Rotor structure

Abstract

Provided is a rotor structure including a rotor shaft S formed of a tubular outer shaft 3 including a plurality of magnets 1 arrayed on an outer peripheral surface and an inner shaft 4 inserted into an inside of the outer shaft 3 and provided with an outer tubular body 2 made of fiber-reinforced plastic and fitted to outer peripheries of the magnets 1, the inner shaft 4 and the outer shaft 3 being joined through interference fit. This rotor structure achieves application of sufficient pretention to the outer tubular body 2.

Description

Rotor Structure

[0001] The present invention relates to a rotor structure used in a rotating electrical machine such as a motor or a generator.

[0002] A conventional rotor structure is described, for example, in Patent Document 1. Patent Document 1 discloses a rotor structure in which a plurality of permanent magnets are arranged on the outer periphery of a shaft via a cylindrical member, and an outer cylinder made of carbon fiber reinforced plastic is provided on the outer surface of the arranged permanent magnets. This rotor structure, together with a stator arranged on the outer periphery thereof, constitutes a motor.

[0003] Japanese Patent Application Publication No. 2001-078378

[0004] However, in a rotor structure like the one described above, large centrifugal forces are generated on the magnets due to the larger magnets and higher rotational speeds that accompany higher torque motors, so it is necessary to generate pretension in the outer cylinder that exceeds this centrifugal force to adequately hold the magnets in place during high rotational speeds. Increasing the interference between the outer cylinder and the magnets is an effective way to apply pretension to the outer cylinder, but when a prefabricated cylinder is fitted around the outside of an array of magnets, the interference is limited to a small amount for assembly reasons.

[0005] On the other hand, there is a method of winding the reinforcing fibers around the magnet while applying high tension to them, but there is a possibility that the tension will be lost due to loosening of the fibers during winding or shrinkage of the resin when it hardens. For this reason, in conventional rotor structures where an outer cylindrical body made of fiber-reinforced plastic is provided on the outside of the arranged magnets, there was a need for an improvement to apply pretension to the outer cylindrical body.

[0006] The present invention was made in consideration of the above-mentioned conventional situation, and aims to provide a rotor structure that can impart sufficient pretension to an outer cylindrical body made of fiber-reinforced plastic on the outside of arranged magnets.

[0007] The rotor structure according to the present invention comprises a cylindrical outer shaft having a plurality of magnets arranged on its outer circumferential surface, an inner shaft inserted inside the outer shaft, and an outer cylindrical body made of fiber-reinforced plastic fitted onto the outer periphery of the magnets. The rotor structure is characterized in that the inner shaft and the outer shaft are joined by an interference fit.

[0008] By adopting the above-described configuration, the rotor structure of the present invention can impart sufficient pretension to an outer cylinder made of fiber-reinforced plastic on the outside of the arranged magnets.

[0009] FIG. 1 is a perspective view of a rotor showing a first embodiment of a rotor structure according to the present invention. FIG. 2 is a cross-sectional view showing an outer shaft and an inner shaft before interference fitting. FIG. 3 is a cross-sectional view showing an outer shaft and an inner shaft after interference fitting. FIG. 4 is a cross-sectional view showing a second embodiment of a rotor structure according to the present invention. FIG. 5 is a cross-sectional view showing a third embodiment of a rotor structure according to the present invention. FIG. 6 is a cross-sectional view showing a fourth embodiment of a rotor structure according to the present invention. FIG. 7 is a cross-sectional view showing a fifth embodiment of a rotor structure according to the present invention. FIG. 8 is a cross-sectional view showing a main part of the rotor structure shown in FIG. 7. FIG. 8 is a front view of the rotor structure shown in FIG. 7 as seen from the axial direction. FIG. 9 is a cross-sectional view showing a sixth embodiment of a rotor structure according to the present invention.

[0010] 1 has a structure in which a plurality of magnets 1 are arranged along the circumferential direction on the outer peripheral surface of a rotor shaft S, and an outer cylindrical body 2 made of fiber-reinforced plastic is fitted around the outer periphery of the arranged magnets 1. The magnets 1 are permanent magnets, and have a length equivalent to the overall axial length of the rotor R. The rotor R, together with a stator (not shown) arranged on the outside thereof, constitutes a rotating electric machine such as a motor or a generator.

[0011] For example, carbon fiber reinforced plastic (CFRP) using carbon fibers as reinforcing fibers is used for the outer cylinder 2. The reinforcing fibers used and the manufacturing method for the outer cylinder 2 are not limited, but examples include a method of laminating reinforcing fiber cloth and a method of winding continuous reinforcing fibers.

[0012] 2, the rotor shaft S includes a cylindrical outer shaft 3 having a plurality of magnets 1 arranged on its outer peripheral surface, and an inner shaft 4 inserted inside the outer shaft 3. The outer shaft 3 in the illustrated example is cylindrical and has an axial length that is approximately the same as the dimension of the rotor R in the axial direction.

[0013] On the other hand, the inner shaft 4 in the illustrated example has a central shaft portion 4A and an outer cylindrical portion 4B arranged coaxially, and is provided with a rib 4C connecting the shaft portion 4A and the cylindrical portion 4B. The cylindrical portion 4B is a portion that will later be tightly fitted inside the outer shaft 3, and in a more preferred embodiment, the axial length of the cylindrical portion 4B can be made longer than the axial length of the outer shaft 3. The rib 4C forms an annular shape that extends around the entire circumference of the shaft portion 4A and the cylindrical portion 4B, and although one rib is shown, multiple ribs can be provided, or lightening portions can be provided to reduce weight.

[0014] As shown in Figure 3, the outer shaft 3 and inner shaft 4 are joined by tightly fitting the cylindrical portion 4B of the inner shaft 4 inside the outer shaft 3, which has the magnet 1 and outer cylindrical body 2 attached. The outer shaft 3 and inner shaft 4 are made of materials with the same linear expansion coefficient, and in practice it is more preferable to use the same metallic material for both, specifically steel. Furthermore, since the two are joined by tight fitting, there is naturally an interference between the outer shaft 3 and the cylindrical portion 4B of the inner shaft 4.

[0015] Methods of interference fitting include press-fitting the inner shaft 4 into the outer shaft 3, press-fitting the inner shaft 4 into a preheated outer shaft 3, press-fitting a precooled inner shaft 4 into the outer shaft 3, and press-fitting a precooled inner shaft 4 into a preheated outer shaft 3.

[0016] In the rotor structure described above, both the outer shaft 3 and the inner shaft 4 are made of steel, allowing for a strong press fit. Also, chill fitting, in which the inner shaft 4 is kept at an extremely low temperature to allow it to shrink, is effective. Furthermore, chill shrink fitting, in which the outer shaft 3 to which the magnet 1 and outer cylindrical body 2 are assembled is heated and the inner shaft 4 is cooled, is also possible. While the fiber-reinforced plastic that forms the outer cylindrical body 2 has a small linear expansion coefficient, the outer shaft 3, which is made of steel, has a large linear expansion coefficient. Therefore, it is possible to heat and expand the outer shaft 3 to widen the fit gap during assembly.

[0017] In Figure 3, one end (left end) of the outer shaft 3 and the inner shaft 4 are aligned in the axial direction and are tightly fitted so that the other end of the inner shaft 4 extends from the other end of the outer shaft 3, but it is also acceptable for the inner shaft 4 to extend from both ends of the outer shaft 3.

[0018] The rotor structure having the above configuration applies sufficient pretension to the outer cylinder body 2 through the arranged magnets 1 by tightly fitting the inner shaft 4 onto the outer shaft 3, and in particular, pretension that exceeds the centrifugal force generated in the magnets 1 can be applied uniformly around the entire circumference of the outer cylinder body 2.

[0019] As a result, when the above rotor structure is applied to a motor, it applies pretension to the outer cylindrical body 2 that exceeds the centrifugal force generated in the magnet 1, so the rotor R does not expand at high rotation speeds, preventing abnormal noise due to poor balance. Also, the above rotor structure does not require widening the air gap with the stator to take into account the expansion of the rotor R, making it possible to achieve higher motor output and torque. Furthermore, the above rotor structure does not require a specific manufacturing method for the outer cylindrical body 2, so it is sufficient to manufacture the outer cylindrical body 2 using an appropriate method that takes into account strength, ease of assembly, etc., and it becomes possible to apply sufficient pretension to the outer cylindrical body 2.

[0020] Furthermore, in the rotor structure described above, the inner shaft 4 and the outer shaft 3 are made of materials with the same linear expansion coefficient, so that they expand and contract at the same rate in response to temperature changes, ensuring equal interference across the entire temperature range.

[0021] Furthermore, in the above rotor structure, it is necessary to expand the entire length of the outer shaft 3 in order to effectively increase the interference between the magnet 1 and the outer cylindrical body 2. Therefore, in the above rotor structure, the axial length of the cylindrical portion 4B of the inner shaft 4 is made longer than the axial length of the outer shaft 3, so that even if an assembly error occurs, the outer shaft 3 will be in close contact with the inner shaft 4 over its entire length and will expand in a manner that pushes it apart.

[0022] In the above rotor structure, if a process that generates a difference in temperature when the outer shaft 3 and the inner shaft 4 are interference-fitted is included, it is desirable that the linear expansion coefficients of the inner shaft 4 and the outer shaft 3 be the same, but they may have different linear expansion coefficients as long as there is no effect. It is also effective to provide a lead-in taper in the fitting portion of at least one of the inner shaft 4 and the outer shaft 3.

[0023] 4 to 10 are diagrams illustrating second to sixth embodiments of the rotor structure according to the present invention. In the following embodiments, the same components as those in the first embodiment are designated by the same reference numerals, and detailed descriptions thereof will be omitted.

[0024] 4 , an inner shaft 4 has a cylindrical portion 4B that is interference-fitted inside the outer shaft 3, and an outward flange portion 4F is provided at one axial end of the cylindrical portion 4B. In the rotor structure described above, the inner shaft 4 is placed on an assembly base 10 with the flange portion 4F facing downward, and the outer shaft 3 is interference-fitted.

[0025] The rotor structure described above can achieve the same effect as the first embodiment, and in addition, during the tight fit, the flange portion 4F serves as a positioning portion against which the lower end of the inner shaft 4 abuts against the base 10, allowing the inner shaft 4 to be stably fixed onto the base 10, so that the outer shaft 3 can be stably assembled to this inner shaft 4.

[0026] 5 shows a rotor structure in which the outer shaft 3 has an outward flange 3F at at least one of both axial ends. The outer shaft 3 in the illustrated example has the flange 3F at one end. In the rotor structure, the outer shaft 3 is placed on an assembly base 10 with the flange 3F facing downward, and the inner shaft 4 is tightly fitted thereto.

[0027] The rotor structure described above not only achieves the same effects as the first embodiment, but also serves as a positioning portion where the lower end of the outer shaft 3 abuts against the base 10 during interference fitting, allowing the outer shaft 3 to be stably fixed onto the base 10, thereby enabling the inner shaft 4 to be stably assembled to the outer shaft 3. Since the magnets 1 are attached to the outer shaft 3 from its radial direction, flanges 3F may be provided on both ends.

[0028] 6 , the inner shaft 4 has an outward flange 4F at one axial end of the cylindrical portion 4B, and the outer shaft 3 has a flange 3F at the other axial end. In the rotor structure described above, the outer shaft 3 is placed on an assembly base 10 with the flange 3F facing downward, and the inner shaft 4 is tightly fitted, with the flange 3F of the outer shaft 3 being pressed by a pressing jig 11.

[0029] The rotor structure described above can achieve the same effect as the first embodiment, and in addition, during the tight fit, the flange portion 4F serves as a positioning portion where the lower end of the inner shaft 4 abuts against the base 10, allowing the inner shaft 4 to be stably fixed onto the base 10, and the flange portion 3F of the outer shaft 3 serves as a pressure applying portion by the pressing jig 11, allowing the outer shaft 3 to be stably assembled to the inner shaft 4.

[0030] Fifth Embodiment The rotor structure shown in FIGS. 7 and 8 has a groove-shaped flow passage 5 extending along the axial direction on at least one of the inner periphery of the outer shaft 3 and the outer periphery of the inner shaft 4. In the illustrated example, the flow passage 5 is formed on the inner periphery of the outer shaft 3.

[0031] In addition, in the rotor structure described above, the inner shaft 4 has a cylindrical portion 4B that is tightly fitted inside the outer shaft 3, and has an outward flange portion 4F at one axial end of the cylindrical portion (the right end in Figure 7).

[0032] The rotor structure has an inlet 5A at the other end of the cylindrical portion 4B (the left end in Figure 7) that connects to the flow passage 5 from the inside of the cylindrical portion 4B, and an outlet 5B at the flange portion 4F of the cylindrical portion 4B that connects to the flow passage 5 and is open in the axial direction.

[0033] 9, the rotor structure has a plurality of flow passages 5 formed parallel to one another at equal intervals along the circumferential direction, and each flow passage 5 is disposed along the axial center line of each of the plurality of magnets 1 arranged on the outer peripheral surface of the outer shaft 3. In other words, the same number of flow passages 5 as the number of magnets 1 are formed.

[0034] The inlet 5A and outlet 5B may be disposed in each of the flow passages 5, or, for example, a circumferential flow passage that is connected to all of the flow passages 5 may be formed at both ends of the flow passage 5, and the inlet 5A and outlet 5B may be disposed at multiple locations in the circumferential flow passage.

[0035] The rotor structure described above can obtain the same effects as the first embodiment, and can also cool the magnets 1 by circulating a cooling fluid such as cooling oil through the flow passages 5 formed on the inner periphery of the outer shaft 3. Furthermore, the rotor structure described above forms groove-shaped flow passages 5 on at least one of the inner periphery of the outer shaft 3 and the outer periphery of the inner shaft 4, so that each magnet 1 and the outer shaft 3 come into contact over the entire circumference, making it possible to uniformly distribute the surface pressure.

[0036] Furthermore, the above rotor structure has an inlet 5A at one end of the flow passage 5 and an outlet 5B at the other end, so that, as shown by the arrows in Figures 7 and 8, the cooling fluid supplied to the inside of the inner shaft 4 is introduced into the flow passage 5 from the inlet 5A and discharged from the outlet 5B. The discharged cooling fluid is scattered toward the stator by centrifugal force and is used to cool the coils, etc. The above rotor structure can provide the inlet 5A and outlet 5B in the rotor shaft S consisting of the outer shaft 3 and inner shaft 4 without using end plates or the like to be placed at the ends of the magnets 1, which can also contribute to simplifying the structure.

[0037] Furthermore, the rotor structure described above has flow passages 5 along the center lines in the axial direction for each of the plurality of magnets 1, so that all of the magnets 1 can be cooled effectively.

[0038] <Sixth embodiment> In the rotor structure shown in Figure 10, the outer shaft 3 has an outward flange portion 3F on at least one of both axial ends, and an end plate 6 made of a non-magnetic material is interposed between the flange portion 3F and the end face of the magnet 1.

[0039] In addition, the rotor structure described above is configured such that the end plate 6 has a press-fit groove 7 on its outer periphery, and the ends of the reinforcing fibers F extending from the outer tubular body 2 are press-fitted between the flange portion 3F and the end plate 6 through the press-fit groove 7. In a more preferred embodiment, the flange portion 3F has an outer diameter dimension that corresponds at least to the outer diameter dimension of the outer tubular body 2.

[0040] The rotor structure described above can achieve the same effects as the first embodiment, and can maintain the ends of each magnet 1 in a fixed position by the flanges 3F and end plates 6. Furthermore, when the outer cylinder 2 is formed by wrapping reinforcing fibers around the outer periphery of the magnet 1, the rotor structure described above can effectively hold the ends of the stacked reinforcing fibers by the flanges 3F and end plates 6.

[0041] Furthermore, in the rotor structure described above, the ends of the reinforcing fibers F are press-fitted between the flange portion 3F and the end plate 6, and more preferably, the ends of the reinforcing fibers F are passed through the press-fit grooves 7 and press-fitted between the flange portion 3F and the end plate 6, thereby enabling a neat finish to the end of the outer tubular body 2. In this way, neatly finishing the end of the outer tubular body 2 is extremely effective in improving the quality of the rotor structure and workability in the subsequent assembly process.

[0042] Furthermore, the rotor structure described above can reliably achieve the above-described function of retaining the magnet 1 and the function of holding the laminated reinforcing fibers by making the outer diameter of the flange portion 3F the same as or larger than the outer diameter of the outer cylinder 2. Note that while Figure 10 illustrates a configuration in which the flange portion 3F and end plate 6 are disposed at one end of the outer shaft 3, it is of course also possible to place the flange portion 3F and end plate 6 at both ends of the outer shaft 3, which can further improve the function of retaining the magnet 1 and the function of holding the laminated reinforcing fibers.

[0043] 2 and 3 was fabricated. First, the outer shaft 3, the magnets 1, and the fiber-reinforced plastic outer cylindrical body 2 were assembled. Taking a design requiring an interference of 0.5 mm between the outer cylindrical body 2 and the magnet 1 as an example, if the construction limit for the interference is 0.3 mm when the outer cylindrical body 2 is attached to the outer shaft 3, by tightly fitting the inner ring 4 and outer ring 3 with an interference of just over 0.2 mm, it becomes possible to expand the outer ring 3 and increase the interference with the outer cylindrical body 2.

[0044] If the outer diameter of the inner shaft 4 is 100 mm, it is necessary to provide an interference of 0.2% with the outer shaft 3. Because the linear expansion coefficient of iron is approximately 1.2E-5, it is necessary to maintain a temperature difference of 166 K when fitting the inner shaft 4 into the outer shaft 3 at room temperature, but this temperature difference can be created by cooling the inner shaft 4 with liquid nitrogen. Alternatively, the above temperature difference can be achieved by heating the outer shaft 3, to which the magnet 1 and outer cylindrical body 2 are attached, to approximately 125°C and cooling the inner shaft 4 to approximately -40°C.

[0045] The detailed configuration of the rotor structure according to the present invention is not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the present invention, and the configurations of the above-described embodiments can also be combined.

[0046] R rotor S rotor shaft 1 magnet 2 outer cylinder 3 outer shaft 3F flange portion 4 inner shaft 4B cylindrical portion 4F flange portion 5 flow passage 5A inlet 5B outlet 6 end plate 7 press-fit groove

Claims

1. A rotor structure in which a rotor shaft is formed by a cylindrical outer shaft with multiple magnets arranged on its outer surface and an inner shaft inserted inside the outer shaft, and an outer cylinder made of fiber-reinforced plastic is fitted onto the outer periphery of the magnets, the inner shaft and the outer shaft being joined by an interference fit.

2. A rotor structure according to claim 1, wherein said inner shaft and said outer shaft are made of materials having the same linear expansion coefficient.

3. A rotor structure as described in claim 1 or 2, characterized in that the inner shaft has a cylindrical portion that is tightly fitted inside the outer shaft, and the axial length of the cylindrical portion is greater than the axial length of the outer shaft.

4. A rotor structure as claimed in claim 1 or 2, characterized in that the inner shaft has a cylindrical portion which is tightly fitted inside the outer shaft, and an outward flange portion is provided at one axial end of the cylindrical portion.

5. A rotor structure according to claim 1 or 2, characterized in that the outer shaft has an outward flange portion at least on one of both axial ends.

6. A rotor structure according to claim 4, characterized in that said cylindrical portion of said outer shaft has an outward flange portion at least at one of both axial ends.

7. A rotor structure according to claim 1 or 2, characterized in that at least one of the inner periphery of the outer shaft and the outer periphery of the inner shaft has a groove-like flow passage extending along the axial direction.

8. A rotor structure as described in claim 7, characterized in that the inner shaft has a cylindrical portion that is tightly fitted inside the outer shaft, and has an outward flange portion at one axial end of the cylindrical portion, and has an inlet port at the other end side of the cylindrical portion that connects to the flow passage from the inside of the cylindrical portion, and has an outlet port in the flange portion of the cylindrical portion that connects to the flow passage and is open in the axial direction.

9. A rotor structure according to claim 7, characterized in that the flow passages are arranged along the center lines in the axial direction of each of the magnets arranged on the outer circumferential surface of the outer shaft.

10. A rotor structure as described in claim 1 or 2, characterized in that the outer shaft has an outward flange portion on at least one of both axial ends, and an end plate is interposed between the flange portion and the end face of the magnet.

11. A rotor structure according to claim 10, characterized in that an end of a reinforcing fiber extending from said outer cylinder body is press-fitted between said flange portion and said end plate.

12. A rotor structure as described in claim 11, characterized in that the end plate has a press-fit groove on its outer periphery, and the ends of reinforcing fibers extending from the outer cylinder are pressed into between the flange portion and the end plate through the press-fit groove.

13. The rotor structure according to claim 10, wherein the flange portion has an outer diameter dimension at least equivalent to the outer diameter dimension of the outer cylinder body.

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