JP2014230393A - Rotary electric machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict a change in the ability of a rotor to cool by means of a liquid refrigerant, according to the rotating speed of the rotor.SOLUTION: When the rotor rotating speed is low, the number of communication passages that is open when cooling oil flows into a cooling passage 34 from a refrigerant introduction portion 38 into a cooling passage 34 increases. Accordingly, it is possible to restrict a decrease in an amount of cooling oil delivered to the cooling passage 34 from the refrigerant introduction port 38. On the other hand, when the rotor rotating speed is high, the number of communication passages that is open when the cooling oil flows into the cooling passage 34 from the refrigerant introduction port 38 decreases. Accordingly, it is possible to restrict an excessive increase in the amount of cooling oil delivered to the cooling passage 34 from the refrigerant introduction portion 38.

Description

  The present invention relates to a rotating electrical machine, and more particularly to a rotor cooling structure.

  In the rotating electrical machine disclosed in Patent Document 1 below, the permanent magnet of the rotor is cooled by supplying the cooling oil to the cooling flow path of the rotor using the centrifugal force accompanying the rotation of the rotor. In addition, by narrowing the inlet of the cooling flow path as the rotor speed increases, the cooling oil that acts as a resistance between the rotor and stator gaps at the time of high rotation of the rotor is reduced to improve the operating efficiency of the rotating electrical machine. I am trying.

JP 2009-290979 A JP 2009-118686 A

  In Patent Document 1, only the inlet of the cooling flow path is restricted, and the flow path area through which the cooling oil flows is constant regardless of the rotational speed of the rotor. Occurs. As a result, the cooling capacity of the rotor by the cooling oil varies according to the rotational speed of the rotor.

  In the present invention, when cooling oil is supplied to a cooling flow path of a rotor by using centrifugal force accompanying rotation of the rotor to cool the rotor, the cooling capacity of the rotor by liquid refrigerant depends on the rotational speed of the rotor. The purpose is to suppress fluctuations.

  The rotating electrical machine according to the present invention employs the following means in order to achieve the above-described object.

  A rotating electrical machine according to the present invention includes a rotor shaft in which a space in which liquid refrigerant is supplied is formed, and a rotor that is attached to the outer periphery of the rotor shaft and in which a cooling channel through which liquid refrigerant passes is formed. The rotor shaft and the rotor are formed with a plurality of communication channels for communicating the rotor shaft inner space and the rotor internal cooling channel, and the communication channel through which the liquid refrigerant passes as the rotational speed of the rotor shaft and the rotor increases. The gist is that the liquid refrigerant supplied to the rotor shaft internal space flows into the rotor internal cooling flow path through the communication flow path due to the rotation of the rotor shaft and the rotor.

  In one aspect of the present invention, a refrigerant supply member that supplies liquid refrigerant to the rotor shaft internal space is disposed in the rotor shaft internal space, communicates with the plurality of communication channels, and communicates the liquid refrigerant supplied from the refrigerant supply member. The refrigerant introduction port is formed in the inner circumference of the rotor shaft for introduction into the passage, and the refrigerant introduction port is configured so that the distance between the communication portion of the plurality of communication flow paths and the refrigerant introduction port with respect to the rotor rotation central axis varies in a plurality of ways. It is preferable that the inner diameter of the inner periphery of the rotor shaft is changed at the position where is formed.

  In one aspect of the present invention, it is preferable that the refrigerant supply port of the refrigerant supply member is disposed at a position facing the portion in the refrigerant introduction port where the inner diameter of the inner periphery of the rotor shaft is maximum in the radial direction.

  According to the present invention, when the liquid refrigerant supplied to the rotor shaft internal space flows into the rotor internal cooling flow path through the communication flow path by the rotation of the rotor shaft and the rotor, the rotational speed of the rotor shaft and the rotor is reduced. As the number of channels increases, the number of communication channels through which the liquid refrigerant passes decreases, so that the ability of the liquid refrigerant to be sent to the rotor internal cooling channel by centrifugal force can be prevented from fluctuating according to the rotational speed of the rotor. . As a result, the cooling capacity of the rotor by the liquid refrigerant can be suppressed from changing according to the rotational speed of the rotor.

It is sectional drawing which shows schematic structure of the stator and rotor seen from the direction orthogonal to a rotor rotation center axis. It is sectional drawing which shows schematic structure of the rotor and rotor shaft seen from the direction orthogonal to a rotor rotation center axis. It is a figure explaining the flow of the cooling oil when a rotor rotational speed is low. It is a figure explaining the flow of the cooling oil when a rotor rotational speed becomes high. It is a figure explaining the flow of the cooling oil when a rotor rotational speed becomes still higher. It is a figure explaining the change of the refrigerant | coolant delivery capability with respect to the change of a rotor rotational speed. In the rotary electric machine which concerns on embodiment of this invention, it is a figure which shows the relationship of the refrigerant | coolant delivery capability with respect to a rotor rotational speed. It is a figure explaining the flow of the cooling oil when a rotor rotational speed is low. It is a figure explaining the flow of the cooling oil when a rotor rotational speed becomes high. It is a figure explaining the flow of the cooling oil when a rotor rotational speed becomes still higher.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

  1 and 2 are diagrams showing a schematic configuration of a rotating electrical machine according to an embodiment of the present invention. FIG. 1 is a cross-sectional view of the stator 12 and the rotor 14 viewed from a direction orthogonal to the rotor rotation center axis (hereinafter simply referred to as the rotation center axis) 16a, and FIG. 2 is a rotor viewed from the direction orthogonal to the rotation center axis 16a. 14 and a sectional view of the rotor shaft 16 are shown. The rotating electrical machine according to the present embodiment includes a stator 12 whose rotation is fixed, a rotor 14 that can rotate relative to the stator 12, and a rotor shaft 16 that rotates together with the rotor 14, and a diameter that is orthogonal to the rotation center axis 16a. In the direction, the stator 12 and the rotor 14 are arranged to face each other with a predetermined minute gap, and the rotor 14 is arranged on the inner peripheral side of the stator 12.

  The rotor shaft 16 has a cylindrical shape in which a space 17 is formed. A rotor 14 is attached to the outer peripheral surface of the rotor shaft 16. The rotor 14 includes a rotor core 31 and a permanent magnet 32 disposed on the rotor core 31. The stator 12 includes a stator core 21 and a plurality of (for example, three-phase) coils 22 disposed on the stator core 21. A rotating magnetic field that rotates in the circumferential direction is formed in the stator 12 by passing an alternating current through a plurality of (three-phase) coils 22. The rotor 14 is rotated by applying torque (magnet torque) to the rotor 14 by electromagnetic interaction (attraction and repulsion) between the rotating magnetic field generated in the stator 12 and the field magnetic flux generated in the permanent magnet 32 of the rotor 14. Can be driven. In this manner, the rotating electrical machine can be caused to function as an electric motor that generates power in the rotor 14 using the power supplied to the coil 22. On the other hand, the rotating electrical machine can also function as a generator that generates power in the coil 22 using the power of the rotor 14.

  When torque (magnet torque) is applied between the stator 12 and the rotor 14, the permanent magnet 32 of the rotor 14 generates heat. Hereinafter, a configuration for cooling the rotor 14 (permanent magnet 32) will be described.

  A cooling flow path 34 is formed in the rotor 14 (rotor core 31) close to the permanent magnet 32. In the example shown in FIGS. 1 and 2, the cooling flow path 34 is formed in parallel with the rotation center axis 16a, and both ends of the cooling flow path 34 in the rotation center axis direction are open to the outside of the rotor.

  A cylindrical refrigerant supply shaft 46 is disposed in the internal space 17 of the rotor shaft 16 along the rotation center axis 16a. The rotation of the refrigerant supply shaft 46 is fixed. A refrigerant flow path 46a is formed inside the refrigerant supply shaft 46, and as shown by an arrow a in FIG. 3, cooling oil as a liquid refrigerant is supplied from a hydraulic source such as a hydraulic pump to the refrigerant flow path 46a. . The refrigerant supply shaft 46 is formed with a refrigerant discharge port 46b that communicates with the refrigerant flow channel 46a. As shown by an arrow b in FIG. 3, the cooling oil supplied to the refrigerant flow channel 46a flows from the refrigerant discharge port 46b. Discharge into the internal space 17 of the rotor shaft 16.

  In the rotor shaft 16 and the rotor 14 (rotor core 31), a plurality of communication channels 36-1 to 36-3 for communicating the internal space 17 of the rotor shaft 16 and the cooling channel 34 are formed in parallel to each other. Yes. Furthermore, a recess is formed in the inner peripheral surface of the rotor shaft 16 (the position where the communication channels 36-1 to 36-3 are formed), so that a plurality of communication channels 36-1 to 36-3 are formed. The refrigerant introduction port 38 is formed for introducing the cooling oil discharged from the refrigerant discharge port 46b of the refrigerant supply shaft 46 into the internal space 17 of the rotor shaft 16 into the communication flow paths 36-1 to 36-3. Yes. The refrigerant discharge port 46 b of the refrigerant supply shaft 46 is disposed to face the refrigerant introduction port 38 in the radial direction. In the example shown in FIGS. 1 and 2, the communication channels 36-1 to 36-3 are formed along the radial direction, and the radially inner ends of the communication channels 36-1 to 36-3 are the refrigerant inlets. 38, the radially outer ends of the communication channels 36-1 to 36-3 communicate with the cooling channel 34. A plurality of communication channels 36-1 to 36-3 are arranged at intervals from each other in the direction of the rotation center axis.

  In the present embodiment, the depth of the recess formed in the inner peripheral surface of the rotor shaft 16 changes in a stepwise manner in a plurality of ways. In other words, the inner diameter of the inner peripheral surface of the rotor shaft at the position where the refrigerant introduction port 38 is formed changes stepwise in a plurality of ways. In the example shown in FIGS. 1 and 2, the inner diameter (the depth of the recess) of the inner peripheral surface of the rotor shaft at the position where the refrigerant introduction port 38 is formed changes in three ways (three steps) in the direction of the rotation center axis. Yes. The portion 38a having the maximum inner diameter of the rotor shaft inner peripheral surface in the refrigerant introduction port 38 communicates with the communication flow path 36-1, and the portion 38c having the minimum inner diameter of the rotor shaft inner peripheral surface in the refrigerant introduction port 38 is formed. A portion 38b in which the inner diameter of the inner peripheral surface of the rotor shaft in the refrigerant introduction port 38 is between the maximum and minimum is in communication with the communication channel 36-2. Therefore, the radially inner end portion of the communication flow path 36-1 is positioned on the radially outer side than the radial inner end portion of the communication flow path 36-2, and the communication flow path 36-1 and the refrigerant introduction port 38 are connected to each other. The distance with respect to the rotation center axis 16a of the communication part 39-1 is larger than the distance with respect to the rotation center axis 16a of the communication part 39-2 between the communication flow path 36-2 and the refrigerant introduction port 38. And the radial direction inner side edge part of the communication flow path 36-3 is located in a radial direction inner side rather than the radial direction inner side edge part of the communication flow path 36-2, and the communication flow path 36-3 and the refrigerant | coolant introduction port 38 are between. The distance with respect to the rotation center axis 16a of the communication part 39-3 is smaller than the distance with respect to the rotation center axis 16a of the communication part 39-2 between the communication flow path 36-2 and the refrigerant introduction port 38. As described above, the distances of the communication portions 39-1 to 39-3 between the plurality of communication flow paths 36-1 to 36-3 and the refrigerant inlet 38 with respect to the rotation center axis 16a are plural (see FIGS. 1 and 2). In the example, it changes to 3 levels). The refrigerant discharge port 46b of the refrigerant supply shaft 46 is disposed at a position facing the portion 38a having the maximum inner diameter of the inner peripheral surface of the rotor shaft in the refrigerant introduction port 38 in the radial direction, and further communicates with the refrigerant introduction port 38 and the communication channel. It is preferable to arrange | position in the position which opposes the communication part 39-1 with 36-1, and radial direction.

  The cooling oil discharged from the refrigerant discharge port 46b of the refrigerant supply shaft 46 to the internal space 17 of the rotor shaft 16 is introduced into the refrigerant introduction port 38 by the centrifugal force generated by the rotation of the rotor shaft 16 and the rotor 14, and a plurality of communication channels are provided. It flows into the cooling flow path 34 through any of 36-1 to 36-3. As shown by the arrow d in FIG. 3, the cooling oil flows through the cooling flow path 34, whereby the rotor 14 (permanent magnet 32) is cooled. The cooling oil used for cooling the rotor 14 (permanent magnet 32) flows out of the rotor from both ends of the cooling flow path 34 in the rotation center axis direction.

  When the rotational speeds of the rotor shaft 16 and the rotor 14 are low, the centrifugal force acting on the cooling oil is small, and the ability to send the cooling oil from the refrigerant inlet 38 to the outside in the radial direction is reduced by the centrifugal force. As a result, the coolant oil level in the rotor shaft 16 (refrigerant inlet 38) is larger than the communication portion 39-3 between the refrigerant inlet 38 and the communication flow path 36-3, for example, as shown in FIG. This is the radially inner position. In that case, the cooling oil introduced into the refrigerant introduction port 38 from the refrigerant discharge port 46b passes through each of the communication channels 36-1 to 36-3 as shown by an arrow c in FIG. Flow into.

  When the rotational speeds of the rotor shaft 16 and the rotor 14 increase, the centrifugal force acting on the cooling oil increases, and the ability to send the cooling oil from the refrigerant inlet 38 to the radially outer side by the centrifugal force increases. As a result, the coolant oil level at the refrigerant inlet 38 changes radially outward, for example, as shown in FIG. 4B, than the communication portion 39-3 between the refrigerant inlet 38 and the communication flow path 36-3. The position is on the radially outer side and on the radially inner side of the communication portion 39-2 between the refrigerant introduction port 38 and the communication flow path 36-2. In that case, the cooling oil introduced into the refrigerant introduction port 38 from the refrigerant discharge port 46b does not pass through the communication flow channel 36-3 as shown by an arrow c in FIG. -2 flows into the cooling flow path 34.

  When the rotational speeds of the rotor shaft 16 and the rotor 14 are further increased and the centrifugal force acting on the cooling oil is further increased, the ability to send the cooling oil from the refrigerant introduction port 38 to the radially outer side is further increased by the centrifugal force. As a result, the coolant oil level at the refrigerant inlet 38 further changes radially outward, such as from a communication portion 39-2 between the refrigerant inlet 38 and the communication flow path 36-2 as shown in FIG. Is also positioned radially outside. In this case, the cooling oil introduced from the refrigerant discharge port 46b to the refrigerant introduction port 38 does not pass through the communication channels 36-2 and 36-3 as shown by the arrow c in FIG. -1 and flows into the cooling flow path 34. Thus, as the rotational speeds of the rotor shaft 16 and the rotor 14 increase, the coolant oil level in the rotor shaft 16 (refrigerant inlet 38) changes from A in FIG. 3 to B in FIG. 4 to C in FIG. The communication flow path that changes when the cooling oil flows into the cooling flow path 34 is changed from the communication flow paths 36-1 to 36-3 → the communication flow paths 36-1 and 36-2 → the communication flow path. It changes to 36-1 and the number of communication channels through which the cooling oil passes decreases.

  When the rotor rotational speed is low, the ability to send the cooling oil to the cooling flow path 34 due to centrifugal force tends to decrease. The amount of cooling oil delivered from the internal space 17 of the rotor shaft 16 to the cooling flow path 34 is lower than the amount of cooling oil supplied from the refrigerant discharge port 46b of the refrigerant supply shaft 46 to the internal space 17 of the rotor shaft 16. If it passes, the cooling capacity of the rotor 14 (permanent magnet 32) by the cooling oil is insufficient and the temperature rises, as shown at the time of low rotation in FIG. Further, the cooling oil accumulated in the internal space 17 of the rotor shaft 16 leaks to the outside of the rotor shaft, causing drag loss. On the other hand, in the present embodiment, when the rotor rotational speed is low, the number of communication passages through which the cooling oil flows into the cooling passage 34 from the refrigerant introduction port 38 increases. A decrease in the amount of cooling oil delivered to the cooling channel 34 can be suppressed. Therefore, as shown at the time of low rotation in FIG. 7, it is possible to prevent a rise in temperature by suppressing a decrease in the cooling capacity of the rotor 14 (permanent magnet 32) due to insufficient cooling oil delivery capacity to the cooling flow path 34. Further, it is possible to suppress the cooling oil accumulated in the internal space 17 of the rotor shaft 16 from leaking to the outside of the rotor shaft, and to suppress drag loss.

  On the other hand, when the rotor rotational speed is high, the ability to send the cooling oil to the cooling flow path 34 by centrifugal force tends to become excessively high. The cooling oil supply capability from the internal space 17 of the rotor shaft 16 to the cooling flow path 34 is higher than the supply capability of the cooling oil from the refrigerant discharge port 46b of the refrigerant supply shaft 46 to the internal space 17 of the rotor shaft 16. If it passes, the cooling oil is insufficient in the internal space 17 of the rotor shaft 16 and aeration occurs. When aeration occurs, drag loss due to foaming of the cooling oil occurs, and the cooling capacity of the rotor 14 (permanent magnet 32) by the cooling oil decreases as shown at the time of high rotation in FIG. On the other hand, in the present embodiment, when the rotor rotational speed is high, the number of communication flow paths through which the cooling oil flows from the refrigerant introduction port 38 to the cooling flow path 34 decreases. An excessive increase in the amount of cooling oil delivered to the cooling flow path 34 can be suppressed. Therefore, the occurrence of aeration due to the lack of cooling oil in the internal space 17 of the rotor shaft 16 can be suppressed, and the rotor 14 (permanent magnet 32) of the cooling oil bubbling is caused as shown in FIG. A decrease in cooling capacity and drag loss can be suppressed.

  Thus, in this embodiment, when the rotor rotational speed is low and the centrifugal force is small, the number of communication passages through which the cooling oil flows into the cooling passage 34 is increased, and the rotor rotational speed is high and the centrifugal force is increased. Is large, the number of communication channels through which the cooling oil flows into the cooling channel 34 is reduced. As a result, as shown in FIG. 7, the ability to send the cooling oil to the cooling flow path 34 can always be properly maintained regardless of the rotor rotational speed (centrifugal force), and varies according to the rotor rotational speed. Can be suppressed. As a result, the cooling capacity of the rotor 14 (permanent magnet 32) by the cooling oil can be always properly maintained regardless of the rotor rotational speed, and fluctuations according to the rotor rotational speed can be suppressed. Furthermore, drag loss due to leakage of cooling oil to the outside of the rotor shaft and generation of aeration due to insufficient cooling oil in the internal space 17 of the rotor shaft 16 can be suppressed.

  Further, in the present embodiment, the distances of the communication portions 39-1 to 39-3 between the plurality of communication flow paths 36-1 to 36-3 and the refrigerant introduction port 38 are changed in a plurality of ways. The inner diameter of the inner peripheral surface of the rotor shaft at the position where the refrigerant introduction port 38 is formed is changed in a plurality of ways. As a result, the number of communication flow paths through which the cooling oil flows into the cooling flow path 34 can be reduced with respect to an increase in rotor rotational speed (centrifugal force) with a simple configuration without using a variable mechanism. it can. Further, by disposing the refrigerant discharge port 46b of the refrigerant supply shaft 46 in a position facing the portion 38a having the maximum inner diameter of the inner surface of the rotor shaft in the refrigerant introduction port 38 in the radial direction, the rotor rotational speed is high. The communication channel through which the cooling oil passes can be surely limited to the communication channel 36-1.

  In the above embodiment, the case where the rotation of the refrigerant supply shaft 46 is fixed has been described, but the refrigerant supply shaft 46 may be rotating.

  In the present embodiment, for example, also with the configuration shown in FIG. 8, the number of communication channels through which the cooling oil flows into the cooling channel 34 is reduced with respect to an increase in the rotor rotational speed (centrifugal force). It is also possible. In the configuration example shown in FIG. 8, the piston 52 is disposed in the internal space 17 of the rotor shaft 16. The piston 52 is slidable in the radial direction with respect to the refrigerant supply shaft 46, and a biasing force is applied to the inside in the radial direction by the spring 53. Protruding portions 52c and 52d are provided on the upper surface (radially outer end surface) 52a of the piston 52, and the height of the protruding portion 52d is higher than the height of the protruding portion 52c. The protrusion 52d faces the communication channel 36-3 in the radial direction, and the projection 52c faces the communication channel 36-2 in the radial direction. The lower surface (radial inner end surface) 52b of the piston 52 faces the refrigerant flow path 46a. The refrigerant supply shaft 46 and the piston 52 rotate at the same rotational speed together with the rotor shaft 16 and the rotor 14.

  When the rotor rotational speed is low, the radially outward load acting on the lower surface 52b of the piston 52 due to the centrifugal force of the cooling oil is small, and the piston 52 is attached radially inward by the spring 53 as shown in FIG. The refrigerant discharge port 46b of the refrigerant supply shaft 46 is in communication with the communication flow paths 36-1 to 36-3. In that case, the cooling oil discharged from the refrigerant discharge port 46b flows into the cooling flow path 34 through each of the communication flow paths 36-1 to 36-3 as indicated by an arrow c in FIG.

  As the rotor rotational speed increases, the radially outward load acting on the lower surface 52b of the piston 52 increases due to the centrifugal force of the cooling oil, and the piston 52 slides radially outward as shown in FIG. Since the communication flow path 36-3 is closed by the part 52d, the refrigerant discharge port 46b does not communicate with the communication flow path 36-3 and communicates with the communication flow paths 36-1 and 36-2. In this case, the cooling oil discharged from the refrigerant discharge port 46b does not pass through the communication flow path 36-3 but passes through the communication flow paths 36-1 and 36-2 as shown by an arrow c in FIG. And flows into the cooling flow path 34.

  When the rotor rotational speed is further increased, the radially outward load acting on the piston 52 due to centrifugal force is further increased, and the piston 52 is further slid radially outward as shown in FIG. By closing the communication flow path 36-2, the refrigerant discharge port 46b does not communicate with the communication flow paths 36-2 and 36-3 and communicates with the communication flow path 36-1. In that case, the cooling oil discharged from the refrigerant discharge port 46b is cooled not through the communication flow paths 36-2 and 36-3 but through the communication flow path 36-1 as shown by the arrow c in FIG. It flows into the flow path 34. As described above, even in the configuration example shown in FIG. 8, the communication flow path through which the cooling oil flows into the cooling flow path 34 as the rotor rotational speed increases becomes the communication flow paths 36-1 to 36-3 → The communication flow paths 36-1 and 36-2 are changed to the communication flow path 36-1, and the number of communication flow paths through which the cooling oil passes is reduced.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to such embodiment at all, and it can implement with a various form in the range which does not deviate from the summary of this invention. Of course.

  12 Stator, 14 Rotor, 16 Rotor shaft, 16a Rotation center axis, 17 Internal space, 21 Stator core, 22 Coil, 31 Rotor core, 32 Permanent magnet, 34 Cooling flow path, 36-1 to 36-3 Communication flow path, 38 Refrigerant Inlet port, 39-1 to 39-3 communicating portion, 46 refrigerant supply shaft, 46a refrigerant channel, 46b refrigerant discharge port.

Claims (3)

A rotor shaft in which a space for supplying a liquid refrigerant is formed;
A rotor attached to the outer periphery of the rotor shaft and having a cooling flow path through which liquid refrigerant passes;
With
The rotor shaft and the rotor are formed with a plurality of communication channels for communicating the rotor shaft internal space and the rotor internal cooling channel,
The liquid refrigerant supplied to the inner space of the rotor shaft passes through the communication flow path by the rotation of the rotor shaft and the rotor so that the number of communication flow paths through which the liquid refrigerant passes decreases as the rotation speed of the rotor shaft and the rotor increases. The rotating electrical machine flows into the rotor internal cooling flow path. The rotating electrical machine according to claim 1,
A refrigerant supply member that supplies liquid refrigerant to the rotor shaft internal space is disposed in the rotor shaft internal space,
A refrigerant inlet for communicating with the plurality of communication channels and introducing the liquid refrigerant supplied from the refrigerant supply member into the communication channel is formed on the inner periphery of the rotor shaft,
The inner diameter of the inner periphery of the rotor shaft at the position where the refrigerant inlet is formed changes so that the distance between the communication portion of the plurality of communication channels and the refrigerant inlet varies with respect to the rotor rotation center axis in multiple ways. , Rotating electrical machinery. The rotating electrical machine according to claim 2,
A rotating electrical machine in which a coolant supply port of a coolant supply member is disposed at a position facing a portion in the coolant introduction port having a maximum inner diameter on the inner periphery of the rotor shaft in the radial direction.

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