Rotor shaft

Abstract

An ebullient cooling type rotor shaft according to the present invention is inserted through the axial center of a rotor core, is supported by two bearings, and rotates integrally with the rotor core.　It is also possible to provide the ebullient cooling type rotor shaft having stable and high cooling performance that has a sealed space filled with refrigerant extending from the insertion part surrounded by the rotor core to the shaft end part outside the rotor core. The inner diameter of the sealed space is larger at the insertion part than at the shaft end part, with a lattice structure formed in the entire sealed space. The refrigerant is cooled and condensed by a cooling unit formed at least at one of the shaft end parts, and it is therefore possible to separate the condensation point and the boiling point of the refrigerant.

Description

Technical Field

[0001] The present invention relates to a rotor shaft, and more particularly to a rotor shaft that is inserted into a rotor of an electric motor and used as an output shaft.

Background Art

[0002] An electric motor generates heat due to losses that occur when converting electrical energy into mechanical energy, and the permanent magnets provided in the electric motor are demagnetized due to a temperature rise, so cooling is necessary.

[0003] As a cooling method for an electric motor, a boiling cooling method that utilizes the latent heat associated with the phase change of a refrigerant is known. In Patent Document 1, a refrigerant liquid is enclosed in a hollow rotor shaft, and the refrigerant is boiled on the inner surface of the rotor shaft, and cooling is performed by the latent heat of evaporation at this time.

[0004] In what is described in Patent Document 1, grooves extending in the axial direction formed on the inner surface of the rotor shaft lift and flow down the refrigerant liquid accumulated at the lower part due to the rotation of the rotor shaft, and a thin film of the refrigerant liquid is formed on the groove surface, and evaporation is promoted to prevent overheating of the electric motor.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in what is described in Patent Document 1, the refrigerant liquid accumulates in the lower part of the rotor shaft, and since the grooves are completely submerged in this refrigerant liquid pool, a thin film of the refrigerant liquid is not formed in this part, and the heat transfer promotion effect due to an increase in the evaporation area is lost, so the heat transfer promotion effect due to forming the grooves is diminished.

[0007] The present invention has been made in view of the problems of the prior art, and its objective is to provide a boiling-cooled rotor shaft that prevents the heat transfer promoting effect by the formation of a thin film of refrigerant liquid from being reduced by refrigerant liquid accumulation, and that can stably obtain high cooling performance. [Means for solving the problem]

[0008] The inventors of the present invention have conducted extensive research to achieve the above objectives and have found that these objectives can be achieved by separating the condensation and boiling points of the refrigerant within the rotor shaft and forming a lattice structure throughout the entire sealed space inside the rotor shaft, thereby completing the present invention.

[0009] In other words, the boiling-cooled rotor shaft of the present invention is inserted through the axial center of the rotor core, supported by two bearings, and rotates integrally with the rotor core. Furthermore, the device has a sealed space filled with a refrigerant extending from the insertion portion surrounded by the rotor core to the shaft end outside the rotor core, the inner diameter of the sealed space is larger in the insertion portion than in the shaft end, a lattice structure is formed throughout the sealed space, and the refrigerant is cooled and condensed in a cooling portion formed on at least one of the shaft ends. [Effects of the Invention]

[0010] According to the present invention, the refrigerant is condensed at the shaft end of the rotor shaft and supplied to the insertion section, making it difficult for refrigerant to accumulate in the insertion section. In addition, a lattice structure is formed throughout the sealed space, preventing the loss of the heat transfer promoting effect due to refrigerant accumulation, thus providing a boiling-cooled rotor shaft with stable and high cooling performance. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view showing an example of a boiling-cooled rotor shaft of the present invention. [Figure 2]This is a cross-sectional view showing an example of a boiling-cooled rotor shaft having orifice plates at the cooling section inlet and outlet. [Figure 3] Figure 2 shows an example of an orifice plate in cross-section AA. [Figure 4] This is a cross-sectional view showing an example of a boiling-cooled rotor shaft having a refrigerant liquid supply channel. [Figure 5] This is a cross-sectional view showing an example of a boiling-cooled rotor shaft with a centrifugal pump. [Figure 6] Figure 5 shows an example of a centrifugal pump in cross-section AA. [Figure 7] This is a cross-sectional view showing an example of a boiling-cooled rotor shaft having a refrigerant liquid supply channel extending to the other end of the shaft. [Modes for carrying out the invention]

[0012] The boiling-cooled rotor shaft of the present invention will be described in detail. The rotor shaft of the present invention is a hollow rotor shaft having a sealed space inside, which is inserted through the axial center of the rotor core and supported by two bearings, and rotates integrally with the rotor core.

[0013] As shown in Figure 1, the above-mentioned sealed space is formed continuously from the insertion portion surrounded by the rotor core to the shaft end protruding outside the rotor core, and the inner diameter of the sealed space is larger in the insertion portion than in the shaft end. A refrigerant is sealed within this sealed space.

[0014] At least one end of the shaft has a cooling section that removes heat from the outside. As shown by the arrow in Figure 1, the refrigerant gas evaporated in the insertion section by the heat from the rotor core is cooled in the cooling section and condenses into a refrigerant liquid.

[0015] The refrigerant liquid generated in the cooling section rotates along with the rotor shaft due to friction with the inner surface of the rotor shaft, thus acting as a centrifugal force on the refrigerant liquid. This centrifugal force causes the refrigerant liquid to be supplied from the small-diameter shaft end to the large-diameter insertion section, as shown by the arrow in Figure 1.

[0016] Thus, in the boiling-cooled rotor shaft of the present invention, since the evaporation location and the condensation location of the refrigerant are separated in the axial direction, it is difficult for a refrigerant liquid pool to be formed in the insertion portion, which is the evaporation location of the refrigerant.

[0017] Furthermore, a lattice structure is formed throughout the sealed space. The lattice structure has a structure in which lattices branched in a dendritic shape are arranged periodically, the branched lattices are connected to each other, and there are spaces between the lattices.

[0018] The lattice structure formed throughout this sealed space gets wet with the refrigerant liquid and forms a thin film of the refrigerant liquid, serving as fins that increase the evaporation area of the refrigerant liquid. Even if a refrigerant liquid pool is formed in the insertion portion, there will necessarily be a portion exposed above the refrigerant liquid pool, thus improving and stabilizing the cooling performance.

[0019] In addition, since the lattice structure has a structure in which the lattices branched in a dendritic shape as described above are connected to each other and there is a certain space between these lattices, weight reduction can be achieved and the rigidity per unit mass can also be increased.

[0020] Note that in the figure, in order to represent the flow of the refrigerant liquid, the refrigerant liquid is depicted between the rotor shaft and the lattice structure. However, the lattice structure is integrated with the outer shell of the rotor shaft, and the refrigerant liquid in the insertion portion forms a thin film on the surface of the lattice structure and the inner surface of the rotor shaft without forming a refrigerant liquid pool.

[0021] The above lattice structure can be formed by a 3D printer and can be integrally molded with the outer shell of the rotor shaft.

[0022] Also, since there are no restrictions in the construction method for the 3D printer, the outer diameter of the insertion portion can be increased, the heat transfer path from the rotor shaft to the permanent magnet provided in the rotor core can be shortened, and the permanent magnet of the rotor core can be efficiently cooled.

[0023] The materials used to construct the outer shell and lattice structure of the rotor shaft include steel, stainless steel, aluminum, titanium, copper, resin, and ceramics. Multiple types of these materials can be used in combination depending on the required strength, thermal conductivity, and other properties. Furthermore, metal and ceramic lattice structures can be formed using 3D printers employing methods such as laser sintering and laser melting.

[0024] The above-mentioned refrigerant can be sealed within a sealed space by providing a valve on the outer shell of the rotor shaft. In this case, it is preferable to reduce the pressure in the sealed space before sealing in the refrigerant.

[0025] By reducing the pressure in the sealed space, the boiling point of the refrigerant is lowered, improving cooling performance, and preventing the pressure inside the rotor shaft from becoming too high due to refrigerant boiling. The pressure in the sealed space is preferably between 0.1 and 10 atmospheres, although this depends on the type and amount of refrigerant.

[0026] As the refrigerant mentioned above, a refrigerant with a boiling point of 50-60°C at 1 atmosphere can be used, and examples include fluorine-based liquids such as hydrofluoroethers and fluoroketones.

[0027] The outer surface of the shaft end of the cooling unit described above preferably has fins from the viewpoint of improving cooling performance. The cooling method may be air cooling or liquid cooling, but a higher cooling effect can be obtained with liquid cooling.

[0028] A liquid-cooled cooling system can be formed by covering the shaft end with a case, flowing cooling water so that it contacts the outer surface of the shaft end, and sealing the gap between the case and the shaft end to prevent leakage of the cooling water outside the system. Although the figure shows an example where the cooling system is located at only one shaft end, cooling systems may be provided at both shaft ends.

[0029] The cooling section preferably regulates the amount of refrigerant supplied to the insertion section. As shown in Figure 2, an orifice plate is provided at the refrigerant inlet and outlet of the cooling section. Instead of supplying the refrigerant that has been cooled and condensed in the cooling section directly to the insertion section, a refrigerant reservoir is formed in the cooling section to store the refrigerant. This makes it difficult for a refrigerant reservoir to form in the insertion section, thus stabilizing the cooling performance.

[0030] As shown in Figure 3, the orifice plate has holes in the center and the periphery. With this shape, the refrigerant gas that boils in the insertion section enters the cooling section through the holes in the center and condenses, and the refrigerant liquid is supplied from the cooling section to the insertion section through the holes in the periphery.

[0031] The refrigerant liquid cooled in the above-mentioned cooling section may be supplied to the insertion section by flowing along the inner surface of the rotor shaft or the surface of the lattice structure. However, as shown in Figure 4, it is preferable to provide a refrigerant liquid supply channel that extends axially within the sealed space of the insertion section and supply the refrigerant liquid to the insertion section by flowing it axially through this refrigerant liquid supply channel.

[0032] By flowing the refrigerant liquid through a refrigerant liquid supply channel, flow resistance can be reduced. Since this refrigerant liquid supply channel extends axially within the sealed space of the insertion section, low-temperature refrigerant liquid can be supplied even to areas far from the cooling section of the insertion section. This prevents uneven cooling in the axial direction and improves cooling performance.

[0033] The refrigerant liquid supply passage described above connects to a hole in the peripheral edge of the orifice and is located on the outer diameter side of the inner circumferential surface of the cooling section. By providing the refrigerant liquid supply passage on the outer diameter side, centrifugal force is applied to the refrigerant liquid due to friction with the inner surface of the rotating rotor shaft, and this centrifugal force allows the refrigerant liquid to flow in the axial direction.

[0034] As described above, instead of applying centrifugal force to the refrigerant liquid solely through friction between the inner surface of the rotating rotor shaft and the refrigerant liquid, as shown in Figure 5, a centrifugal pump can be installed coaxially with the rotor shaft and integrated within the sealed space of the insertion section, and the refrigerant liquid can be pumped by the pump pressure of this centrifugal pump.

[0035] By providing a centrifugal pump connected to the holes at the periphery of the orifice plate mentioned above, it becomes possible to obtain stable cooling performance under a wider range of motor operating conditions.

[0036] In other words, if centrifugal force is applied to the refrigerant liquid solely by friction between the refrigerant liquid and the inner surface of the rotor shaft, the refrigerant liquid is also subject to inertial forces, and since the refrigerant liquid does not rotate in the same way as the rotor shaft, not all of the rotational force of the rotor shaft contributes to the centrifugal force acting on the refrigerant liquid.

[0037] In contrast, a centrifugal pump rotates the refrigerant liquid using its blades, just as it rotates the rotor shaft. As a result, all of the rotational force of the rotor shaft acts as centrifugal force on the refrigerant liquid.

[0038] Therefore, the flow rate of the refrigerant liquid can also be set by a centrifugal pump, increasing the design freedom for the pipe resistance of the orifice plate, i.e., the diameter of the holes at the periphery, and enabling stable cooling performance under a wider range of motor operating conditions.

[0039] Furthermore, as the rotational speed of the rotor shaft increases, the pump pressure of the centrifugal pump also increases, ensuring that the refrigerant liquid is reliably supplied to the insertion section and preventing dry-out of the insertion section. This makes it possible to reduce the amount of refrigerant sealed in the enclosed space, suppressing the accumulation of refrigerant liquid in the insertion section and further improving cooling performance.

[0040] In addition, the fact that the centrifugal pump is coaxial with and integrated with the rotor shaft offers advantages in terms of cost and weight reduction compared to having a separate pump.

[0041] As shown in Figure 6, the centrifugal pump, which is coaxial with and integrated with the rotor shaft, has a refrigerant gas passage in the center, and the axial tops of the blades are joined to the inner surface of the rotor shaft.

[0042] Furthermore, with a centrifugal pump, a greater centrifugal force is applied to the refrigerant liquid than the centrifugal force due to friction with the inner surface of the rotor shaft. As shown in Figure 7, it is possible to flow the refrigerant liquid from the outside towards the shaft center against the centrifugal force due to friction.

[0043] Furthermore, the portion of the refrigerant liquid supply channel that directs the refrigerant liquid from the outside towards the shaft center is designed to be a smooth, dish-like shape without blades or protrusions, excluding the refrigerant gas flow path, so that the rotational force of the rotor shaft is not forcibly transmitted to the refrigerant liquid.

[0044] Because the refrigerant liquid supply channel is connected to the centrifugal pump, as shown in Figure 7, the refrigerant liquid supply channel can be positioned at the axial center, and by supplying refrigerant liquid from this refrigerant liquid supply channel to the vicinity of the axial center of the insertion section, the evaporation area of ​​the refrigerant liquid can be further increased.

[0045] Furthermore, by extending the refrigerant liquid supply channel located at the center of the shaft to the sealed space at the other end of the shaft, the refrigerant liquid can also be supplied to the other end of the shaft to cool it.

[0046] Since the drive motor of an electric vehicle has its shaft end connected to the transmission shaft, the coolant liquid cooled at one shaft end can be circulated to the other shaft end connected to the transmission shaft, thereby cooling the transmission as well.

[0047] This suppresses the temperature rise of the gear teeth in the transmission, thereby improving pitching strength. Furthermore, in motors with integrated inverters, it becomes possible to reduce the amount of heat flowing into the inverter by suppressing the temperature rise of the transmission.

[0048] Since the rotor shaft of the present invention can be cooled from the inside of the rotor core, it can be suitably used as a rotor shaft for a surface magnet motor (SPM) that has permanent magnets on the outer diameter surface of the rotor core. [Explanation of symbols]

[0049] 1. Rotor shaft 11 Outer shell 12 Closed space 13 Lattice Structures 2 shaft end 21 Cooling section 22 fins 3 Insertion part 4 Refrigerant 41 Refrigerant liquid 42 Refrigerant gas 5 Orifice Plate 51. Central opening (refrigerant gas inlet) 52 Peripheral holes (refrigerant liquid outlet) 6. Centrifugal fan 61 feathers 62 Refrigerant gas flow path 7. Refrigerant liquid supply channel 100 rotor cores 200 bearing 300 stator 400 Cooling water 500 transmission

Claims

1. A rotor shaft that is inserted through the axial center of the rotor core, supported by two bearings, and rotates integrally with the rotor core, It has a sealed space filled with refrigerant, extending from the insertion portion surrounded by the rotor core to the shaft end outside the rotor core. The inner diameter of the above-mentioned sealed space is larger at the insertion point than at the shaft end. A lattice structure is formed throughout the entire sealed space described above. A boiling-cooled rotor shaft characterized in that the above-mentioned refrigerant is cooled and condensed in a cooling section formed on at least one of the shaft ends.

2. The above cooling unit has orifice plates at the inlet and outlet of the refrigerant, The boiling-cooled rotor shaft according to claim 1, characterized in that the orifice plate has holes in its central portion and peripheral portion.

3. The sealed space of the insertion portion is provided with a refrigerant liquid supply channel extending in the axial direction, The boiling-cooled rotor shaft according to claim 2, characterized in that the refrigerant liquid supply passage is provided on the outer diameter side of the inner surface of the cooling section and is connected to the hole in the peripheral portion to allow the condensed refrigerant liquid to flow in the axial direction.

4. Within the sealed space of the insertion portion described above, there is a centrifugal pump that is coaxial with and integrated with the rotor shaft. The boiling-cooled rotor shaft according to claim 2, characterized in that the centrifugal pump is connected to the hole in the peripheral portion.

5. The other end of the shaft is connected to the transmission shaft. The above centrifugal pump is equipped with a refrigerant liquid supply channel, The boiling-cooled rotor shaft according to claim 4, characterized in that the refrigerant liquid supply channel extends to the sealed space at the other end of the shaft.

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