Brakes – Internal-resistance motion retarder – Electroviscous or electrorheological fluid
Reexamination Certificate
1999-09-13
2001-08-28
Graham, Matthew C. (Department: 3613)
Brakes
Internal-resistance motion retarder
Electroviscous or electrorheological fluid
C188S322150
Reexamination Certificate
active
06279700
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 electro-magnetomechanical 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 have been suggested for 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 element 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.
Although the damper disclosed in the '840 application may perform adequately, there is a continuing need for a more compact, higher performance and/or lower cost damper. For example, the damper of the '840 application requires a piston having an unnecessarily long length to form a sufficient surface area in the annular passage against which adequate shear can be generated to permit effective damping control.
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 the annular passage and extending across the inlet/outlet to 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 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. Also, the plate adds to the length of the piston thereby 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 capable of effectively and predictably providing a desired damping effect.
It is another object of the present invention to provide an MR damper having a piston with a minimal length while achieving effective damping.
It is yet another object of the present invention to provide an MR damper which optimizes the surface area along a flow gap formed by the piston thereby enhancing a shearing effect.
It is a further object of the present invention to provide an MR damper which increases shear in an annular flow gap without significantly impeding both fluid flow axially through the gap and a magnetic flux transversely across the gap.
Yet another object of the present invention is to provide an MR damper which effectively and accurately locates a flux ring concentrically on a central piston core to form and maintain an annular flow gap.
It is a still further object of the present invention to provide an MR damper including a flux ring which is simply and inexpensively attached to a piston core.
Still another object of the present invention is to provide an MR damper offering sufficient flexibility to accommodate damper piston to tube misalignment thereby allowing looser manufacturing tolerances.
Yet another object of the present invention is to provide an MR damper which permits a smaller clearance between the damper piston outside diameter and the damper cylinder resulting in less uncontrolled leakage around the piston.
A still further object of the present invention is to provide an MR damper capable of better distributing side loads on the piston thereby lowering wear rates on the piston and the damper cylinder possibly permitting the use of softer and less expensive materials while reducing the plating thickness on the inner surface of the cylinder.
It is yet another object of the present invention to provide an MR damper which avoids the use of mounting plates positioned at the end of the piston for securing a flux ring to the piston core thereby eliminating very costly machined parts.
These and other objects are achieved by providing a damper comprising a cylinder containing a magnetorheological fluid and a piston mounted for reciprocal movement in the cylinder to form a first chamber positioned on one side of the piston and a second chamber positioned on an opposite side of the piston. The piston includes a flow gap extending between the first and the second chambers. The damper also includes a magnet assembly mounted on the piston to generate a magnetic field extending through the flow gap. The damper also includes at least one thin-walled insert positioned in the flow gap to form a first flow gap section on one side of the thin-walled insert and a second flow gap section on an opposite side of the thin-walled insert. The thin-walled insert includes a first surface facing the first flow gap section to generate shear stress on the magnetorheological fluid flowing through the first flow gap section and a second surface facing the second flow gap section to generate shear stress on the magnetorheological fluid flowing through the second flow gap section. The thin-walled insert may be formed of a nonmagnetic material so as not to interfere with the magnetic flux. Also, the thin-walled insert may have a tubular shape to form a flow gap extending annularly around an axis of the piston. The damper may also include at least one end plate mounted on the piston to secure the thin-walled insert against axial and radial movement in the flow gap. The thin-walled insert may include two annular opposing unconnected ends facing one another to form an end gap. The thin-walled insert also may include a thickness extending between the first and second surfaces which is less than a total radial width equal to the sum of a width of both the first and second flow ga
Baudendistel Thomas Allen
Hopkins Patrick Neil
Lisenker Ilya
Oliver Michael Leslie
Delphi Technologies Inc.
Graham Matthew C.
Sigler Robert M.
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