JP7510055B2 - Eddy current reduction gear - Google Patents

Description

The present invention relates to an eddy current type reduction gear.

In recent years, large vehicles such as trucks and buses have begun to be equipped with eddy current reduction gears as auxiliary brakes (see, for example, Patent Document 1). These eddy current reduction gears include a rotor that is fixed to a rotating shaft such as the vehicle's propeller shaft or drive shaft, and a stator that is fixed to a non-rotating part such as the vehicle's transmission.

The rotor has an annular drum ring, and the stator has multiple permanent magnets and an annular casing cover that covers the multiple permanent magnets. The multiple permanent magnets are arranged radially inside the drum ring and are arranged along the circumferential direction of the drum ring. The casing cover has multiple pole pieces. The multiple pole pieces are arranged between the drum ring and the multiple permanent magnets and are arranged along the circumferential direction of the drum ring. The outer peripheral surface of the casing cover faces the inner peripheral surface of the drum ring. The circumferential arrangement positions of the multiple permanent magnets are switched by an actuator.

In this eddy current reduction gear device, the circumferential position of the multiple permanent magnets is switched by an actuator, and when adjacent permanent magnets are arranged so as to straddle the pole pieces, magnetic flux passes between the adjacent permanent magnets and the pole pieces, so no magnetic force acts on the drum ring. In this state, the eddy current reduction gear device is in a non-braking state, and no braking force is generated.

On the other hand, when the circumferential position of the multiple permanent magnets is switched by an actuator and each permanent magnet is arranged facing a pole piece, the magnetic flux between adjacent permanent magnets reaches the drum ring through the pole piece, and a magnetic force acts on the drum ring. When a magnetic force acts on the drum ring in this way, eddy currents are generated in the drum ring, and the interaction between this eddy current and the magnetic force causes a force (Lorentz force) to act on the drum ring in the opposite direction to the rotational direction. In this state, the eddy current reduction gear device is in a braking state and a braking force is generated.

JP 2018-207781 A

When the eddy current reduction gear is in a braking state and eddy currents are generated in the drum ring, the drum ring heats up due to Joule heat. Here, the inventors have discovered through various tests that when the drum ring heats up due to Joule heat, heat is concentrated in the axial center of the inner circumferential surface of the drum ring, and this axial center becomes the highest temperature.

The inventors also discovered that if the braking state of the eddy current reduction device continues and the drum ring continues to generate heat, the temperature of the axial center part of the inner surface of the drum ring will exceed the heat resistance temperature, and an oxide film will be formed in this axial center part due to high-temperature oxidation, and there is a risk that this oxide film will come into contact with the outer surface of the casing cover. The inventors then concluded that in order to suppress the formation of an oxide film due to high-temperature oxidation, it would be effective to suppress the rate of temperature rise in the axial center part of the inner surface of the drum ring.

Here, the inventors considered widening the gap between the inner surface of the drum ring and the outer surface of the casing cover in order to suppress the rate of temperature rise in the axial center of the inner surface of the drum ring. However, they concluded that doing so would reduce the magnetic flux reaching the drum ring, thereby reducing the braking torque of the eddy current reduction gear device. The inventors then thought that there was room for improvement in order to extend the braking time by suppressing the rate of temperature rise in the axial center of the inner surface of the drum ring while maintaining the braking torque.

The present invention was made based on the above findings, and aims to provide an eddy current reduction gear that can suppress the rate of temperature rise in the axial center of the inner peripheral surface of the drum ring, thereby extending the braking time, while ensuring braking torque.

The eddy current reduction gear according to the present invention comprises an annular drum ring, a plurality of permanent magnets arranged radially inside the drum ring and aligned along the circumferential direction of the drum ring, and an annular casing cover having a plurality of pole pieces arranged between the drum ring and the plurality of permanent magnets and aligned along the circumferential direction of the drum ring, the outer circumferential surface of which faces the inner circumferential surface of the drum ring. This eddy current reduction gear has at least one of a first groove formed in the axial center of the inner circumferential surface of the drum ring and forming an annular shape along the circumferential direction of the drum ring, and a second groove formed in the axial center of the outer circumferential surface of the casing cover and forming an annular shape along the circumferential direction of the casing cover.

According to the eddy current reduction gear device of the present invention, at least one of the first groove and the second groove widens the gap (air gap) between the axial center of the inner peripheral surface of the drum ring and the axial center of the outer peripheral surface of the casing cover, and the magnetic flux reaching the axial center of the inner peripheral surface of the drum ring is reduced. Therefore, on the inner peripheral surface of the drum ring, the magnetic flux is dispersed on both sides of the axial center, so the amount of heat generated by eddy currents in this axial center is suppressed. This suppresses the rate of temperature rise in the axial center of the inner peripheral surface of the drum ring (i.e., mitigates localized temperature rise), so the time it takes for the temperature of this axial center to reach the heat-resistant temperature can be extended, and thus the braking time can be extended.

Moreover, when the eddy current reduction gear has a first groove, this first groove is formed only in the axial center, which is a part of the inner peripheral surface of the drum ring. Therefore, the reduction in the magnetic flux reaching the drum ring can be minimized compared to, for example, the case where the position of the inner peripheral surface of the drum ring is moved back to the position of the bottom surface of the first groove, thereby widening the gap between the inner peripheral surface of the drum ring and the outer peripheral surface of the casing cover. This ensures that the magnetic force acting on the drum ring is secured, and therefore that the braking torque is secured.

Similarly, if the eddy current reduction gear has a second groove, this second groove is formed only in the axial center, which is a part of the outer peripheral surface of the casing cover. Therefore, the reduction in magnetic flux reaching the drum ring can be minimized compared to, for example, the case where the position of the outer peripheral surface of the casing cover is moved back to the position of the bottom surface of the second groove to increase the gap between the inner peripheral surface of the drum ring and the outer peripheral surface of the casing cover. This ensures that the magnetic force acting on the drum ring is secured, and therefore that braking torque is secured.

When the eddy current reduction gear has the first groove, it is preferable that the first groove is formed in a tapered shape in which the groove width increases toward the casing cover side.

When the first groove has a tapered shape, the cross-sectional shape of the corner on the opening side of the first groove is formed to have an obtuse angle. This prevents thermal stress from concentrating on the corner on the opening side of the first groove, and therefore prevents thermal fatigue cracks from occurring due to thermal cycles on the corner on the opening side of the first groove.

In the eddy current reduction gear, the first groove can have a bottom surface and a pair of side surfaces. In this case, the bottom surface is formed along the axial direction of the drum ring and faces the outer peripheral surface of the casing cover. It is preferable that the pair of side surfaces are formed in a tapered shape in which the distance between them increases toward the casing cover.

When the first groove has a pair of tapered side surfaces, eddy currents concentrate at the corners on the bottom side and the corners on the opening side of the first groove, and the current density increases at each side. Therefore, even if the gap (air gap) between the bottom surface of the first groove and the outer peripheral surface of the casing cover is widened, the decrease in braking torque can be suppressed. Therefore, the rate of temperature rise in the axial center of the inner peripheral surface of the drum ring can be effectively suppressed while maintaining braking torque.

When the eddy current reduction gear has the first groove, it is preferable that the inner peripheral surface of the drum ring has opposing surfaces on both sides of the first groove, the opposing surfaces including an area located within the length of the pole piece along the axial direction of the drum ring, and opposing the outer peripheral surface of the casing cover.

This configuration allows magnetic flux to pass between the pole piece and the drum ring through the opposing surface that is closer to the pole piece than the first groove. This ensures that the magnetic force acting on the drum ring is sufficient, and therefore the braking torque is sufficient.

The eddy current reduction gear may have a plurality of the first grooves. The plurality of first grooves are formed in a line in the axial direction of the drum ring.

When the eddy current reduction gear has multiple first grooves, a facing surface facing the pole piece is formed between the multiple first grooves, and magnetic flux can pass between the pole piece and the drum ring through this facing surface. This suppresses the rate of temperature rise in the axial center of the inner circumferential surface of the drum ring, while increasing the magnetic force acting on the drum ring compared to, for example, a case in which a single first groove is formed in the axial center of the inner circumferential surface of the drum ring, thereby improving the braking torque.

When the eddy current reduction gear has the second groove, it is preferable that the outer peripheral surface of the casing cover has opposing surfaces on both sides of the second groove, the opposing surfaces including an area located within the length of the pole piece along the axial direction of the drum ring, and opposing the inner peripheral surface of the drum ring.

This configuration allows magnetic flux to pass between the pole piece and the drum ring through the opposing surface that is located closer to the drum ring than the second groove. This ensures that the magnetic force acting on the drum ring is sufficient, and therefore the braking torque is sufficient.

The eddy current reduction gear may have a plurality of the second grooves. The plurality of second grooves are formed in a line in the axial direction of the casing cover.

When the eddy current reduction gear has multiple second grooves, an opposing surface facing the drum ring is formed between the multiple second grooves, and magnetic flux can pass between the pole piece and the drum ring through this opposing surface. This suppresses the rate of temperature rise in the axial center of the inner peripheral surface of the drum ring, while increasing the magnetic force acting on the drum ring compared to, for example, a case in which a single groove is formed in the axial center of the outer peripheral surface of the casing cover, thereby improving the braking torque.

According to the present invention, it is possible to extend the braking time by suppressing the rate of temperature rise in the axial center part of the inner peripheral surface of the drum ring while ensuring braking torque.

1 is an enlarged cross-sectional view of a main portion of an eddy current reduction gear according to a first embodiment of the present invention. FIG. 2 is a diagram illustrating how the eddy current reduction gear device shown in FIG. 1 is switched between a non-braking state and a braking state. FIG. 2 is a further enlarged view of a portion of an enlarged cross section of a main portion of the eddy current reduction gear device shown in FIG. 1 . FIG. 2 graphically illustrates test data illustrating the effectiveness of the grooves shown in FIG. 1 . FIG. 2 graphically illustrates test data illustrating the effectiveness of the grooves shown in FIG. 1 . FIG. 6 is an enlarged cross-sectional view of a main portion of an eddy current reduction gear device according to a reference example, among the eddy current reduction gear devices from which the test data shown in FIG. 5 was obtained. FIG. 4 is a cross-sectional view showing a first modified example of a groove in the first embodiment. FIG. 11 is a cross-sectional view showing a second modified example of the groove in the first embodiment. FIG. 11 is a cross-sectional view showing a third modified example of the groove in the first embodiment. FIG. 11 is a cross-sectional view showing a fourth modified example of the groove in the first embodiment. FIG. 4 is an enlarged cross-sectional view of a main portion of an eddy current reduction gear according to a second embodiment of the present invention. FIG. 11 is a cross-sectional view showing a first modified example of a groove in the second embodiment. FIG. 11 is a cross-sectional view showing a second modified example of a groove in the second embodiment. FIG. 5 is an enlarged cross-sectional view of a main portion of an eddy current reduction gear according to a third embodiment of the present invention.

[First embodiment]
First, a first embodiment of the present invention will be described.

Figure 1 is an enlarged cross-sectional view of a main portion of an eddy current reduction gear 10 according to a first embodiment of the present invention. Arrow X indicates the radial direction of the eddy current reduction gear 10, and arrow Y indicates the axial direction of the eddy current reduction gear 10. Figure 1 shows a cross section (longitudinal cross section) of the outer peripheral portion of the eddy current reduction gear 10 cut along the axial direction.

The eddy current reduction gear device 10 according to the first embodiment is mounted as an auxiliary brake on large vehicles such as trucks and buses. This eddy current reduction gear device 10 includes a rotor 12 that is fixed to a rotating shaft such as a propeller shaft or drive shaft of the vehicle, and a stator 14 that is fixed to a non-rotating part such as the vehicle's transmission.

The rotor 12 includes a drum ring 16 and a wheel 18. The drum ring 16 is formed in an annular shape and has an inner peripheral surface 16A and an outer peripheral surface 16B. The inner peripheral surface 16A and the outer peripheral surface 16B of the drum ring 16 are each formed along the axial direction of the drum ring 16. A plurality of heat dissipation fins 20 are formed on the outer peripheral surface 16B of the drum ring 16. The plurality of heat dissipation fins 20 are arranged along the circumferential direction of the drum ring 16. The drum ring 16 is made of a ferromagnetic material, and as an example, is made of steel.

The wheel 18 is disposed on one axial side of the drum ring 16. The wheel 18 has multiple arms 22 extending radially, and the tip of each arm 22 is fixed to the drum ring 16. More specifically, the drum ring 16 is fixed to a rotating shaft such as a vehicle propeller shaft or drive shaft via the wheel 18.

The stator 14 comprises a plurality of permanent magnets 24, a yoke 26, a pair of first sliding members 28, a second sliding member 30, and a casing 32. The plurality of permanent magnets 24 are disposed radially inside the drum ring 16 and are arranged along the circumferential direction of the drum ring 16. The plurality of permanent magnets 24 are arranged at equal angular intervals. The north and south poles of the plurality of permanent magnets 24 are arranged alternately in the circumferential direction of the drum ring 16.

The yoke 26 is formed in an annular shape along the circumferential direction of the drum ring 16. The yoke 26 is arranged concentrically with the drum ring 16. A number of permanent magnets 24 are fixed to the outer peripheral surface of the yoke 26. The yoke 26 is made of a ferromagnetic material.

The casing 32 has a casing cover 36 and a casing body 38. The casing cover 36 and the casing body 38 are each formed in an annular shape along the circumferential direction of the drum ring 16. The casing cover 36 has an outer cylinder portion 40 and a first connecting portion 42, and the casing body 38 has an inner cylinder portion 44 and a second connecting portion 46. The inner cylinder portion 44 and the outer cylinder portion 40 are arranged concentrically with the drum ring 16 and the yoke 26. The casing 32 is formed from a non-magnetic material.

The inner cylinder portion 44 is located radially inside the outer cylinder portion 40, and the outer cylinder portion 40 and the inner cylinder portion 44 are connected by a first connecting portion 42 and a second connecting portion 46 that extend along the radial direction of the casing 32. The above-mentioned yoke 26 and multiple permanent magnets 24 are housed between the inner cylinder portion 44 and the outer cylinder portion 40.

The pair of first sliding members 28 are slide plates, one of which is interposed between the yoke 26 and the first connecting portion 42, and the other of which is interposed between the yoke 26 and the second connecting portion 46. The second sliding member 30 is a dry bush, and is interposed between the yoke 26 and the inner cylinder portion 44. The pair of first sliding members 28 and second sliding members 30 are formed in an annular shape along the circumferential direction of the casing 32, and the yoke 26 is supported by the pair of first sliding members 28 and second sliding members 30 so as to be slidable in the circumferential direction of the casing 32.

The outer cylinder portion 40 of the casing cover 36 has a plurality of pole pieces 48. The plurality of pole pieces 48 are disposed between the drum ring 16 and the plurality of permanent magnets 24, and are arranged along the circumferential direction of the drum ring 16. The plurality of pole pieces 48 are formed of a ferromagnetic material, and are integrated with the outer cylinder portion 40 of the casing cover 36 by casting. The plurality of pole pieces 48 are the same in number as the plurality of permanent magnets 24, and are disposed at equal angular intervals, similar to the plurality of permanent magnets 24.

The outer peripheral surface of the outer tube portion 40 of the casing cover 36 is the outer peripheral surface 36A of the casing cover 36. This outer peripheral surface 36A of the casing cover 36 is formed along the axial direction of the drum ring 16 and faces the inner peripheral surface 16A of the drum ring 16. The outer peripheral surface 36A of the casing cover 36 is formed by the outer surfaces of the multiple pole pieces 48 and the outer surface of the material formed by casting between the multiple pole pieces 48.

Figure 2 is a diagram explaining how the eddy current reduction gear 10 shown in Figure 1 can be switched between a non-braked state and a braked state. In Figure 2, only the drum ring 16, permanent magnet 24, yoke 26, and pole piece 48 are shown in a cross section taken along the radial direction of the outer periphery of the eddy current reduction gear 10. Figure 2(A) shows the non-braked state of the eddy current reduction gear 10, and Figure 2(B) shows the braked state of the eddy current reduction gear 10.

The yoke 26 is rotated by an actuator (not shown), such as an air cylinder, and the circumferential positions of the multiple permanent magnets 24 fixed to the yoke 26 are changed as the yoke 26 rotates. The rotation angle of the yoke 26 corresponds to about half the arrangement angle θ of the adjacent permanent magnets 24.

As shown in FIG. 2(A), when the circumferential arrangement positions of the multiple permanent magnets 24 are switched by an actuator and adjacent permanent magnets 24 are arranged to straddle the pole piece 48, magnetic flux M passes between adjacent permanent magnets 24 and the pole piece 48. In this state, a magnetic circuit is formed between adjacent permanent magnets 24 and the pole piece 48, but a magnetic circuit is not formed between adjacent permanent magnets 24 and the drum ring 16, so no magnetic force acts on the drum ring 16. In this state, the eddy current reduction gear 10 is in a non-braking state and no braking force is generated.

On the other hand, as shown in FIG. 2(B), when the circumferential arrangement positions of the multiple permanent magnets 24 are switched by an actuator and each permanent magnet 24 is arranged to face the pole piece 48, the magnetic flux M between adjacent permanent magnets 24 reaches the drum ring 16 through the pole piece 48. In this state, a magnetic circuit is formed between adjacent permanent magnets 24 and the drum ring 16, so that a magnetic force acts on the drum ring 16. When the magnetic force acts on the drum ring 16 in this way, an eddy current is generated in the drum ring 16, and the interaction between this eddy current and the magnetic force causes a force (Lorentz force) to act on the drum ring 16 in the opposite direction to the rotation direction. In this state, the eddy current reduction gear 10 is in a braking state and a braking force is generated.

When the eddy current reduction gear 10 is in a braking state and eddy currents are generated in the drum ring 16, the drum ring 16 heats up due to Joule heat. Through various tests, the inventors have found that when the drum ring 16 heats up due to Joule heat, heat is concentrated in the axial center of the inner circumferential surface 16A of the drum ring 16 shown in Figure 1, and that this axial center becomes the highest temperature.

The inventors also discovered that if the braking state of the eddy current reduction gear 10 continues and the drum ring 16 continues to generate heat, the temperature of the axial center of the inner circumferential surface 16A of the drum ring 16 will exceed the heat-resistant temperature (e.g., about 650°C), and an oxide film (e.g., an oxide film with a thickness of about 0.5 mm) will be generated in this axial center by high-temperature oxidation, and this oxide film may come into contact with the outer circumferential surface 36A of the casing cover 36. The inventors then considered that in order to suppress the generation of an oxide film due to high-temperature oxidation, it would be effective to suppress the rate of temperature rise in the axial center of the inner circumferential surface 16A of the drum ring 16.

The inventors considered widening the gap between the inner circumferential surface 16A of the drum ring 16 and the outer circumferential surface 36A of the casing cover 36 in order to suppress the rate of temperature rise in the axial center of the inner circumferential surface 16A of the drum ring 16. However, they came to the conclusion that doing so would reduce the magnetic flux reaching the drum ring 16, thereby reducing the braking torque of the eddy current reduction gear device 10. The inventors then considered that there was room for improvement in order to extend the braking time by suppressing the rate of temperature rise in the axial center of the inner circumferential surface 16A of the drum ring 16 while maintaining the braking torque.

The inventors therefore conducted extensive research based on the above findings. As a result, they came up with the following characteristic configuration. The following describes the characteristic configuration devised by the inventors.

As shown in FIG. 1, a groove 52 is formed in the axial center of the inner peripheral surface 16A of the drum ring 16, forming an annular shape along the circumferential direction of the drum ring 16. The groove 52 is an example of a "first groove" and is formed, for example, by additional processing such as cutting. The groove 52 is formed to a depth sufficient to reduce the magnetic flux that reaches the axial center of the inner peripheral surface 16A of the drum ring 16 during braking. The depth of the groove 52 is, for example, about 0.15 mm to about 0.5 mm.

The axial center portion of the inner peripheral surface 16A of the drum ring 16 is the central portion of the inner peripheral surface 16A of the drum ring 16 in the axial direction (width direction). The groove width of the groove 52 along the axial direction of the drum ring 16 is set within a range that can suppress the generation of an oxide film due to high-temperature oxidation in the axial center portion of the inner peripheral surface 16A of the drum ring 16.

The groove 52 has a bottom surface 52A and a pair of side surfaces 52B. The bottom surface 52A is formed along the axial direction of the drum ring 16 and faces the outer peripheral surface 36A of the casing cover 36. As an example, the pair of side surfaces 52B are formed in a tapered shape in which the distance between them increases toward the casing cover 36 side. In other words, the groove 52 is formed in a tapered shape in which the groove width increases toward the casing cover 36 side. By forming the groove 52 in a tapered shape in this way, the cross-sectional shapes of the corner 52C on the opening side of the groove 52 and the corner 52D on the bottom surface 52A side of the groove 52 are both formed at obtuse angles.

The groove 52 is located within the range R of the length of the pole piece 48 along the axial direction of the drum ring 16, and opposing surfaces 54 that face the outer peripheral surface 36A of the casing cover 36 are formed on both sides of the groove 52 on the inner peripheral surface 16A of the drum ring 16. Each opposing surface 54 includes an area 54A that is located within the range R of the length of the pole piece 48.

Figure 3 is a further enlarged view of a portion of the enlarged cross section of the essential parts of the eddy current reduction gear device 10 shown in Figure 1. As described above, a groove 52 is provided in the axial center of the inner peripheral surface 16A of the drum ring 16. The groove 52 is formed into a roughly trapezoidal shape by a bottom surface 52A and a pair of side surfaces 52B when viewed in vertical cross section of the eddy current reduction gear device 10.

In a longitudinal cross-sectional view of the eddy current reduction gear 10, the bottom surface 52A is substantially parallel to the outer peripheral surface 36A of the casing cover 36. The radial distance between the bottom surface 52A and the outer peripheral surface 36A of the casing cover 36 is substantially constant over the entire circumference of the inner peripheral surface 16A of the drum ring 16. The groove 52 has a substantially constant depth D within the range of the bottom surface 52A. The depth D is, for example, 0.15 mm or more, and preferably 0.2 mm or more. It is preferable that the depth D is 0.5 mm or less.

Each of the side surfaces 52B is inclined with respect to the bottom surface 52A in a vertical cross-sectional view of the eddy current reduction gear 10. As each of the side surfaces 52B moves away from the bottom surface 52A, it approaches the outer peripheral surface 36A of the casing cover 36. Due to these side surfaces 52B, the depth of the groove 52 decreases from both ends of the bottom surface 52A toward the outside in the axial direction of the drum ring 16.

The length (groove width) _W52 of the groove 52 in the axial direction can be determined in relation to the length (magnet width) _W24 of the permanent magnet 24 in the axial direction. The groove width _W52 is preferably 0.35 times or more the magnet width _W24 . The groove width _W52 is, for example, 0.80 times or less the magnet width _W24 . The range of the length of the permanent magnet 24 along the axial direction is approximately equal to the range R ( FIG. 1 ) of the length of the pole piece 48 along the axial direction. The groove 52 is included within the range of the length of the permanent magnet 24 along the axial direction.

The axial length (bottom width) W52A of the bottom surface 52A of the groove 52 can also be determined in relation to the magnet width _W24 . _{The bottom width W52A of} the groove 52 is preferably 0.2 times or more the magnet width _W24 . The bottom width _W52A can be, for example, 0.7 times or less the magnet width _W24 .

In the groove 52, the angle of each side surface 52B with respect to the bottom surface 52A is determined in relation to the depth D, the groove width W ₅₂ , and the bottom width W _52A . The angle of each side surface 52B with respect to the bottom surface 52A is greater than 90°, and can be, for example, 170° to 179°.

Next, the operation and effects of the first embodiment will be explained.

In the eddy current reduction gear device 10 according to the first embodiment, a groove 52 is formed in the axial center of the inner peripheral surface 16A of the drum ring 16, forming an annular shape along the circumferential direction of the drum ring 16. This groove 52 therefore widens the gap (air gap) between the axial center of the inner peripheral surface 16A of the drum ring 16 and the axial center of the outer peripheral surface 36A of the casing cover 36, reducing the magnetic flux M that reaches the axial center of the inner peripheral surface 16A of the drum ring 16.

As a result, on the inner circumferential surface 16A of the drum ring 16, the magnetic flux M is dispersed on both sides of the axial center, suppressing the amount of heat generated by eddy currents in this axial center. As a result, the rate of temperature rise in the axial center of the inner circumferential surface 16A of the drum ring 16 is suppressed (i.e., localized temperature rise is mitigated), so the time it takes for the temperature in this axial center to reach the heat-resistant temperature can be extended, and thus the braking time can be extended.

Moreover, the groove 52 is formed only in the axial center, which is a part of the inner peripheral surface 16A of the drum ring 16. Therefore, the reduction in the magnetic flux M reaching the drum ring 16 can be minimized compared to, for example, moving the position of the inner peripheral surface 16A of the drum ring 16 back to the position of the bottom surface 52A of the groove 52 to increase the gap between the inner peripheral surface 16A of the drum ring 16 and the outer peripheral surface 36A of the casing cover 36. This ensures that the magnetic force acting on the drum ring 16 is secured, and therefore that braking torque is secured.

Furthermore, opposing surfaces 54 that face the outer peripheral surface 36A of the casing cover 36 are formed on both sides of the groove 52 on the inner peripheral surface 16A of the drum ring 16. Each opposing surface 54 includes an area 54A that is located within a range R of the length of the pole piece 48 along the axial direction of the drum ring 16. Therefore, magnetic flux M can pass between the pole piece 48 and the drum ring 16 through the opposing surface 54 that is located closer to the pole piece 48 than the groove 52. This ensures a magnetic force acting on the drum ring 16, and therefore a braking torque.

The groove 52 is tapered so that the groove width increases toward the casing cover 36. Therefore, the cross-sectional shapes of the corner 52C on the opening side of the groove 52 and the corner 52D on the bottom surface 52A side of the groove 52 are both formed with obtuse angles. This prevents thermal stress from concentrating on the corners 52C and 52D, and therefore prevents thermal fatigue cracks from occurring in the corners 52C and 52D due to thermal cycles.

In addition, to suppress the rate of temperature rise in the axial center portion of the inner circumferential surface 16A of the drum ring 16, it is sufficient to form a groove 52 in this axial center portion, and there is no need to change the material of the drum ring 16, which suppresses cost increases.

In addition, by suppressing the rate of temperature rise in the axial center of the inner circumferential surface 16A of the drum ring 16, radial expansion due to thermoplastic deformation of the drum ring 16 can be suppressed. This makes it possible to suppress the expansion of the gap between the inner circumferential surface 16A of the drum ring 16 and the outer circumferential surface 36A of the casing cover 36, thereby suppressing a decrease in braking torque.

Here, FIG. 4 is a graph showing test data illustrating the effectiveness of the groove 52 shown in FIG. 1. FIG. 4(A) is a graph of test data when the groove 52 is not present, and FIG. 4(B) is a graph of test data when the groove 52 is present.

In each graph, line graph G1 shows the temperature of the portion of the inner surface 16A of the drum ring 16 opposite the arm 22, line graph G2 shows the temperature of the axial center portion of the inner surface 16A of the drum ring 16, line graph G3 shows the temperature of the portion of the inner surface 16A of the drum ring 16 on the arm 22 side, and line graph G4 shows the braking torque acting on the drum ring 16.

In each graph, temperature T1 is the temperature (approximately 650°C) of the axial center of the inner surface 16A of the drum ring 16 when the heat resistance temperature is reached, and temperature T2 is the average temperature of the part of the inner surface 16A of the drum ring 16 opposite the arm 22 and the part of the inner surface 16A of the drum ring 16 on the arm 22 side. Temperature difference ΔT is the difference between temperature T1 and temperature T2.

As shown in Figures 4(A) and (B), when the groove 52 is present, the temperature difference ΔT is smaller than when the groove 52 is not present. Also, when the groove 52 is present, the time from the start of braking until the temperature of the axial center of the inner surface 16A of the drum ring 16 reaches the heat-resistant temperature (approximately 650°C) is almost doubled compared to when the groove 52 is not present.

As such, from the test data shown in Figure 4, it can be seen that when groove 52 is present, the rate of temperature rise in the axial center of the inner surface 16A of the drum ring 16 is suppressed (i.e., localized temperature rise is mitigated), so the time it takes for the temperature in this axial center to reach the heat resistance temperature can be extended, and ultimately the braking time can be extended.

In particular, in the first embodiment, the groove 52 is formed in a roughly trapezoidal shape in a vertical cross-sectional view of the eddy current reduction gear 10. That is, the groove 52 is defined by a bottom surface 52A that ensures a certain depth D, and a pair of side surfaces 52B that are inclined relative to the bottom surface 52A. In this case, the rate of temperature rise in the axial center of the inner circumferential surface 16A of the drum ring 16 can be more effectively suppressed while ensuring braking torque.

Figure 5 is a graph showing test data that explains the effectiveness of the roughly trapezoidal groove 52. Figure 5 shows the relationship between the distance from the axial center (width center) of the drum ring 16 and the heat density of the inner peripheral surface 16A of the drum ring 16 for each eddy current type reduction gear device according to the first embodiment, the conventional example, and the reference example.

In the legend of the graph in FIG. 5, "Conventional Example" indicates test data of an eddy current reduction gear without a groove 52 on the inner peripheral surface 16A of the drum ring 16. "Reference Example" indicates test data of an eddy current reduction gear having a groove with a different configuration from that of the eddy current reduction gear 10 according to the first embodiment. With reference to FIG. 6, in the eddy current reduction gear according to the reference example, a groove 52 having an arc shape in a vertical cross section is provided on the inner peripheral surface 16A of the drum ring 16. In the eddy current reduction gear according to the reference example, the maximum depth D of the groove 52 is 0.1 mm, and the length (groove width) _W52 of the groove 52 in the axial direction is approximately equal to the length (magnet width) _W24 of the permanent magnet 24 in the axial direction. On the other hand, in the eddy current reduction gear 10 according to the first embodiment, the maximum depth of the groove 52, i.e., the depth D in the range of the bottom surface 52A, is 0.2 mm, and the bottom width _W52A of the groove 52 is 0.31 times the magnet width _W24 .

As shown in FIG. 5, in the reference example and the first embodiment, the heat generation density of the inner circumferential surface 16A of the drum ring 16 is lower than in the conventional example. In particular, in the first embodiment, the maximum depth D of the groove 52 is greater than in the reference example, so the heat generation density is lower in the axial center portion of the inner circumferential surface 16A of the drum ring 16 than in the reference example. That is, in the first embodiment, the effect of suppressing the rate of temperature rise in the axial center portion of the inner circumferential surface 16A of the drum ring 16 is greater than in the reference example.

On the other hand, in the first embodiment, the heat generation density is equivalent to that of the reference example at the side 52B of the roughly trapezoidal groove 52. This is because in the first embodiment, eddy currents concentrate at the corners 52C and 52D of the groove 52, causing the current density to increase at the side 52B. From this result, it can be said that when the pair of side surfaces 52B are tapered so that the distance between the side surfaces 52B increases toward the opening side of the groove 52, the decrease in braking torque can be suppressed even if the maximum depth D of the groove 52 is relatively large. In fact, the braking torque (ratio to the braking torque of the conventional example) when the rotation speed of the rotating shaft is 3000 rpm is 0.978 in the first embodiment and 0.980 in the reference example, and the decrease rate of the braking torque is equivalent in both cases.

In this way, by forming the groove 52 with a bottom surface 52A having a constant depth D and a tapered side surface 52B, the rate of temperature rise in the axial center portion of the inner surface 16A of the drum ring 16 can be more effectively suppressed while maintaining braking torque.

Next, we will explain a variation of the first embodiment.

(First Modification)
Fig. 7 is a cross-sectional view showing a first modification of the groove 52 in the first embodiment. In the first embodiment (see Fig. 1), the cross-sectional shapes of the corner 52C on the opening side of the groove 52 and the corner 52D on the bottom surface 52A side of the groove 52 are both angular, but as shown in Fig. 7, they may both be rounded.

In this way, when the cross-sectional shapes of the corner 52C on the opening side of the groove 52 and the corner 52D on the bottom surface 52A side of the groove 52 are both rounded, the effect of suppressing the concentration of thermal stress at the corners 52C and 52D can be improved. This makes it possible to more effectively suppress the occurrence of thermal fatigue cracks due to thermal cycles at the corners 52C and 52D.

(Second Modification)
Fig. 8 is a cross-sectional view showing a second modification of the groove 52 in the first embodiment. In the first embodiment (see Fig. 1), the groove 52 has a cross-sectional shape having a bottom surface 52A and a pair of side surfaces 52B, but as shown in Fig. 8, the groove 52 may be formed in a V-shaped cross section, as an example of a tapered shape in which the groove width increases toward the casing cover 36 side.

Even with this configuration, the cross-sectional shape of the corner 52C on the opening side of the groove 52 is formed to be an obtuse angle. This prevents thermal stress from concentrating on the corner 52C, thereby preventing thermal fatigue cracks from occurring at the corner 52C due to thermal cycles. However, from the perspective of more effectively suppressing the rate of temperature rise of the inner circumferential surface 16A of the drum ring 16, it is preferable that the groove 52 has a roughly trapezoidal cross section, as shown in Figures 1, 3, and 7. The cross-sectional shape of the groove 52 may be other than the above.

(Third Modification)
FIG. 9 is a cross-sectional view showing a third modified example of the groove 52 in the first embodiment. In FIG. 9, the imaginary line L indicates the position of the inner peripheral surface of the conventional drum ring (the position of the inner peripheral surface 16A when the groove 52 in FIG. 1 is not formed). In the third modified example shown in FIG. 9, the position of the facing surface 54 is set closer to the casing cover 36 than the inner peripheral surface of the conventional drum ring, and the position of the bottom surface 52A of the groove 52 is set on the opposite side of the casing cover 36 than the inner peripheral surface of the conventional drum ring. The gap (air gap) between the facing surface 54 and the outer peripheral surface 36A of the casing cover 36 can be, for example, 0.6 mm to 0.95 mm. On the other hand, the gap (air gap) between the inner peripheral surface of the conventional drum ring and the outer peripheral surface of the casing cover is about 1.0 mm.

When configured in this manner, magnetic flux can pass between the pole piece 48 and the drum ring 16 through the opposing surface 54, which is located closer to the pole piece 48 than the inner surface of a conventional drum ring. This makes it possible to obtain a braking torque equivalent to that of a conventional drum ring, or to increase the magnetic force acting on the drum ring 16 compared to a conventional drum ring, thereby improving the braking torque.

In addition, the grooves 52 make the gap (air gap) between the axial center of the inner circumferential surface 16A of the drum ring 16 and the axial center of the outer circumferential surface 36A of the casing cover 36 larger than the inner circumferential surface of a conventional drum ring, so the magnetic flux reaching the axial center of the inner circumferential surface 16A of the drum ring 16 is reduced. This makes it possible to suppress the rate of temperature rise in the axial center of the inner circumferential surface 16A of the drum ring 16 (i.e., to mitigate localized temperature rise) compared to a conventional drum ring.

(Fourth Modification)
Fig. 10 is a cross-sectional view showing a fourth modified example of the groove 52 in the first embodiment. In the first embodiment (see Fig. 1), one groove 52 is formed in the axial center of the inner circumferential surface 16A of the drum ring 16. However, as shown in Fig. 10, a plurality of grooves 52 may be formed in the axial center of the inner circumferential surface 16A of the drum ring 16 aligned in the axial direction of the drum ring 16.

When configured in this manner, opposing surfaces 56 that face the pole piece 48 are formed between the multiple grooves 52, and magnetic flux can pass between the pole piece 48 and the drum ring 16 through these opposing surfaces 56. This suppresses the rate of temperature rise in the axial center of the inner circumferential surface 16A of the drum ring 16, while increasing the magnetic force acting on the drum ring 16 compared to, for example, a case in which a single groove 52 is formed in the axial center of the inner circumferential surface 16A of the drum ring 16, thereby improving the braking torque.

[Second embodiment]
Next, a second embodiment of the present invention will be described.

Figure 11 is an enlarged cross-sectional view of a main portion of an eddy current reduction gear 60 according to a second embodiment of the present invention. The eddy current reduction gear 60 according to the second embodiment is modified in configuration as follows from the eddy current reduction gear 10 according to the first embodiment described above (see Figure 1).

That is, in the eddy current reduction gear 60 according to the second embodiment, a groove 62 is formed in the axial center of the outer circumferential surface 36A of the casing cover 36, forming an annular shape along the circumferential direction of the casing cover 36. The groove 62 is an example of a "second groove" and is formed, for example, by additional processing such as cutting.

The groove 62 is formed to a depth sufficient to reduce the magnetic flux reaching the axial center of the inner circumferential surface 16A of the drum ring 16 when braking. The groove 62 is also formed to a depth sufficient to prevent magnetic leakage to the drum ring 16 side when not braking due to the thinning of the pole piece 48. The depth of the groove 62 is, for example, about 0.15 mm to about 0.5 mm. The groove width of the groove 62 along the axial direction of the drum ring 16 is set to a range sufficient to suppress the generation of an oxide film due to high-temperature oxidation in the axial center of the inner circumferential surface 16A of the drum ring 16.

The groove 62 has a cross-sectional shape (roughly trapezoidal) similar to that of the groove 52 of the first embodiment (see FIG. 1), and has a bottom surface 62A and a pair of side surfaces 62B. The bottom surface 62A is formed along the axial direction of the casing cover 36 and faces the inner peripheral surface 16A of the drum ring 16. As an example, the pair of side surfaces 62B are formed in a tapered shape in which the distance between them increases toward the drum ring 16 side. In other words, the groove 62 is formed in a tapered shape in which the groove width increases toward the drum ring 16 side.

The groove 62 has a substantially constant depth within the range of the bottom surface 62A, similar to the groove 52 of the first embodiment. The depth of the groove 62 within the range of the bottom surface 62A is, for example, 0.15 mm to 0.5 mm, and preferably 0.2 mm to 0.5 mm. The length of the groove 62 in the axial direction and the length of the bottom surface 62A can be set in the same manner as the groove 52 of the first embodiment in relation to the length of the permanent magnet 24 in the axial direction. The angle of each side surface 62B relative to the bottom surface 62A can also be set in the same manner as the groove 52 of the first embodiment.

The groove 62 is located within the range R of the length of the pole piece 48 along the axial direction of the casing cover 36, and opposing surfaces 64 that face the inner peripheral surface 16A of the drum ring 16 are formed on both sides of the groove 62 on the outer peripheral surface 36A of the casing cover 36. Each opposing surface 64 includes an area 64A that is located within the range R of the length of the pole piece 48.

In the eddy current reduction gear 60 according to the second embodiment, no groove 52 (see FIG. 1) is formed in the axial center of the inner circumferential surface 16A of the drum ring 16, and the inner circumferential surface 16A of the drum ring 16 is formed flat along the axial direction of the drum ring 16.

Next, the operation and effects of the second embodiment will be explained.

In the eddy current reduction gear 60 according to the second embodiment, a groove 62 is formed in the axial center of the outer peripheral surface 36A of the casing cover 36, forming an annular shape along the circumferential direction of the casing cover 36. This groove 62 therefore widens the gap (air gap) between the axial center of the inner peripheral surface 16A of the drum ring 16 and the axial center of the outer peripheral surface 36A of the casing cover 36, reducing the magnetic flux M that reaches the axial center of the inner peripheral surface 16A of the drum ring 16.

As a result, on the inner circumferential surface 16A of the drum ring 16, the magnetic flux M is dispersed on both sides of the axial center, suppressing the amount of heat generated by eddy currents in this axial center. As a result, the rate of temperature rise in the axial center of the inner circumferential surface 16A of the drum ring 16 is suppressed (i.e., localized temperature rise is mitigated), so the time it takes for the temperature in this axial center to reach the heat-resistant temperature can be extended, and thus the braking time can be extended.

Moreover, the groove 62 is formed only in the axial center, which is a part of the outer peripheral surface 36A of the casing cover 36. Therefore, the reduction in the magnetic flux M reaching the drum ring 16 can be minimized, compared to, for example, the case where the position of the outer peripheral surface 36A of the casing cover 36 is set back to the position of the bottom surface 62A of the groove 62 to increase the gap between the inner peripheral surface 16A of the drum ring 16 and the outer peripheral surface 36A of the casing cover 36. This ensures that the magnetic force acting on the drum ring 16 is secured, and therefore the braking torque is secured.

Furthermore, on both sides of the groove 62 on the outer peripheral surface 36A of the casing cover 36, opposing surfaces 64 that face the inner peripheral surface 16A of the drum ring 16 are formed. Each opposing surface 64 includes an area 64A located within a range R of the length of the pole piece 48 along the axial direction of the drum ring 16. Therefore, magnetic flux M can pass between the pole piece 48 and the drum ring 16 through the opposing surface 64 located closer to the drum ring 16 than the groove 62. This ensures a magnetic force acting on the drum ring 16, and therefore a braking torque.

In addition, to suppress the rate of temperature rise at the axial center of the inner circumferential surface 16A of the drum ring 16, it is sufficient to form a groove 62 at the axial center of the outer circumferential surface 36A of the casing cover 36, and there is no need to change the material of the drum ring 16, which suppresses cost increases.

In addition, by suppressing the rate of temperature rise in the axial center of the inner circumferential surface 16A of the drum ring 16, radial expansion due to thermoplastic deformation of the drum ring 16 can be suppressed. This makes it possible to suppress the expansion of the gap between the inner circumferential surface 16A of the drum ring 16 and the outer circumferential surface 36A of the casing cover 36, thereby suppressing a decrease in braking torque.

In the first embodiment (see FIG. 1), a groove 52 is formed in the axial center of the inner circumferential surface 16A of the drum ring 16, so the distance between this axial center and the permanent magnet 24 is longer. In contrast, in the second embodiment, a groove 62 is formed in the axial center of the outer circumferential surface 36A of the casing cover 36, so the distance between the drum ring 16 and the permanent magnet 24 remains unchanged. Therefore, the magnetic resistance between the drum ring 16 and the permanent magnet 24 can be reduced compared to the first embodiment.

In the first embodiment (see FIG. 1), the groove 52 is formed in the axial center of the inner peripheral surface 16A of the drum ring 16, which is a heating body and a rotating body, and there is a concern that thermal stress will concentrate at the corner 52C on the opening side of the groove 52 and the corner 52D on the bottom surface 52A side of the groove 52. In contrast, in the second embodiment, the groove 62 is formed in the axial center of the outer peripheral surface 36A of the casing cover 36, which is a non-heating body and a non-rotating body, and it is possible to avoid thermal stress concentration at the corner 62C on the opening side of the groove 62 and the corner 62D on the bottom surface 62A side of the groove 62. This makes it possible to suppress the occurrence of thermal fatigue cracks due to thermal cycles in the corners 62C and 62D, and therefore increases the degree of freedom in machining the groove 62.

Next, we will explain a modified example of the second embodiment.

(First Modification)
Fig. 12 is a cross-sectional view showing a first modification of the groove 62 in the second embodiment. In the second embodiment (see Fig. 11), the groove 62 is formed in a tapered shape in which the groove width increases toward the drum ring 16 side, but as shown in Fig. 12, the groove 62 may be formed in a rectangular cross section in which the groove width is constant throughout the depth direction.

(Second Modification)
Fig. 13 is a cross-sectional view showing a second modified example of the groove 62 in the second embodiment. In the second embodiment (see Fig. 11), one groove 62 is formed in the axial center of the outer circumferential surface 36A of the casing cover 36, but as shown in Fig. 13, a plurality of grooves 62 may be formed in the axial center of the outer circumferential surface 36A of the casing cover 36 aligned in the axial direction of the casing cover 36.

When configured in this manner, opposing surfaces 66 that face the drum ring 16 are formed between the multiple grooves 62, and magnetic flux can pass between the pole piece 48 and the drum ring 16 through these opposing surfaces 66. This suppresses the rate of temperature rise in the axial center of the inner circumferential surface 16A of the drum ring 16, while increasing the magnetic force acting on the drum ring 16 compared to, for example, a case in which a single groove 62 is formed in the axial center of the outer circumferential surface 36A of the casing cover 36, thereby improving the braking torque.

(Other Modifications)
In the second embodiment, the groove 62 has, as an example, the same depth and groove width as the groove 52 (see FIG. 1) in the first embodiment, but at least one of the depth and groove width may be different.

[Third embodiment]
Next, a third embodiment of the present invention will be described.

Figure 14 is an enlarged cross-sectional view of a main portion of an eddy current reduction gear 70 according to a third embodiment of the present invention. The eddy current reduction gear 70 according to the third embodiment is modified in configuration as follows from the eddy current reduction gear 10 according to the first embodiment (see Figure 1) and the eddy current reduction gear 60 according to the second embodiment (see Figure 11) described above.

That is, in the eddy current reduction gear 70 according to the third embodiment, a groove 52 is formed in the axial center of the inner peripheral surface 16A of the drum ring 16, and a groove 62 is formed in the axial center of the outer peripheral surface 36A of the casing cover 36. Groove 52 is an example of a "first groove," and groove 62 is an example of a "second groove." Groove 52 is similar to groove 52 of the first embodiment (see FIG. 1), and groove 62 is similar to groove 62 of the second embodiment (see FIG. 11).

Next, the operation and effects of the third embodiment will be explained.

In the eddy current reduction gear 70 according to the third embodiment, a groove 52 is formed in the axial center of the inner peripheral surface 16A of the drum ring 16, forming an annular shape along the circumferential direction of the drum ring 16, and a groove 62 is formed in the axial center of the outer peripheral surface 36A of the casing cover 36, forming an annular shape along the circumferential direction of the casing cover 36. Therefore, these grooves 52, 62 increase the distance (air gap) between the axial center of the inner peripheral surface 16A of the drum ring 16 and the axial center of the outer peripheral surface 36A of the casing cover 36, and the magnetic flux M reaching the axial center of the inner peripheral surface 16A of the drum ring 16 decreases.

As a result, on the inner circumferential surface 16A of the drum ring 16, the magnetic flux M is dispersed on both sides of the axial center, suppressing the amount of heat generated by eddy currents in this axial center. As a result, the rate of temperature rise in the axial center of the inner circumferential surface 16A of the drum ring 16 is suppressed (i.e., localized temperature rise is mitigated), so the time it takes for the temperature in this axial center to reach the heat-resistant temperature can be extended, and thus the braking time can be extended.

Moreover, the groove 52 is formed only in the axial center, which is a part of the inner peripheral surface 16A of the drum ring 16, and the groove 62 is formed only in the axial center, which is a part of the outer peripheral surface 36A of the casing cover 36. Therefore, the reduction in the magnetic flux M reaching the drum ring 16 can be minimized compared to, for example, the case where the position of the inner peripheral surface 16A of the drum ring 16 and the position of the outer peripheral surface 36A of the casing cover 36 are moved back to the positions of the bottom surfaces 52A, 62A of the grooves 52, 62, respectively, to widen the gap between the inner peripheral surface 16A of the drum ring 16 and the outer peripheral surface 36A of the casing cover 36. This ensures the magnetic force acting on the drum ring 16, and therefore the braking torque.

In addition, on both sides of the groove 52 on the inner peripheral surface 16A of the drum ring 16, opposing surfaces 54 that face the outer peripheral surface 36A of the casing cover 36 are formed. Each opposing surface 54 includes an area 54A located within the range R of the length of the pole piece 48 along the axial direction of the drum ring 16. Similarly, on both sides of the groove 62 on the outer peripheral surface 36A of the casing cover 36, opposing surfaces 64 that face the inner peripheral surface 16A of the drum ring 16 are formed. Each opposing surface 64 includes an area 64A located within the range R of the length of the pole piece 48 along the axial direction of the drum ring 16. Therefore, magnetic flux M can pass between the pole piece 48 and the drum ring 16 through the opposing surfaces 54, 64, which are closer to each other than the grooves 52, 62. This ensures a magnetic force acting on the drum ring 16, and therefore a braking torque.

Next, we will explain a modified example of the third embodiment.

In the third embodiment, the groove 52 formed in the axial center of the inner circumferential surface 16A of the drum ring 16 may be modified in the first to fourth manners described above according to the first embodiment. Also, in the third embodiment, the groove 62 formed in the axial center of the outer circumferential surface 36A of the casing cover 36 may be modified in the first and second manners described above according to the second embodiment.

In the third embodiment, the grooves 52 and 62 have the same depth and groove width, for example, but at least one of the depth and groove width may be different.

The above describes the first to third embodiments of the present invention, but the present invention is not limited to the above, and can of course be modified in various ways without departing from the spirit of the invention.

First Embodiment
10 Eddy current type reduction gear 12 Rotor 14 Stator 16 Drum ring 16A Inner peripheral surface 24 Permanent magnet 36 Casing cover 36A Outer peripheral surface 48 Pole piece 52 Groove (an example of a first groove)
52A Bottom surface 52B Side surface 54 Opposing surface (Second embodiment)
60 Eddy current type reduction gear 62 Groove (an example of a second groove)
64 opposing surface (third embodiment)
70 Eddy current reduction gear

Claims (5)

A circular drum ring,
A plurality of permanent magnets are disposed radially inside the drum ring and arranged along a circumferential direction of the drum ring;
a casing cover having an annular shape, the casing cover having a plurality of pole pieces arranged along a circumferential direction of the drum ring and disposed between the drum ring and the plurality of permanent magnets, the outer circumferential surface of the casing cover facing an inner circumferential surface of the drum ring;
In an eddy current reduction gear comprising:
a first groove formed in the axial center of the inner peripheral surface of the drum ring and having an annular shape along the circumferential direction of the drum ring, and a second groove formed in the axial center of the outer peripheral surface of the casing cover and having an annular shape along the circumferential direction of the casing cover ,
a length of the first groove in the axial direction of the drum ring is 0.35 times or more and 0.80 times or less the length of each of the permanent magnets in the axial direction of the drum ring;
The first groove is tapered such that the groove width increases toward the casing cover, and has a bottom surface formed along the axial direction of the drum ring and facing the outer circumferential surface of the casing cover, and a pair of side surfaces tapered such that the distance between them increases toward the casing cover,
When the eddy current reduction gear device has the first groove, opposing surfaces are formed on both sides of the first groove on the inner peripheral surface of the drum ring, the opposing surfaces including an area located within a range of the length of the pole piece along the axial direction of the drum ring, and opposing the outer peripheral surface of the casing cover,
a length of the second groove in the axial direction of the drum ring is 0.35 to 0.80 times the length of each of the permanent magnets in the axial direction of the drum ring;
The second groove is tapered such that the groove width increases toward the drum ring, and has a bottom surface formed along the axial direction of the casing cover and facing the inner peripheral surface of the drum ring, and a pair of side surfaces tapered such that the distance between them increases toward the drum ring,
When the eddy current reduction gear device has the second groove, the outer circumferential surface of the casing cover has opposing surfaces on both sides of the second groove, the opposing surfaces including an area within a length of the pole piece along the axial direction of the drum ring, the opposing surfaces facing the inner circumferential surface of the drum ring.
Eddy current reduction gear. The first groove is provided.
2. The eddy current reduction gear according to claim 1. A plurality of the first grooves are provided,
The first grooves are formed in a line in the axial direction of the drum ring.
2. The eddy current reduction gear according to claim 1 . The second groove is provided.
The eddy current reduction gear according to any one of claims 1 to 3 . A plurality of the second grooves are provided,
The second grooves are formed in a line in the axial direction of the casing cover.
The eddy current reduction gear according to any one of claims 1 to 3 .

Images