Brakes – Internal-resistance motion retarder – Magnetic fluid or material
Reexamination Certificate
1999-10-21
2001-11-06
Butler, Douglas C. (Department: 3613)
Brakes
Internal-resistance motion retarder
Magnetic fluid or material
C188S322220
Reexamination Certificate
active
06311810
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetorheological fluid damper and more particularly, to a linear acting fluid damper for a vehicle suspension employing magnetic tuning in connection with a magnetorheological working fluid to effect desired damping levels.
BACKGROUND OF THE INVENTION
Magnetorheological fluids that comprise suspensions of magnetic particles such as iron or iron alloys in a fluid medium are well known. The flow characteristics of these fluids can change by several orders of magnitude within milliseconds when subjected to a suitable magnetic field due to suspension of the particles. The ferromagnetic particles remain suspended under the influence of magnetic fields and applied forces. Such magnetorheological fluids have been found to have desirable electromagnetomechanical interactive properties for advantageous use in a variety of magnetorheological (MR) damping devices, such as rotary devices including brakes and clutches, and linear-acting devices for damping linear motion or for providing controllable dissipative forces along the damper's axis.
In particular, linear acting MR dampers are commonly used in suspension systems, such as a vehicle suspension system and vehicle engine mounts. PCT patent application 10840, published Jan. 8, 1998 (the '840 application), discloses a conventional linear acting controllable vibration damper apparatus which includes a piston positioned in a magnetorheological fluid-filled chamber to form upper and lower chambers. The piston includes a coil assembly, a core, i.e. pole pieces, and an annular ring clement positioned around the pole pieces to form an annular flow passage for permitting flow of the magnetorheological fluid between the chambers. When the piston is displaced, magnetorheological fluid is forced through the annular flow passage. When the coil is energized, a magnetic field permeates the channel and excites a transformation of the magnetorheological fluid to a state that exhibits damping forces.
In damper designs utilizing an annular flow passage, the radial width of the annular flow passage must be precisely set and maintained along the axial length of the passage throughout operation to ensure optimum, predictable control of the damping performance. The '840 application discloses the use of a plurality of bridge elements interconnecting the pole piece and the annular ring element. The bridge elements may include circumferentially spaced welds formed of nonmagnetic material. Also, each bridge may include a nonmagnetic pin to further locate and retain the pole relative to the ring. In another embodiment, the pole and ring are connected using a nonmagnetic plate positioned at one end of the assembly. The plate includes radially extending tabs forming bridging elements positioned outside and immediately adjacent the annular passage so as to extend across one end of the annular passage. The plate is secured to the pole piece and the ring by spot welds.
However, the means for connecting the ring and pole piece of the damper disclosed in the '840 application may result in specific disadvantages. For example, the plate tabs and welds are undesirably positioned immediately adjacent one end of the annular flow gap and, therefore, necessarily block fluid flow into the gap along the extent of the tabs and welds thereby disadvantageously reducing the effective shearing surface area of the damper resulting in a reduction in the MR effect. Also, the welds, pins and radial tabs of the plate each include blunt surfaces exposed to the fluid flow that undesirably impede the flow and increase uncontrollable drag forces which lead to a reduction in turn-up ratio performance of the assembly. In addition, both the welds and the plate extend beyond the axial extent of the piston thereby adding to the length of the piston and resulting in an undesirably large and costly assembly possibly incapable of meeting the packaging constraints of a particular application.
Therefore, there is a need for a more compact, less costly MR damper capable of effectively and controllably damping motion.
SUMMARY OF THE INVENTION
It is an object of the present invention, therefore, to overcome the disadvantages of the prior art and to provide a magnetorheological (MR) fluid damper which effectively maintains axial and radial alignment between a flux ring and a piston core while effectively and predictably providing a desired damping effect and minimizing the size and cost of the damper.
This and other objects of the present invention are achieved by providing a damper comprising a cylinder containing a magnetorheological fluid and a piston assembly mounted for reciprocal movement in the cylinder to form a first chamber positioned on one side of the piston assembly and a second chamber positioned on an opposite side of the piston assembly. The piston assembly includes a piston core, a magnet assembly adapted to generate a magnetic field and including a flux ring, and a flow gap extending axially between the first and the second chambers and positioned radially between the core and the flux ring. The piston assembly further includes a connector device formed of a nonmagnetic material including an inner portion connected to the piston core, an outer portion connected to the flux ring and flow passages positioned radially between the outer portion and the inner portion and extending axially to allow fluidic communication between the flow gap and the first chamber. The outer portion includes an abutment surface positioned in abutment with the flux ring while the abutment surface extends annularly along a substantial portion of a circumference of the flux ring. The inner portion may be connected to the piston core by axial compressive forces or by a welded or brazed connection. The outer portion may also be connected to the flux ring by a welded or brazed connection. The connector device may further include at least one bridge portion connecting the inner and the outer portions wherein the bridge portion is positioned a spaced axial distance from the flow gap to form an inlet cavity providing unobstructed fluid flow to the flow gap. The damper may further include a radial support device positioned within the flow gap for radially supporting the flux ring relative to the piston core. The radial support device is preferably positioned entirely within the axial extent of the piston assembly. The radial support device may include rivets secured to one of the flux ring and the piston core wherein the rivets extend radially through the flow gap. The radial support device may include a plurality of balls positioned in the flow gap. A plurality of annular ball seats may be provided on one of the flux ring and the piston core wherein each ball seat is sized to engage a respective ball and prevent axial movement of the ball. The radial support device may further include an aperture formed in the flux ring wherein the ball seat is formed at one end of the aperture. The magnet assembly may include a bobbin and a coil mounted on the bobbin. The radial support device may include tabs integrally formed on the bobbin and positioned in the flow gap. Alternatively, the radial support device may include a washer positioned axially adjacent the coil and including tabs extending into the flow gap. The radial support device may alternatively include elongated pins bonded to the core. The elongated pins may include a rectangular cross section bonded to the piston core by a brazed connection.
The present invention is also directed to a damper comprising a cylinder containing a magnetorheological fluid in a piston assembly mounted for reciprocal movement in the cylinder to form a first chamber positioned on one side of the piston assembly and a second chamber positioned on an opposite side of the piston assembly wherein the piston assembly includes a piston core, a magnet assembly adapted to generate a magnetic field and including a flux ring, and an annular flow gap extending axially between the first and the second chambers and positioned radiall
Alexandridis Alexander Apostolos
Fehring John David
Hopkins Patrick Neil
Kruckemeyer William Charles
Lisenker Ilya
Butler Douglas C.
Delphi Technologies Inc.
Nguyen Xuan Lan
Sigler Robert M.
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