear surface side of the hub portion62. The end surface20dof the ball bearing20is disposed inside the recessed portion60aand advances from an end edge62bby an advancing length L. Even with such a structure, the critical speed of the shaft system can be increased.

Furthermore, the bearing surrounding portion23may not protrude into the recessed portion8a. The facing surface23aof the bearing surrounding portion23may not be curved along the surface52aof the recessed portion8abut may be significantly distant from the surface52aof the recessed portion8a, or may have a different shape from the surface52aof the recessed portion8a.

Another member may be interposed between the ball bearing20and the boss portions51and61of the compressor impeller8and the second compressor impeller60.

The bearing is not limited to the grease lubrication type ball bearing. For example, a ball bearing employing another lubrication type (oil lubrication or the like) may also be used. The bearing is not limited to the ball bearing and may also be a sliding bearing.

The material of the impeller is not limited to CFRP. An impeller made of aluminum or an aluminum-containing material, or an impeller made of magnesium or a magnesium-containing material may also be employed. The shape and size (degree of cutting) of the recessed portion of the impeller can be appropriately changed.

The structure of the present invention can be applied to any rotary machine in which a bearing is press-fitted to a rotating shaft. For example, the present invention can be applied to a type of electric supercharger in which rotation is assisted by a motor provided with a turbine. Furthermore, the present invention is not limited to a rotary machine provided with a compressor, and can also be applied to a generator that generates electric power using a turbine.

INDUSTRIAL APPLICABILITY

According to some aspects of this disclosure, the critical speed of a shaft system can be increased.

REFERENCE SIGNS LIST