Magnetorheological brake with integrated flywheel

A magnetorheological brake includes an outer, rotating flywheel member having a hollow interior space, and an inner fixed member disposed in the hollow interior space. The inner fixed member is sized so that a working space is provide between the surfaces of the fixed member and the inner wall of the rotating member. A controllable medium of magnetically permeable metal particles is disposed in the working space. A field generator is mounted in the interior space to the fixed member to selectably generate a field acting on the outer and inner members and the controllable medium in the working space. The rheology change in the medium produced by the field generates resistance to rotation of the outer member about the inner member. A device according to the invention may be used as a flywheel/brake or resistance-generating device in exercise equipment, rotating equipment, such as conveyors, and vehicles.

FIELD OF THE INVENTION
 The invention relates to the area of braking, resistance generating, and
 motion control devices. Specifically, it relates to devices employing a
 controllable medium for motion resistance generation in rotating
 mechanisms.
 BACKGROUND OF THE INVENTION
 Magnetorheological (MR) devices for damping and controlling vibration and
 shock are known. MR devices may be of the "rotary-acting" or
 "linear-acting" variety, and can advantageously provide variable
 controlled torques or forces, as the case may be. Known MR devices include
 linear dampers, rotary brakes, and rotary clutches.
 MR fluid devices, for example, typically include a housing or chamber that
 contains a quantity of magnetically controllable fluid, with a movable
 member, a piston or rotor, mounted for movement through the fluid in the
 housing. The housing and the movable member both include a magnetically
 permeable pole piece. A magnetic field generator (a coil or permanent
 magnet) produces a magnetic field across both pole pieces for directing
 the magnetic flux to desired regions of the controllable fluid.
 MR fluid devices employ a Magnetorheological (MR) fluid comprised of
 soft-magnetic particles dispersed within a liquid carrier. Typical
 particles include carbonyl iron, and the like, having various shapes, but
 which are preferably spherical and have mean diameters of between about
 0.1 .mu.m to about 500 .mu.m. The carrier fluids include low viscosity
 hydraulic oils, and the like. In operation, these MR fluids exhibit a
 thickening behavior (a rheology change) upon being exposed to a magnetic
 field. The higher the magnetic field strength in the fluid, the higher the
 damping/restraining force or torque that can be achieved within the MR
 device.
 MR fluid devices are disclosed in U.S. patent application Ser. No.
 08/304,005 entitled "Magnetorheological Fluid Devices And Process Of
 Controlling Force In Exercise Equipment Utilizing Same", U.S. patent
 application Ser. No. 08/613,704 entitled "Portable Controllable Fluid
 Rehabilitation Devices", U.S. application Ser. No. 08/674,371 entitled
 "Controllable Brake", U.S. patent application Ser. No. 08/674,179 entitled
 "Controllable Vibration Apparatus" and U.S. Pat. Nos. 5,547,049,
 5,492,312, 5,398,917, 5,284,330, and 5,277,281, all of which are commonly
 assigned to the assignee of the present invention.
 U.S. Pat. No. 3,962,595 to Eddens discloses a "Magnetic Particle Brake",
 commonly referred to as "Dry Particle Brakes" that includes a rotating
 member that is disposed in an annular space in a stationary member. A
 field-generating coil is mounted in an outer part of the stationary
 member. Magnetic particles are disposed in a space between the inner part
 of the stationary member and the rotating member. Other magnetic particle
 brakes are disclosed in U.S. Pat. No. 4,350,913 to Eddens and U.S. Pat.
 No. 4,575,103 to Pedu.
 Exercise machines such as stationary bicycles, rowers, stair climbers, and
 ski machines, typically rely on some kind of resistance generating device
 to provide adjustable resistance to the exercise movements of the user.
 Conventional resistance systems used in exercise machines, for example,
 friction devices, have deficiencies in providing reliable control of the
 resistance setting and in duration over repeated use of the machine.
 Before the present invention, however, there has been no resistance device
 for exercise machines using MR technology to replace conventional
 resistance devices and provide improved performance, reliability and
 endurance characteristics.
 The foregoing illustrates limitations known to existing present devices and
 methods. Thus, it is apparent that it would be advantageous to provide an
 alternative directed to overcoming one or more of the limitations set
 forth above. Accordingly, a suitable alternative is provided including
 features more fully disclosed hereinafter.
 SUMMARY OF THE INVENTION
 The present invention provides a Magnetorheological (MR) device which
 combines a rotary brake with a flywheel thereby providing both resistance
 and rotational inertia, and can be used in an exercise apparatus and/or as
 a brake for rotating equipment and vehicles.
 According to a preferred embodiment of the invention, a rotary brake device
 comprises an outer rotating member having a hollow interior space and an
 inner stationary member disposed in the hollow space. The rotating member,
 or rotor, rotates around the stationary member, or stator, an arrangement
 contrary to conventional practice. The stator is sized so that a small
 working space exists between the inner wall of the rotor and the
 peripheral surface(s) of the stator. The stator supports a field
 generating device, preferably a magnetic field producing coil. A
 controllable medium (a MR fluid or dry powder) is disposed in the working
 space so that the medium can be acted upon by the field generating device.
 In addition, each of the rotor and the stator is made to include a
 magnetically permeable portion that acts as a pole piece. Rotation of the
 rotor distributes the controllable medium about the inner circumference of
 the rotor.
 Thus, according to the invention, resistance to rotation can be generated
 and preferably controlled by applying a magnetic field to the pole pieces
 and to the controllable medium in the working space. The field causes the
 controllable medium to thicken (a rheology change), which produces the
 resistance to rotation of the rotor relative to the stator.
 The inventor has discovered that a controllable medium of dry powder of
 magnetically permeable material, such as carbonyl iron, provides a
 significantly high resistance force. A controllable medium formed of 410
 stainless steel powder of 325 mesh particles (less than 45 microns in
 diameter) has been found to be particularly effective in a brake according
 to the invention, and has endured a test program of sixteen million cycles
 without failure.
 The controllable medium optionally can be formed of soft-magnetic material
 particles included in a low-viscosity carrier of hydraulic oil.
 The flywheel resistance device of the invention can be incorporated in
 exercise devices, such as bicycles, rowing machines, step machines, and
 ski machines to provide controllable, variable resistance, or in other
 devices/apparatus where it is desirable to have combinations of rotational
 inertia and resistance.
 Alternatively, a device in accordance with the invention may be formed as a
 stationary shaft disposed in a tubular outer member, which may be useful
 as a brake for a conveyor system or a resistance device for a ski machine,
 for example.
 The above-mentioned and further features, advantages, and characteristics
 of the present invention will become apparent from the accompanying
 descriptions of the preferred embodiments and attached drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 Referring now to the Drawings where like numerals denote like elements,
 FIG. 1 illustrates a brake device 18 according to the invention
 integrating a flywheel with a magnetorheological brake mechanism. The
 device 18 includes a flywheel body 20 having a substantially circular
 profile, which is mounted on a shaft 24 for rotation. The flywheel body 20
 includes a radially outward peripheral wall 26, a radially extending side
 wall 28, and a seal 67 that cooperate to define an interior space 22. The
 flywheel body 20 has a rotational inertial mass distribution sufficient to
 act as a flywheel to store energy when set in rotational motion. By way of
 example, and not to be considered limiting, a rotational inertia greater
 than about 0.01 KgM.sup.2 has been determined by the inventor to provide
 the appropriate feel when applying moderate resistance to the brake 18,
 such as would be experienced during use within an exercise machine such as
 a stationary bike. Additional mass may be added to increase the inertial
 mass of the flywheel body 20, for example, in the form of an annular ring
 30 attached to the radially outer wall 26 as shown in FIG. 1.
 A stationary member, or stator 40, is disposed in the interior space 22 of
 the flywheel body 20 and is mounted to a hub 34 which is connected to a
 support structure 42, for example, a frame of an exercise machine. The hub
 34 includes sealed bearings 44 mounted therein which support the shaft 24
 which passes through the hub 34. The shaft 24 includes a coupling 50 to
 interconnect it to a drive source (not illustrated in FIG. 1), for
 example, a pedal apparatus, steps on a stair stepper, rollers on a ski
 machine. Preferably, the drive train interconnected to coupling 50 will
 include a one-way clutch mechanism. Optionally, the one-way clutch may be
 integrated into the coupling 50. The stator 40 is sized so that one or
 more working spaces 46 are provided between the outer, peripheral surfaces
 41 of the stator 40 and the inner wall 43 of the flywheel body 20. Thus,
 as may be understood, the flywheel body 20 surrounds and rotates about the
 stator 40.
 According to the invention, a controllable medium 48 is disposed in the
 working space(s) 46 and the device 18 includes field generating means 60
 for generating a magnetic field that acts between the flywheel body 20 and
 the stator 40 and on the working space(s) 46. By activating the field
 generating means 60, a change in the rheology of the controllable medium
 48 is effected, the controllable medium becoming increasing "thick" in
 response to increasing field strength. The controllable medium 48
 therefore can be controlled to provide selectable resistance to rotation
 of the flywheel body 20 about the stator 40.
 In the illustrated embodiment, the field generating means 60 comprises a
 magnetic field coil mounted to the stator 40, and connected to an external
 controller and power source by wires 62. The stator 40 is formed with pole
 piece halves 45 which cooperate to form an annular groove 63 to
 accommodate the coil 60. In FIG. 1, the stator 40 is illustrated as being
 shaped similar to a tire rim to provide the groove 63. Alternatively, the
 field generating means 60 may be a ring magnet mounted to the stator 40 in
 a manner similar to the coil 60 to provide a continuous resistance brake.
 Other orientations of mounting coils and/or magnets would be apparent.
 Both the stator 40 and the flywheel body 20 include magnetically permeable
 (i.e., soft magnetic) material, such as low carbon steel, to provide pole
 pieces for the field generating means 60. The stator 40 and the flywheel
 body 20 may both be made entirely of a magnetically permeable material.
 Alternatively, the magnetically permeable material may be included in
 portions of the stator 40 and the flywheel body 20 which are to be acted
 upon by the field generating means 60. Preferably, the hub is made from
 aluminum or another nonmagnetic material.
 The inventor has found that a dry powder of stainless steel provides an
 advantageous controllable medium 48. Preferably, the controllable medium
 is a powder of water atomized 410 stainless steel of 325 mesh
 (approximately 45 microns or smaller particle size). The powder medium is
 disposed in the working space(s) 46. Rotation of the flywheel body 20
 readily distributes the powder throughout the working space(s) 46 adjacent
 to the inner periphery 43 of the radially peripheral wall 26.
 The controllable medium 48 may alternatively be formed as a suspension of
 magnetically soft particles in a liquid carrier, as disclosed in, for
 example, U.S. Pat. Nos. 5,382,373 and 5,578,238.
 A skirt 64 is mounted on flywheel body 20 opposite the side wall 28 to help
 prevent the controllable medium 48 from packing near the bearings 44. In
 addition, an elastomeric or plastic seal 67 is formed on (preferably
 pressed into) the hub 34 to seal the interior space 22 of the flywheel
 body 20 and prevent escape of the medium 48.
 In performance testing, a flywheel brake 18 as described using a dry powder
 medium has achieved in excess of 16 million cycles rotating under constant
 applied current. The longevity is at least partially attributed to the
 rotation of the flywheel body 20 which provides a heat sink mass to cool
 the medium 48 in the working space(s) 46. Being the outward positioned
 body, heat in the flywheel body 20 is readily transferred to the
 environment. Fins or other cooling mechanisms could be placed on the
 flywheel body 20.
 The flywheel brake 18 is most advantageous for use in exercise equipment.
 The high rotary inertia of a flywheel 20 imparts smoothness to the moving
 parts of the equipment. The resistance generated by the brake 18 simulates
 resistance encountered in the real-life equivalent to the exercise
 machine. For example, in a stationary bicycle, where exertion of the user
 in pedaling turns the flywheel, rotational inertia of the flywheel
 approximates the feeling of pedaling a bicycle up to speed and maintaining
 it in motion. Continuing with the exercise bicycle example, brake
 resistance simulates rolling friction, air resistance, and gravity (when
 climbing a hill). The flywheel brake 18 may also be used as a brake in
 rotating equipment or in vehicles where combinations of rotary inertia and
 variable resistance are needed. Other uses will occur to those skilled in
 the art.
 FIG. 2 illustrates an embodiment of the magnetorheological brake 118 with
 an integrated flywheel 120 in which a roller, for example, a conveyor or
 exercise machine roller, is the rotating body. The flywheel roller 120 is
 formed as a tube, having a length 1 that is greater than its diameter d,
 and having a hollow interior space 122. The mass of the flywheel roller
 120 may be selected to provide a rotational inertial mass sufficient for
 storing rotational energy. A fixed supporting shaft 124 is disposed in the
 interior space of the roller 120 and is sized so that a working space(s)
 146 is provided between the shaft 124 and an inner surface 143 of the
 flywheel roller 120. Ball bearings 144 support the roller 120 for rotation
 about the shaft 124. The shaft 124 is mounted to the conveyor frame 142 or
 other like frame member, such as a bicycle trainer frame or ski machine
 frame.
 Field generating means are carried/mounted on the shaft 124. The shaft 124
 includes two circumferential grooves 163 in which are mounted coils 160
 for generating fields to act between the shaft 124 and the roller 120 and
 on the working space(s) 146, the magnetic flux being carried in the shaft
 124 and roller 120. Of course, depending on the length of the shaft 124
 and the roller 120, and the desired braking force, the field generating
 means may be suitably adapted, for example, to include one coil for a
 short shaft, or a plurality of coils for a long device. A controllable
 medium 148, such as a dry powder or MR fluid, is disposed in the working
 space 146.
 The fields generated by the coils 160 act on the shaft 124, roller 120 and
 controllable medium 148 and create resistance to rotation of the roller
 120. The roller brake 118 can be used in conveyer systems or other similar
 applications. A roller brake 118 can also be used as a resistance
 generating device in exercise equipment where the user's movements act to
 move the roller 120, as in ski machines, and rollers for bicycles. In the
 case of the ski machine, one or more rollers 120 would be disposed under,
 and in contact with, the ski for rotation upon skiing movements by the
 user. In the rollers for bicycles application, one or more of the rollers
 120 would be positioned to contact a bicycle wheel.
 In summary, it should be apparent from the foregoing that the present
 invention comprises a novel controllable device that combines a rotational
 energy storing flywheel with an integrated brake that can be used in a
 variety of applications. The invention also provides a novel controllable
 medium, a dry powder of soft-magnetic particles or MR fluid that provides
 superior performance and endurance in a flywheel brake device as
 described.
 While several embodiments including the preferred embodiment of the present
 invention have been described in detail, various modifications,
 alterations, changes, and adaptations to the aforementioned may be made
 without departing from the scope of the present invention defined in the
 appended claims. It is intended that all such modifications, alterations,
 and changes be considered part of the present invention.