Magnetic viscous fluid device

Abstract

To provide a magnetic viscous fluid device which can be downsized while suppressing reduction of torque that is transferred between members via a magnetic viscous fluid.SOLUTION: A magnetic viscous fluid device 1 comprises: a rotary plate 20 which is fixed to a rotary shaft 10; yokes 30 and 40 having a first opposite face that is opposed to the rotary plate 20 via a first clearance and a second opposite face that is opposed to the rotary plate 20 via a second clearance; a magnetic viscous fluid 50 filling the first and second clearances; and a coil 60 forming a magnetic path at the time of electrification. A casing 80 using a non-magnetic substance is extrapolated to a part of outer peripheral surfaces of the yokes 30 and 40. The casing 80 is disposed so as to cover a part of a region, in which the coil 60 is present radially inside and not to cover the remaining part of the coil including region on the outer peripheral surface of the yoke 30. In a view in a direction of an axis, a part of the coil including region on the outer peripheral surface of the yoke 30 is formed inside while being inscribed or not being inscribed to the remaining part of the coil including region on the outer peripheral surface of the yoke 30.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a magnetorheological fluid device in which a magnetorheological fluid is interposed between components that are arranged to be rotatable relative to one another, and the torque transmitted between the components is variable by changing the strength of the magnetic field applied to the magnetorheological fluid. [Background technology]

[0002] This type of magnetorheological fluid device is disclosed, for example, in Patent Documents 1 and 2. The magnetorheological fluid device disclosed in Patent Document 1 and the rotary braking device (magnetorheological fluid device) disclosed in Patent Document 2 include a rotating plate and yokes arranged on both sides of the rotating plate, facing each other. The two yokes are connected and fixed to each other by a cylindrical casing made of a non-magnetic material.

[0003] In these magnetorheological fluid devices, a minute gap is formed between the rotating plate and the yoke, and the gap is filled with magnetorheological fluid. A magnetic field is formed between the yokes, which are arranged opposite each other on both sides of the rotating plate, penetrating the rotating plate and the magnetorheological fluid. This causes the magnetorheological fluid to develop a viscosity that corresponds to the strength of the magnetic field, and torque that corresponds to the strength of the magnetic field is transmitted between the rotating plate and the yoke. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-109155 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-181778 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been an increasing demand for compact magnetorheological fluid devices with smaller outer diameters. To reduce the outer diameter of a magnetorheological fluid device equipped with a casing made of a non-magnetic material, such as the magnetorheological fluid devices disclosed in Patent Documents 1 and 2, one possible approach is to reduce the thickness or outer diameter of the casing. However, if the casing thickness cannot be reduced to ensure the required strength, it is necessary to reduce the outer and inner diameters of the casing while maintaining the casing thickness, and also reduce the outer diameter of the yoke inside the casing.

[0006] However, if the outer diameter of the yoke is uniformly reduced, the magnetic resistance of the magnetic circuit formed within the magnetorheological fluid device increases, and when a magnetic field is applied to the magnetorheological fluid, the torque transmitted between the rotating plate and the yoke via the magnetorheological fluid decreases.

[0007] The present invention was devised in light of these problems, and aims to provide a magnetorheological fluid device that can be miniaturized while suppressing a decrease in the torque transmitted between components (for example, between a rotating plate and a yoke) via a magnetorheological fluid. [Means for solving the problem]

[0008] A magnetorheological fluid device according to a first aspect of the present invention includes a rotating plate fixed to a rotating shaft that rotates about an axis; a yoke having a first opposing surface facing one main surface of the rotating plate across a first gap and a second opposing surface facing the other main surface of the rotating plate across a second gap; magnetorheological fluid filled in the first gap and the second gap; and a coil housed in the yoke and shaped to circle the axis, which forms a magnetic path passing through the yoke, the rotating plate, and the magnetorheological fluid when current is applied. The rotating plate is rotatable relative to the yoke. A casing made of a non-magnetic material is fitted onto a portion of the outer circumferential surface of the yoke. The casing is disposed so as to cover a portion of the region of the outer circumferential surface of the yoke where the coil is located radially inward (hereinafter referred to as the "coil-containing region"), but not cover the remainder of the coil-containing region. When viewed from the direction of the axis, the portion of the coil-containing region on the outer surface of the yoke is formed inside the remaining portion of the coil-containing region on the outer surface of the yoke, with or without being inscribed in the remaining portion.

[0009] A magnetorheological fluid device having such a configuration can reduce the influence of the casing, which is a non-magnetic material, on the magnetic path.

[0010] A magnetorheological fluid device according to a second aspect of the present invention is the magnetorheological fluid device according to the first aspect, wherein the yoke includes a first yoke having the first opposing surface and accommodating the coil, and a second yoke having the second opposing surface, and the casing is fitted over the portion of the coil-containing region on the outer circumferential surface of the first yoke and over at least a portion of the outer circumferential surface of the second yoke.

[0011] A third aspect of the present invention is a magnetorheological fluid device according to the second aspect, wherein the first yoke has a portion radially sandwiched between the inner surface of the casing and the outer surface of the coil, where the magnetic resistance is greatest in the magnetic circuit formed when the coil is energized.

[0012] A magnetorheological fluid device according to a fourth aspect of the present invention is the magnetorheological fluid device according to any one of the first to third aspects, in which the yoke portion is not disposed between the coil and the rotating plate.

[0013] A magnetorheological fluid device according to a fifth aspect of the present invention is the magnetorheological fluid device according to any one of the first to third aspects, wherein the yoke portion is disposed between the coil and the rotating plate. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a magnetorheological fluid device that can be made smaller while suppressing a decrease in torque transmitted between members (for example, between a rotating plate and a yoke) via a magnetorheological fluid. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view showing a magnetorheological fluid device according to a first embodiment of the present invention. [Figure 2] FIG. 3 is a cross-sectional view showing a magnetorheological fluid device according to a second embodiment of the present invention. [Figure 3] FIG. 10 is a cross-sectional view showing a magnetorheological fluid device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] A magnetorheological fluid device 1 according to a first embodiment of the present invention will be described below with reference to the drawings. In this specification, "axis N" refers to the axis N of the rotating shaft 10, "radial direction" refers to the radial direction of the rotating shaft 10, "upward" refers to one side of the axis N direction, and "downward" refers to the other side of the axis N direction. Of course, the use state of the magnetorheological fluid device 1 is not limited to a state in which the axis N of the rotating shaft 10 is oriented in the vertical direction in real space. In addition, in the drawings, the dashed line with an arrow indicated by the symbol P exemplifies a magnetic path (magnetic circuit).

[0017] First Embodiment As shown in FIG. 1, the magnetorheological fluid device 1 according to this embodiment includes a rotating shaft 10, a rotating plate 20, a first yoke 30, a second yoke 40, a magnetorheological fluid 50, a coil 60, a spacer 70, and a casing 80.

[0018] The rotating shaft 10 is supported so as to be rotatable about an axis N via a bearing 90 press-fitted into a shaft hole 31 formed in the first yoke 30. The rotating shaft 10 is formed with, in order from the top, a general portion 11, a first small diameter portion 12, a medium diameter portion 13, a second small diameter portion 14, a flange portion 15, and a tip portion 16.

[0019] The first small diameter portion 12 and the second small diameter portion 14 have a smaller diameter than the general portion 11. The flange portion 15 has a larger diameter than the general portion 11. The medium diameter portion 13 has a larger diameter than the general portion 11 and a smaller diameter than the flange portion 15. The tip portion 16 has a smaller diameter than the first small diameter portion 12 and the second small diameter portion 14, and has a shape in which the diameter becomes even smaller downward due to a step. The tip portion 16 is inserted into the through hole 23 of the rotating plate 20. The material of the rotating shaft 10 is preferably a non-magnetic material such as stainless steel.

[0020] A retaining ring 17 is attached to the general portion 11 of the rotating shaft 10, so that downward movement of the axis N is restricted relative to the bearing 90. The bearing 90 may be a plain bearing or a rolling bearing. In this embodiment, the rotating shaft 10 is rotatably supported by the bearing 90 attached to the first yoke 30, but a bearing may also be provided in the second yoke 40, and the rotating shaft 10 may be supported by this bearing.

[0021] The rotating plate 20 is, for example, a circular disk. The rotating plate 20 has a first main surface 21 located on the upper side and a second main surface 22 located on the lower side. A through hole 23 is formed in the center of the rotating plate 20. The through hole 23 has a shape in which the diameter becomes smaller at the bottom due to a step. The tip portion 16 of the rotating shaft 10 is inserted into the through hole 23, and the rotating plate 20 is fixed to the rotating shaft 10 with the tip portion 16 in contact with the lower surface of the flange portion 15. The rotating plate 20 rotates integrally with the rotating shaft 10.

[0022] In this embodiment, the first yoke 30 and the second yoke 40 function as yokes through which a magnetic path, indicated by the dashed arrowed line P and formed around the coil 60, passes. The first yoke 30 and the second yoke 40 are each made of a magnetic material. A casing 80 is fitted around the first yoke 30 and the second yoke 40, and the first yoke 30 and the second yoke 40 are fixed to each other via the casing 80.

[0023] A space for accommodating the coil 60 and a space for accommodating the bearing 90 and the rotating shaft 10 are formed within the first yoke 30. A space for rotatably accommodating the rotating plate 20 and for accommodating the magnetorheological fluid 50 is formed between the first yoke 30 and the second yoke 40. Torque is transmitted between the first yoke 30, the second yoke 40, and the rotating plate 20 via the magnetorheological fluid 50.

[0024] As shown in FIG. 1, the first yoke 30 is disposed above the rotating plate 20. The first yoke 30 has an annular groove 32 centered on the axis N for arranging the coil 60. The annular groove 32 opens downward. The radial center of the annular groove 32 coincides with the axis N. The space within the annular groove 32 serves as a space for accommodating the coil 60. In this embodiment, the first yoke 30 is formed in a substantially annular shape centered on the axis N.

[0025] The first yoke 30 has two first opposing surfaces 34a, 34b that face the first main surface 21 of the rotating plate 20 across a first gap S1. The first opposing surface 34a is located radially inward of the annular groove 32, and the first opposing surface 34b is located radially outward of the annular groove 32.

[0026] The first yoke 30 has a shaft hole 31 in the center for passing the rotating shaft 10 therethrough. A first large diameter portion 31b is formed above an intermediate portion 31a of the shaft hole 31. The first large diameter portion 31b has an inner diameter larger than that of the intermediate portion 31a. A bearing 90 is press-fitted into the first large diameter portion 31b and fixed to the first yoke 30. Furthermore, a second large diameter portion 31c is formed below the intermediate portion 31a of the shaft hole 31. The outer periphery of the flange 15 of the rotating shaft 10 is inserted into the second large diameter portion 31c. The inner diameter of the second large diameter portion 31c is set to be slightly larger than the outer diameter of the flange 15 of the rotating shaft 10.

[0027] When the rotating shaft 10 is inserted from below into the shaft hole 31, the flange 15 of the rotating shaft 10 is inserted into the second large diameter portion 31c. At this time, when the side surface of the flange 15 near the outer periphery abuts against the step between the second large diameter portion 31c and the intermediate portion 31a, the rotating shaft 10 is unable to move upward along the axis N. When the rotating shaft 10 is fixed with the retaining ring 17 so as not to move downward along the axis N relative to the bearing 90, the rotating shaft 10 is positioned in the direction of the axis N so as to be rotatable relative to the first yoke 30. Furthermore, because the rotating plate 20 is fixed to the rotating shaft 10, the rotating plate 20 is also positioned in the direction of the axis N so as to be rotatable relative to the first yoke 30.

[0028] Shaft seal members 91 are provided between the inner circumferential surface of the intermediate portion 31a of the shaft hole 31 and the first small diameter portion 12 and the second small diameter portion 14 of the rotating shaft 10. The shaft seal members 91 seal between the first yoke 30 and the rotating shaft 10 to prevent the magnetorheological fluid 50 (described later) from leaking upward. For example, an O-ring or a Y-packing is used as the shaft seal member 91. The shaft seal members 91 are arranged above and below the medium diameter portion 13 of the rotating shaft 10.

[0029] The outer peripheral surface of the first yoke 30 is provided with an annular step 33, the diameter of which is smaller at the bottom than at the top. The portion of the outer peripheral surface of the first yoke 30 below the step 33 is inserted into the casing 80 and fixed to the casing 80. The outer diameter of the first yoke 30 below the step 33 is set to be approximately equal to the inner diameter of the casing 80. The outer diameter of the first yoke 30 above the step 33 is set to be approximately equal to the outer diameter of the casing 80. The outer diameter of the first yoke 30 above the step 33 may be larger or smaller than the outer diameter of the casing 80. It is sufficient that the outer diameter of the first yoke 30 is smaller at the bottom, where the casing 80 is fitted, than at the top. Alternatively, a tapered portion whose diameter decreases from top to bottom may be provided instead of the step 33.

[0030] An annular groove 301 is provided on the outer peripheral surface of the first yoke 30 below the step 33. An O-ring 92 is inserted into the annular groove 301. The O-ring 92 seals the gap between the first yoke 30 and the casing 80.

[0031] 1, the second yoke 40 is provided so that the rotating plate 20 is interposed between the second yoke 40 and the first yoke 30. The second yoke 40 has a disk shape that extends in a direction perpendicular to the axis N and is centered on the axis N. The second yoke 40 has a second opposing surface 41 that faces the second main surface 22 of the rotating plate 20 across a second gap S2. The second opposing surface 41 is disposed at a predetermined distance from the first opposing surfaces 34a and 34b of the first yoke 30.

[0032] The second yoke 40 is fitted into a cylindrical casing 80 and fixed to the casing 80. The second yoke 40 is fixed to the first yoke 30 via the casing 80. The outer diameter of the second yoke 40 is set to be approximately equal to the outer diameter of the first yoke 30 below the step 33, and is set to be approximately equal to the inner diameter of the casing 80. An annular groove 44 is formed on the outer peripheral surface of the second yoke 40. An O-ring 92 is inserted into the annular groove 44. The O-ring 92 seals the gap between the second yoke 40 and the casing 80.

[0033] The magnetorheological fluid 50 is accommodated in a space for accommodating the magnetorheological fluid 50 within the first yoke 30 and the second yoke 40. The space for accommodating the magnetorheological fluid 50 is a space formed between the first opposing surfaces 34a, 34b of the first yoke 30 and the second opposing surface 41 of the second yoke 40, excluding the rotating plate 20. In FIG. 1 , the space for accommodating the magnetorheological fluid 50 is the area shaded gray. The magnetorheological fluid 50 is present in a first gap S1 between the rotating plate 20 and the first yoke 30 and a second gap S2 between the rotating plate 20 and the second yoke 40, and transmits torque between them according to its viscosity.

[0034] The magnetorheological fluid 50 is a liquid in which magnetic particles are dispersed in a dispersion medium, and in particular, magnetic particles made of nano-sized metal particles (metal nanoparticles) can be used. The magnetic particles are made of a magnetizable metal material, and although there are no particular restrictions on the metal material, soft magnetic materials are preferred. Examples of soft magnetic materials include alloys of iron, cobalt, nickel, and permalloy. The dispersion medium is not particularly limited, but hydrophobic silicone oil is one example. The amount of magnetic particles in the magnetorheological fluid 50 may be, for example, 3 to 40 vol%. Various additives can also be added to the magnetorheological fluid 50 to obtain various desired properties.

[0035] The coil 60 has a shape that wraps around the axis N, and is disposed in the annular groove 32 of the first yoke 30. In this embodiment, the coil 60 is formed by winding a coil conductor around a bobbin 61, and the coil 60 and the bobbin 61 are disposed in the annular groove 32. In this embodiment, the coil 60 uses the bobbin 61, but it is also possible to dispose the coil 60 in the annular groove 32 of the first yoke 30 without using the bobbin 61. Regarding the arrangement of the coil 60, in this embodiment, the coil 60 is disposed above the rotating plate 20, but it is also possible to dispose the coil 60 radially outward from the rotating plate 20.

[0036] An external current supply device supplies current to the coil 60 via a power line (not shown). The current supply device controls the value of the current supplied to the coil 60. When a current flows through the coil 60, a magnetic path is formed that passes through the first yoke 30, the magnetorheological fluid 50 present in the first gap S1, the rotating plate 20, the magnetorheological fluid 50 present in the second gap S2, and the second yoke 40 along the direction indicated by the dashed arrow line P in FIG. 1. A magnetic field corresponding to the value of the current applied to the coil 60 is then applied to the magnetorheological fluid 50 present in the first gap S1 and the second gap S2.

[0037] The spacer 70 has a ring shape. The spacer 70 is made of a non-magnetic material. The spacer 70 is interposed between the first yoke 30 and the second yoke 40 radially outward from the outer circumferential surface of the rotating plate 20, in a state of contact with the first yoke 30 and the second yoke 40. In this embodiment, the spacer 70 is interposed between the first opposing surface 34b of the first yoke 30 and the second opposing surface 41 of the second yoke 40. The outer circumferential surface of the spacer 70 is in contact with the inner circumferential surface of the casing 80.

[0038] The casing 80 is made of a non-magnetic material. In this embodiment, the entire casing 80 is made of a non-magnetic material. Examples of non-magnetic materials that can be used include resin, stainless steel, and aluminum. If the casing 80 is made of an insulating material such as resin, it is possible to prevent current leakage from the magnetorheological fluid device 1 to the outside and current flow into the magnetorheological fluid device 1 from surrounding equipment.

[0039] The casing 80 has a substantially cylindrical shape. The casing 80 is fitted over a portion of the outer circumferential surface of the first yoke 30 and the entire outer circumferential surface of the second yoke 40. The casing 80 is disposed so as to cover a portion A1 of the coil-containing region A where the coil 60 is located radially inward on the outer circumferential surface of the first yoke 30, but not cover a remaining portion A2 of the coil-containing region A. Therefore, the outer diameter of the portion of the outer circumferential surface of the first yoke 30 corresponding to the portion A1 of the coil-containing region A is smaller than the outer diameter of the portion of the outer circumferential surface of the first yoke 30 corresponding to the remaining portion A2 of the coil-containing region A. In other words, when viewed from the direction of the axis N, the portion of the outer circumferential surface of the first yoke 30 corresponding to the portion A1 of the coil-containing region A is formed inside the portion of the outer circumferential surface of the first yoke 30 corresponding to the remaining portion A2 of the coil-containing region A without being inscribed therein.

[0040] The casing 80 is not limited to a cylindrical shape, and may have various shapes, such as a rectangular tube shape, depending on the shape of the magnetorheological fluid device 1. With regard to the outer peripheral surface of the first yoke 30, a portion A1 of the outer peripheral surface of the first yoke 30 corresponding to the portion within the coil-containing region A may be formed inside and inscribed with a portion A2 of the outer peripheral surface of the first yoke 30 corresponding to the remaining portion A2 of the coil-containing region A when viewed from the direction of the axis N. For example, a circumferential portion of the portion A1 of the outer peripheral surface of the first yoke 30 corresponding to the portion within the coil-containing region A may protrude or bulge in the radial direction, or a circumferential portion of the portion A2 of the outer peripheral surface of the first yoke 30 corresponding to the remaining portion A2 of the coil-containing region A may be recessed, so that the portion A1 of the outer peripheral surface of the first yoke 30 corresponding to the portion within the coil-containing region A may be formed inside and inscribed with a portion A2 of the outer peripheral surface of the first yoke 30 corresponding to the portion within the coil-containing region A when viewed from the direction of the axis N.

[0041] In this embodiment, the height of the casing 80 is approximately half the height of the magnetorheological fluid device 1, and the entire second yoke 40 and a portion of the first yoke 30 are inserted into the casing 80. At this time, the upper end of the casing 80 abuts against the step 33. The casing 80 is then fixed to the first yoke 30 and the second yoke 40 with adhesive, bolts, or the like, thereby connecting and fixing the first yoke 30 and the second yoke 40. In this embodiment, the entire second yoke 40 is inserted into the casing 80. However, only a portion of the second yoke 40, for example, only the upper half of the second yoke 40, may be inserted into the casing 80. In this case, an annular step may be provided on the outer peripheral surface of the second yoke 40, and the outer diameter below the step may be made larger. In this way, the casing 80 does not need to be fitted over the entire outer peripheral surface of the second yoke 40, which does not house the coil 60, but may be fitted over only a portion of the outer peripheral surface of the second yoke 40.

[0042] In the magnetorheological fluid device 1, in the portion of the first yoke 30 radially sandwiched between the inner circumferential surface of the casing 80 and the outer circumferential surface of the coil 60, there is a portion where the magnetic resistance is maximum in the magnetic path indicated by the dashed arrowed line P that is formed when the coil 60 is energized. Therefore, by positioning the casing 80 in the first yoke 30 so that the portion A1 of the coil-containing region A between the outer circumferential surface of the coil 60 and the inner circumferential surface of the casing 80 is minimized, it is possible to further suppress a decrease in the torque transmitted between the first yoke 30, the second yoke 40, and the rotating plate 20 via the magnetorheological fluid 50 in the magnetorheological fluid device 1.

[0043] (Action and effect) According to the first embodiment of the magnetorheological fluid device 1 described above, the casing 80 made of a non-magnetic material is arranged to cover a portion of the coil 60, and the range in which the outer diameter of the first yoke 30 is reduced is limited, thereby reducing the effect of the casing 80 on the magnetic path and enabling the magnetorheological fluid device 1 to be made smaller while suppressing a decrease in the torque transmitted between components.

[0044] Furthermore, when attaching various sensors such as Hall sensors to the outer peripheral surface of the magnetorheological fluid device 1, by attaching the various sensors to a non-magnetic casing 80, it is possible to eliminate the problems that arise when the various sensors come into contact with a magnetic material.

[0045] Furthermore, when incorporating the magnetorheological fluid device 1 into equipment, if you do not want the magnetic material to come into direct contact with the part of the equipment where it is incorporated (if the magnetic field leaking from the magnetorheological fluid device 1 could have some effect on the function of the equipment), you can suppress the effect of the magnetic field leaking on the equipment by providing a non-magnetic casing 80.

[0046] Furthermore, the non-magnetic casing 80 can also suppress the influence of magnetic fields generated by devices around the magnetorheological fluid device 1 on the magnetorheological fluid device 1.

[0047] Second Embodiment A magnetorheological fluid device 1A according to a second embodiment of the present invention will be described below. In the following description, if the functions of the components constituting each part are the same as those in the magnetorheological fluid device 1 described in the first embodiment, the same reference numerals as in the first embodiment will be used and the description will be omitted even if the shape or the like is slightly different.

[0048] The magnetorheological fluid device 1A according to this embodiment includes a rotating shaft 10, a rotating plate 20, a first yoke 30A, a second yoke 40A, a magnetorheological fluid 50, a coil 60A, and a member 71 for preventing a magnetic short circuit, as shown in FIG.

[0049] In this embodiment, the first yoke 30A and the second yoke 40A function as a single yoke through which a magnetic path formed around the coil 60A, indicated by the dashed arrowed line P, passes. The first yoke 30A and the second yoke 40A are each made of a magnetic material.

[0050] 2, the first yoke 30A is disposed above and radially outward of the rotating plate 20. The first yoke 30A is divided into two parts: a first yoke outer part 310 and a first yoke inner part 320.

[0051] The first yoke outer portion 310 has a disk-shaped first base portion 311 that is centered on the axis N and extends in a direction perpendicular to the axis N, and a cylindrical first extension portion 312 that extends from the radially outer portion of the first base portion 311 toward the second yoke 40A (downward) in the direction of the axis N. The first yoke outer portion 310 has a covered cylindrical shape, with the first base portion 311 serving as a lid portion and the first extension portion 312 serving as a cylindrical wall. A through hole that becomes the first large diameter portion 31b of the shaft hole 31A is formed in the center of the first base portion 311. The axis N passes through the through hole that becomes the first large diameter portion 31b. A bearing 90 is press-fitted into the first large diameter portion 31b and fixed.

[0052] The outer peripheral surface of the first extending portion 312 is provided with an annular step 33A, with the diameter decreasing from the bottom to the top. The portion of the outer peripheral surface of the first extending portion 312 below the step 33A is inserted into and fixed in the casing 80A. In this embodiment, the outer diameter of the first extending portion 312 above the step 33A is set to be approximately equal to the outer diameter of the casing 80A. The outer diameter of the first extending portion 312 below the step 33A is set to be approximately equal to the inner diameter of the casing 80A. The outer diameter of the first extending portion 312 above the step 33A may be larger or smaller than the outer diameter of the casing 80A. The outer diameter of the first extending portion 312 may be smaller on the bottom side, where the casing 80A is fitted, than on the top side. Alternatively, a tapered portion whose diameter decreases from top to bottom may be provided instead of the step 33A.

[0053] An annular groove 301A is provided on the outer peripheral surface of the first extending portion 312 below the step 33A. An O-ring 92 is inserted into the annular groove 301A. The O-ring 92 seals the gap between the first extending portion 312 and the casing 80A. In this embodiment, the inner diameter of the first extending portion 312 is larger than the outer diameter of the coil 60A and the outer diameter of the rotating plate 20 in order to provide a short-circuit magnetic path prevention member 71, which will be described later.

[0054] The first yoke inner portion 320 has a second base portion 321 extending in the direction of the axis N and a second extension portion 322 extending radially outward from a lower portion (the other portion in the direction of the axis N) of the second base portion 321. The second base portion 321 has a generally cylindrical shape and a through-hole formed in its center through which the axis N passes. The through-hole forms the intermediate portion 31a and second large-diameter portion 31c of the shaft hole 31A, and accommodates the rotating shaft 10. The lower surface of the second base portion 321 forms a part of a first opposing surface 34c that faces the first main surface 21 of the rotating plate 20 across a first gap S1.

[0055] The second base portion 321 has an outer peripheral surface 321a, which is the radially outer surface. A coil 60A having a shape that goes around the axis N is arranged around the outer peripheral surface 321a. The coil 60A is formed by winding a coil conductor in a ring shape around the outer peripheral surface 321a. The radial center of the outer peripheral surface 321a coincides with the axis N.

[0056] The second extending portion 322 extends radially outward from the second base portion 321 between the rotating plate 20 and the coil 60A. In this embodiment, the second extending portion 322 expands in a flange-like manner from a lower portion of the second base portion 321. In this embodiment, in order to provide a short-circuit magnetic path prevention member 71 (described later), the outer diameter of the second extending portion 322 is larger than the outer diameter of the rotating plate 20 and smaller than the inner diameter of the first extending portion 312. The lower surface of the second extending portion 322, together with the lower surface of the second base portion 321, forms a first opposing surface 34c that faces the first main surface 21 of the rotating plate 20 with a first gap S1 between them.

[0057] First yoke inner part 320 is inserted through the opening at the bottom of first yoke outer part 310, and first yoke outer part 310 and first yoke inner part 320 are combined and fixed to each other to form first yoke 30A. In first yoke 30A, the through hole of first base part 311 and the through hole of second base part 321 are arranged above and below axis N to form axial hole 31A.

[0058] In the first yoke 30A, the coil accommodating space 35 is formed by the first base portion 311, the first extension portion 312, the second base portion 321, and the second extension portion 322. In this embodiment, the first yoke 30A is divided into two portions, but the division method is not limited thereto, and the first yoke 30A may be divided at other positions. The number of divisions of the first yoke 30A is also not limited to two.

[0059] 2, the second yoke 40A is disposed below the rotating plate 20 such that the rotating plate 20 is interposed between the second yoke 40A and the first yoke 30A. The second yoke 40A has a disk shape that is centered on the axis N and extends in a direction perpendicular to the axis N. The second yoke 40A has a second opposing surface 41A that faces the second main surface 22 of the rotating plate 20 across a second gap S2. The second opposing surface 41A of the second yoke 40A is disposed at a predetermined distance from the first opposing surface 34c of the first yoke 30A.

[0060] The outer diameter of the second yoke 40A is set to be approximately equal to the inner diameter of the portion below the step 33A on the outer peripheral surface of the first extension portion 312 of the first yoke 30A and the inner diameter of the casing 80A. The second yoke 40A is inserted into the casing 80A and fixed to the casing 80A. At this time, the lower end surface of the first extension portion 312 abuts against the upper surface of the second yoke 40A. A magnetic flux passing portion is formed where the upper surface of the second yoke 40A and the lower end surface of the first extension portion 312 abut against each other.

[0061] An annular groove 44 is provided on the outer peripheral surface of the second yoke 40A. An O-ring 92 is inserted into the annular groove 44. The O-ring 92 provides a seal between the second yoke 40A and the casing 80A.

[0062] The magnetorheological fluid 50 is accommodated in a space for accommodating the magnetorheological fluid 50 within the first yoke 30A and the second yoke 40A. The space for accommodating the magnetorheological fluid 50 is a space formed between the first opposing surface 34c of the first yoke 30A and the second opposing surface 41A of the second yoke 40A, excluding the rotating plate 20. In FIG. 2, the space for accommodating the magnetorheological fluid 50 is the area shaded gray. The magnetorheological fluid 50 is present in a first gap S1 between the rotating plate 20 and the first yoke 30A and a second gap S2 between the rotating plate 20 and the second yoke 40A, and transmits torque between them according to its viscosity.

[0063] The coil 60A is formed by winding a coil conductor directly around the outer peripheral surface 321a of the second base portion 321 of the first yoke 30A without using a member such as a bobbin. The coil 60A is accommodated in the coil accommodating space 35 of the first yoke 30A. When a current flows through the coil 60A, a magnetic path is formed that passes through the first yoke 30A, the magnetorheological fluid 50 present in the first gap S1, the rotating plate 20, the magnetorheological fluid 50 present in the second gap S2, the second yoke 40A, and the magnetic flux passing portion along the direction indicated by the dashed arrow line P in FIG. 2. The coil 60A may be configured to use a bobbin.

[0064] The short-circuiting magnetic path preventing member 71 is disposed radially between the inner circumferential surface of the first extending portion 312 and the outer circumferential surface of the second extending portion 322. The short-circuiting magnetic path preventing member 71 is also disposed radially between the inner circumferential surface of the first extending portion 312 and the outer circumferential surface of the coil 60A. The short-circuiting magnetic path preventing member 71 has a substantially cylindrical shape. The short-circuiting magnetic path preventing member 71 is formed of a non-magnetic material. The outer diameter of the short-circuiting magnetic path preventing member 71 is set to be substantially equal to the inner diameter of the inner circumferential surface of the first extending portion 312. The inner diameter of the short-circuiting magnetic path preventing member 71 is set to be substantially equal to the outer diameter of the second extending portion 322.

[0065] The magnetic short-circuiting prevention member 71 prevents a magnetic path that should extend from the first yoke 30A through the magnetorheological fluid 50 present in the first gap S1 and the magnetorheological fluid 50 present in the second gap S2 in the thickness direction of the rotating plate 20 toward the second yoke 40A from being short-circuited to the first extension portion 312 without passing through the first gap S1 and the second gap S2, or without passing through only the second gap S2. The magnetic short-circuiting prevention member 71 may be disposed only between the inner circumferential surface of the first extension portion 312 and the outer circumferential surface of the second extension portion 322 in the radial direction.

[0066] The casing 80A is made of a non-magnetic material such as resin, stainless steel, aluminum, etc. If the casing 80A is made of an insulating material such as resin, it is possible to suppress leakage of current from the magnetorheological fluid device 1A to the outside and the inflow of current from surrounding equipment into the magnetorheological fluid device 1A.

[0067] The casing 80A has a substantially cylindrical shape. The casing 80A is fitted over a portion of the outer circumferential surface of the first yoke 30A and the entire outer circumferential surface of the second yoke 40A. The casing 80A is disposed on the outer circumferential surface of the first yoke 30A so as to cover a portion A1 of the coil-containing region A where the coil 60A is located radially inward, but not cover a remaining portion A2 of the coil-containing region A. Therefore, the outer diameter of the portion of the outer circumferential surface of the first extending portion 312 of the first yoke 30A that corresponds to the portion A1 of the coil-containing region A is smaller than the outer diameter of the portion of the first extending portion 312 that corresponds to the remaining portion A2 of the coil-containing region A. The casing 80A is not limited to a cylindrical shape, and various shapes such as a rectangular tube shape are possible depending on the shape of the magnetorheological fluid device 1A.

[0068] In this embodiment, the height of the casing 80A is approximately half the height of the magnetorheological fluid device 1A, and the entire second yoke 40A and a portion of the first yoke 30A are inserted into the casing 80A. At this time, the upper end of the casing 80A abuts the step 33A. The casing 80A is then fixed to the first yoke 30A and the second yoke 40A with adhesive, bolts, or the like. The first yoke 30A and the second yoke 40A are connected by the casing 80A. At this time, the first yoke 30A and the second yoke 40A may be connected by fixing the lower end of the first extension portion 312 of the first yoke 30A to the second yoke 40A with bolts, or the like. In this case, the casing 80A may simply be attached to the outer circumferential surfaces of the first yoke 30A and the second yoke 40A with adhesive, or the like.

[0069] In this embodiment, the entire second yoke 40A is inserted into the casing 80A, but only a portion of the second yoke 40A, for example, only the upper half of the second yoke 40A, may be inserted into the casing 80A. In this case, an annular step may be provided on the outer peripheral surface of the second yoke 40A to increase the outer diameter of the lower side. In this way, the casing 80A does not need to fit over the entire outer peripheral surface of the second yoke 40A that does not house the coil 60A, but may fit over only a portion of the outer peripheral surface of the second yoke 40A.

[0070] In the magnetorheological fluid device 1A, in the first yoke 30A, a portion radially sandwiched between the inner circumferential surface of the casing 80A and the outer circumferential surface of the coil 60A exists where the magnetic resistance is greatest in the magnetic path indicated by the dashed arrowed line P that is formed when the coil 60A is energized. Therefore, by positioning the casing 80A in the first yoke 30A so that the portion A1 of the coil-encompassing region A between the outer circumferential surface of the coil 60A and the inner circumferential surface of the casing 80A is minimized, it is possible to further suppress a decrease in the torque transmitted between members in the magnetorheological fluid device 1A.

[0071] (Action and effect) According to the second embodiment of the magnetorheological fluid device 1A described above, when attaching various sensors such as Hall sensors to the outer peripheral surface of the magnetorheological fluid device 1A, the various sensors are attached to the non-magnetic casing 80A, thereby eliminating the problems that arise when the various sensors come into contact with a magnetic material.

[0072] Furthermore, when incorporating the magnetorheological fluid device 1A into equipment, if you do not want the magnetic material to come into direct contact with the part of the equipment where it is incorporated (if the magnetic field leaking from the magnetorheological fluid device 1A could have some effect on the function of the equipment), you can suppress the effect of the magnetic field leaking on the equipment by providing a non-magnetic casing 80A.

[0073] Furthermore, the non-magnetic casing 80A can also suppress the influence of magnetic fields generated by devices around the magnetorheological fluid device 1A on the magnetorheological fluid device 1A.

[0074] <Third embodiment> In the magnetorheological fluid device 1 according to the first embodiment, the first yoke 30, which houses the coil 60, has an axial hole 31 for accommodating and supporting the rotating shaft 10, but as shown in Fig. 3, the second yoke 40B, which does not house the coil 60B, may have an axial hole 45 for accommodating and supporting the rotating shaft 10B. Also, in the magnetorheological fluid device 1 according to the first embodiment, the entire second yoke 40 is inserted into the casing 80, but as shown in Fig. 3, only a portion of the second yoke 40B may be inserted into the casing 80B.

[0075] As shown in FIG. 3, the magnetorheological fluid device 1B according to the third embodiment includes a rotating shaft 10B, a rotating plate 20B, a first yoke 30B, a second yoke 40B, a magnetorheological fluid 50, a coil 60B, and a casing 80B.

[0076] The rotating shaft 10B is supported rotatably about the axis N via a bearing 90B press-fitted into a shaft hole 45 formed in the second yoke 40B. The rotating shaft 10B is formed with, in order from the top, a general portion 11B, a first small diameter portion 12B, a flange portion 15B, and a tip portion 16B.

[0077] The first small diameter portion 12B has a smaller diameter than the general portion 11B. The flange portion 15B has a larger diameter than the general portion 11B. The tip portion 16B has a smaller diameter than the first small diameter portion 12B. The tip portion 16B is inserted into a through hole 23B of the rotating plate 20B. A retaining ring 17B is attached to the general portion 11B, so that the downward movement of the rotating shaft 10B along the axis N relative to the bearing 90B is limited.

[0078] Rotating plate 20B, which is a circular disk, has a first main surface 21B located on the lower side and a second main surface 22B located on the upper side. Rotating plate 20B has a through-hole 23B formed in the center. Tip 16B of rotating shaft 10B is inserted into through-hole 23B, and rotating plate 20B rotates integrally with rotating shaft 10B.

[0079] In this embodiment, a space for accommodating a coil 60B is formed within the first yoke 30B. A space for accommodating a bearing 90B and a rotating shaft 10B is formed within the second yoke 40B. The first yoke 30B and the second yoke 40B are fixed to each other via a casing 80B. A space for accommodating a rotating plate 20B and a magnetorheological fluid 50 is formed between the first yoke 30B and the second yoke 40B.

[0080] In this embodiment, the first yoke 30B, which houses the coil 60B, is disposed below the rotating plate 20B, as shown in Fig. 3. The first yoke 30B has an annular groove 32B, centered on the axis N, for arranging the coil 60B. The annular groove 32B opens upward. The radial center of the annular groove 32B coincides with the axis N. The space within the annular groove 32B serves as a space for housing the coil 60B.

[0081] The first yoke 30B has two first opposing surfaces 34a and 34b that face the first main surface 21B of the rotating plate 20B across a first gap S1. The first opposing surface 34a is located radially inward of the annular groove 32B, and the first opposing surface 34b is located radially outward of the annular groove 32B.

[0082] The outer peripheral surface of the first yoke 30B is provided with an annular step 33B, the diameter of which is smaller at the top than at the bottom. The portion of the outer peripheral surface of the first yoke 30B above the step 33B is inserted into and fixed in the casing 80B. The outer diameter of the first yoke 30B above the step 33B is set to be approximately equal to the inner diameter of the casing 80B. The outer diameter of the first yoke 30B below the step 33B is set to be approximately equal to the outer diameter of the casing 80B. The outer diameter of the first yoke 30B below the step 33B may be larger or smaller than the outer diameter of the casing 80B. The outer diameter of the first yoke 30B needs only to be smaller at the top, where the casing 80B is fitted, than at the bottom. Alternatively, a tapered portion whose diameter decreases from bottom to top may be provided instead of the step 33B.

[0083] An annular groove 301B is provided on the outer peripheral surface of the first yoke 30B above the step 33B. An O-ring 92 is inserted into the annular groove 301B. The O-ring 92 seals the gap between the first yoke 30B and the casing 80B.

[0084] 3, the second yoke 40B is provided above the rotating plate 20B so that the rotating plate 20B is interposed between the second yoke 40B and the first yoke 30B. In this embodiment, the second yoke 40B is formed in a substantially annular shape centered on the axis N. The second yoke 40B has a second opposing surface 41B that faces the second main surface 22B of the rotating plate 20B across a second gap S2. The second opposing surface 41B is disposed at a predetermined distance from the first opposing surfaces 34a and 34b of the first yoke 30B.

[0085] The second yoke 40B has a shaft hole 45 in its center for passing the rotating shaft 10B through. A first large-diameter portion 45b, which has an inner diameter larger than that of the intermediate portion 45a, is formed above the intermediate portion 45a of the shaft hole 45. A bearing 90B is press-fitted into the first large-diameter portion 45b and fixed to the second yoke 40B. Furthermore, a second large-diameter portion 45c, which has an inner diameter larger than that of the intermediate portion 45a, is formed below the intermediate portion 45a of the shaft hole 45. The outer periphery of the flange portion 15B of the rotating shaft 10B is inserted into the second large-diameter portion 45c. The inner diameter of the second large-diameter portion 45c is set to be slightly larger than the outer diameter of the flange portion 15B of the rotating shaft 10B.

[0086] When the rotating shaft 10B is inserted from below into the shaft hole 45, the flange 15B of the rotating shaft 10B is inserted into the second large diameter portion 45c. At this time, when the side surface of the flange 15B near the outer periphery abuts against the step between the second large diameter portion 45c and the intermediate portion 45a, the rotating shaft 10B is unable to move upward along the axis N. When the rotating shaft 10B is fixed to the bearing 90B by the retaining ring 17B so as not to move downward along the axis N, the rotating shaft 10B is positioned in the direction of the axis N so as to be rotatable relative to the second yoke 40B. Furthermore, because the rotating plate 20B is fixed to the rotating shaft 10B, the rotating plate 20B is also positioned in the direction of the axis N so as to be rotatable relative to the second yoke 40B.

[0087] A shaft seal member 91B is provided between the inner circumferential surface of the intermediate portion 45a of the shaft hole 45 and the first small diameter portion 12B of the rotating shaft 10B. The shaft seal member 91B seals between the second yoke 40B and the rotating shaft 10B to prevent the magnetorheological fluid 50 (described later) from leaking upward.

[0088] The outer peripheral surface of the second yoke 40B is provided with an annular step 46, the diameter of which is smaller at the bottom than at the top. The portion of the outer peripheral surface of the second yoke 40B below the step 46 is inserted into and fixed to the casing 80B. The position of the step 46 on the second yoke 40B in the direction of the axis N is not particularly limited, and may be within a range that allows the portion of the outer peripheral surface of the second yoke 40B below the step 46 to be inserted into the casing 80B and the casing 80B to be fixed to the second yoke 40B.

[0089] The outer diameter of the second yoke 40B below the step 46 is set to be approximately equal to the inner diameter of the casing 80B. The outer diameter of the second yoke 40B above the step 46 is set to be approximately equal to the outer diameter of the casing 80B. The outer diameter of the second yoke 40B above the step 46 may be larger or smaller than the outer diameter of the casing 80B. The outer diameter of the second yoke 40B needs only to be smaller on the lower side where the casing 80B is fitted than on the upper side, and a tapered portion whose diameter decreases from top to bottom may be provided instead of the step 46.

[0090] An annular groove 44B is provided on the outer peripheral surface of the second yoke 40B below the step 46. An O-ring 92 is inserted into the annular groove 44B. The O-ring 92 provides a seal between the second yoke 40B and the casing 80B.

[0091] The magnetorheological fluid 50 is contained in the space formed between the first opposing surfaces 34a, 34b of the first yoke 30B and the second opposing surface 41B of the second yoke 40B, excluding the rotating plate 20B. In FIG. 3, the space containing the magnetorheological fluid 50 is the area shaded gray. The magnetorheological fluid 50 is present in the first gap S1 between the rotating plate 20B and the first yoke 30B and the second gap S2 between the rotating plate 20B and the second yoke 40B, and transmits torque between them according to its viscosity.

[0092] The coil 60B has a shape that wraps around the axis N and is disposed in the annular groove 32B of the first yoke 30B. In this embodiment, the coil 60B formed by winding a coil conductor and a bobbin 61B are disposed in the annular groove 32B. The coil 60B may not necessarily use the bobbin 61B.

[0093] When a current flows through the coil 60B, a magnetic path is formed that passes through the first yoke 30B, the magnetorheological fluid 50 present in the first gap S1, the rotating plate 20B, the magnetorheological fluid 50 present in the second gap S2, and the second yoke 40B along the direction indicated by the dashed arrow line P in Fig. 3. Then, a magnetic field corresponding to the value of the current applied to the coil 60B is applied to the magnetorheological fluid 50 present in the first gap S1 and the second gap S2.

[0094] The casing 80B is made of a non-magnetic material such as resin, stainless steel, aluminum, etc. If the casing 80B is made of an insulating material such as resin, it is possible to suppress leakage of current from the magnetorheological fluid device 1B to the outside and the inflow of current from surrounding equipment into the magnetorheological fluid device 1B.

[0095] The casing 80B has a substantially cylindrical shape. The casing 80B is disposed radially outward from the outer circumferential surface of the coil 60B so as to fit over a portion of the outer circumferential surface of the first yoke 30B and a portion of the outer circumferential surface of the second yoke 40B. The casing 80B is disposed so as to cover a portion A1 of the coil-containing region A located radially inward of the coil 60B on the outer circumferential surface of the first yoke 30B, but not to cover a remaining portion A2 of the coil-containing region A. Therefore, the outer diameter of the portion of the outer circumferential surface of the first yoke 30B corresponding to the portion A1 of the coil-containing region A is smaller than the outer diameter of the portion of the outer circumferential surface of the first yoke 30B corresponding to the remaining portion A2 of the coil-containing region A. The casing 80B is not limited to a cylindrical shape and can have various shapes, such as a rectangular tube, depending on the shape of the magnetorheological fluid device 1B.

[0096] In this embodiment, the portion of the first yoke 30B above the step 33B and the portion of the second yoke 40B below the step 46 are inserted into the casing 80B. At this time, the lower end of the casing 80B abuts against the step 33B, and the upper end of the casing 80B abuts against the step 46. In this state, the casing 80B is fixed to the first yoke 30B and the second yoke 40B, thereby connecting and fixing the first yoke 30B and the second yoke 40B. In this embodiment, only a portion of the second yoke 40B is inserted into the casing 80B, but the entire second yoke 40B may also be inserted into the casing 80B.

[0097] In the magnetorheological fluid device 1B, a portion of the first yoke 30B radially sandwiched between the inner circumferential surface of the casing 80B and the outer circumferential surface of the coil 60B has a portion where the magnetic resistance is greatest in the magnetic path indicated by the dashed arrowed line P that is formed when the coil 60B is energized. Therefore, by positioning the casing 80B in the first yoke 30B so as to minimize the portion A1 of the coil-containing area A between the outer circumferential surface of the coil 60B and the inner circumferential surface of the casing 80B, it is possible to further suppress a decrease in the torque transmitted between the first yoke 30B, the second yoke 40B, and the rotating plate 20B via the magnetorheological fluid 50 in the magnetorheological fluid device 1B.

[0098] (Action and effect) According to the magnetorheological fluid device 1B of the third embodiment described above, the first yoke 30B and the second yoke 40B are fitted into the casing 80B, respectively, and the casing 80B is fixed by abutting both ends of the casing 80B against the steps 33B, 46, so that the first yoke 30B and the second yoke 40B can be arranged at a predetermined interval.

[0099] By positioning the casing 80B made of a non-magnetic material so as to cover a portion of the coil 60B and limiting the range in which the outer diameter of the first yoke 30B is reduced, the effect of the casing 80B on the magnetic path is reduced, and the magnetorheological fluid device 1B can be made smaller while suppressing a decrease in the torque transmitted between components.

[0100] Furthermore, when attaching various sensors such as Hall sensors to the outer peripheral surface of the magnetorheological fluid device 1B, by attaching the various sensors to a non-magnetic casing 80B, it is possible to eliminate the problems that arise when the various sensors come into contact with a magnetic material.

[0101] Furthermore, when incorporating the magnetorheological fluid device 1B into equipment, if you do not want the magnetic material to come into direct contact with the part of the equipment where it is incorporated (if the magnetic field leaking from the magnetorheological fluid device 1B could have some effect on the function of the equipment), you can suppress the effect of the magnetic field leaking on the equipment by providing a non-magnetic casing 80B.

[0102] Furthermore, the non-magnetic casing 80B can also suppress the influence of magnetic fields generated by devices around the magnetorheological fluid device 1B on the magnetorheological fluid device 1B. [Industrial Applicability]

[0103] The present invention can be applied to a magnetorheological fluid device in which, for example, a magnetorheological fluid is interposed between components that are arranged to be rotatable relative to one another, and the torque transmitted between the components can be changed by changing the strength of the magnetic field applied to the magnetorheological fluid. [Explanation of symbols]

[0104] 1, 1A, 1B Magnetorheological fluid device 10, 10B Rotation axis 20, 20B Rotating plate 21, 21B 1st main surface 22, 22B 2nd main surface 30, 30A, 30B First yoke 31, 31A shaft hole 33, 33A, 33B steps 34a, 34b, 34c 1st opposing surface 310 First yoke outer part 311 1st base 312 1st extension part 320 First yoke inner part 321 Second base 322 Second extension part 40, 40A, 40B Second yoke 41, 41A, 41B 2nd opposing surface 45 shaft hole 46 steps 50 Magnetorheological fluid 60, 60A, 60B coils 70 spacer 71 Short-circuit magnetic path prevention material 80, 80A, 80B casing 90, 90B bearings A Coil-containing region B Bolt N axis P dashed line with arrow S1 First gap S2 Second gap

Claims

1. a rotating plate fixed to a rotating shaft that rotates around an axis; a yoke having a first opposing surface facing one main surface of the rotary plate with a first gap therebetween, and a second opposing surface facing the other main surface of the rotary plate with a second gap therebetween; a magnetorheological fluid filled in the first gap and the second gap; a coil that forms a magnetic path that passes through the yoke, the rotating plate, and the magnetorheological fluid when energized, and is housed within the yoke and has a shape that circles around the axis; Equipped with In the magnetorheological fluid device, the rotating plate is rotatably provided with respect to the yoke, a casing made of a non-magnetic material fitted onto a part of the outer circumferential surface of the yoke; the casing is disposed so as to cover a part of a region (hereinafter referred to as a "coil-containing region") in which the coil is located radially inward on the outer peripheral surface of the yoke, but not to cover the remaining part of the coil-containing region; When viewed from the direction of the axis, the part of the coil-containing region on the outer peripheral surface of the yoke is formed inside the remaining part of the coil-containing region on the outer peripheral surface of the yoke, without being inscribed in the remaining part. A magnetorheological fluid device characterized by:

2. 2. The magnetorheological fluid device according to claim 1, The yoke is a first yoke in which the first opposing surface is formed and in which the coil is housed; a second yoke on which the second opposing surface is formed, the casing is fitted onto the portion of the coil-containing region of the outer circumferential surface of the first yoke and onto at least a portion of the outer circumferential surface of the second yoke. A magnetorheological fluid device characterized by:

3. 3. The magnetorheological fluid device according to claim 2, In the first yoke, a portion of the first yoke that is radially sandwiched between the inner peripheral surface of the casing and the outer peripheral surface of the coil has a portion where magnetic resistance is maximum in a magnetic circuit that is formed when current is applied to the coil. A magnetorheological fluid device characterized by:

4. The magnetorheological fluid device according to any one of claims 1 to 3, The yoke is not disposed between the coil and the rotating plate. A magnetorheological fluid device characterized by:

5. The magnetorheological fluid device according to any one of claims 1 to 3, The yoke portion is disposed between the coil and the rotating plate. A magnetorheological fluid device characterized by:

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