Brakes – Internal-resistance motion retarder – Using magnetic flux
Reexamination Certificate
2001-04-04
2002-09-24
Graham, Matthew C. (Department: 3683)
Brakes
Internal-resistance motion retarder
Using magnetic flux
C137S909000
Reexamination Certificate
active
06454059
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to Magneto-Rheological (MR) devices and more particularly to an improved design for an MR damping device.
BACKGROUND OF THE INVENTION
Devices for suspending parts and controlling or damping their movement relative to one another, are known in the art. For example, such devices are known and used in the automotive field in vehicle suspension systems. The devices might take the form of shocks, struts and other motion or vibration damping devices.
Generally, many such devices utilize fluids for controlling the relative movement of the mechanical parts. For example, hydraulic fluid may be utilized as a medium for creating damping forces or torques or controlling motion, shock and vibrations. One class of such movement control devices utilizes a fluid medium which has characteristics which are controllable through the use of magnetic fields and/or magnetic flux. Such magnetically controlled fluid is referred to as magneto-rheological, or MR, fluid and is comprised of small, soft magnetic particles dispersed within a liquid carrier. The particles are often generally round, and the suitable liquid carrier fluids include hydraulic oils and the like for suspending the particles. MR fluids exhibit a thickening behavior (a rheology change), often referred to as “apparent viscosity change,” upon being exposed to magnetic fields of sufficient strength. The higher the magnetic field strength to which the MR fluid is exposed, the higher the flow restriction or damping force that can be achieved in the MR device, and vice versa. That is, the flow properties of MR fluids may be selectively altered by magnetic fields.
A typical MR damping device, for example, utilizes an iron core structure disposed within or surrounded by a metal cylinder or casing. MR fluid is positioned to flow between the core and the metal cylinder. The damping effect of the device is due to the relative movement of the core and cylinder with respect to the MR fluid or vice versa. That is, depending upon the use and structure of the MR damping device, the core and cylinder are dynamic and move through the MR fluid or the MR fluid moves between a stationary core and cylinder. To control the damping effects of the device, a magnetic flux is formed in and around the core and the metal cylinder, such that the core and cylinder create a magnetic circuit. The metal cylinder or casing surrounding the core is often referred to as a “flux ring” as it directs and provides a path for the magnetic flux which exists in and around the core. Variation of the flux in the device affects the flow of the MR fluid between and around the core and flux ring and thus allows variation of the damping effects of the MR device.
More specifically, during operation of the damping device, the MR fluid flows through a restricted passage or gap formed between the flux ring and the core. Magnetic flux exists within the gap, and therefore, the characteristics of the MR fluid flow through the gap are magnetically controlled by controlling the magnetic flux. By controlling the characteristics of the MR fluid flow, the movement of the core and flux ring relative to the fluid is controlled, thus creating a damping effect to the physical structures which are operably coupled to the MR damping device. To form and vary the magnetic flux in and around the core and within the gap between the core and the flux ring, a magnetic field generator, such as a wire coil is wound around the core. The magnetic flux in the core and in the fluid passage is varied by variation of the electrical current through the coil. The selectively variable magnetic flux dictates the characteristics of the fluid flow in the restricted passage, and the relative movement any mechanical parts and the damping of that movement is then regulated by controlling the characteristics of the fluid flow.
When constructing and assembling a typical MR damping device, as described above, the core and the wire coil which is wound around the core are formed with an insulative material. The material, which may be an insulative plastic material, is molded flush around the coil to protect the coil from the MR fluid. Thereafter, the flux ring, or other metal casing surrounding the core and coil, is placed around the core and coil. Generally, the flux ring is placed concentrically around the core and coil combination to form a fixed annular gap between the flux ring and the core. The MR fluid flows within the gap. As such, it is important to ensure that the gap is generally consistently formed and spaced with respect to the core for uniformity of the damping forces created by the MR damping device. Therefore, the flux ring must be properly located and aligned around the core and coil. In conventional designs of MR damping devices, various fasteners and structures are necessary to provide the proper securement and alignment of the flux ring. For example, non-magnetic hog-rings, needle bearings, and rivets are utilized between the flux ring and the core at three or four positions along the length of the device. Alternatively, two end plates are crimped in place with the flux ring and core for alignment and retention.
While current MR damping devices are suitable to provide the damping forces required, their current design and construction makes them difficult to assemble. Multiple steps are necessary for proper positioning of the elements with respect to each other, particularly with respect to placement of the flux ring. As may be appreciated, multiple steps within a manufacturing and assembly process increase the cost of such a process.
A further drawback to current MR damping device designs is that special fasteners are necessary for locating and aligning the flux ring with respect to the core and coil. Such fastening structures increase the number of parts of the design, providing additional handling and assembly steps and also increasing the cost of the assembly process. Furthermore, using a design with endplates, additional “dead” length occurs along the length of the core and flux ring.
Another particular drawback of the current design is the need for proper location and alignment of the flux ring with respect to the core and coil. It is important that the annular gap has a consistent spacing along the length of the flux ring and core. As may be appreciated, such precise attention to location and alignment of the elements of the MR damping device further increases the assembly steps necessary and thus increases the manufacturing and assembly costs for the device.
The above-mentioned drawbacks of conventional MR damping devices and the manufacture and assembly of same, are further exacerbated by the variations which occur in the assembly due to variations in the various pieces which must be used and aligned. Inconsistency is introduced as a result of batch-to-batch or part-to-part variations of the multiple components which are necessary for construction of the devices. Furthermore, such differences make consistent alignment and location of the components of the device difficult. Of course, all such factors further increase the cost of manufacturing and assembling of the MR damping devices.
Therefore, it is a general objective of this present invention to improve existing MR damping devices, and specifically to improve their design.
It is another objective of the present invention to make such MR damping devices easier and more cost effective to assemble by reducing the assembly steps and also reducing the complexity of such assembly steps.
It is a further objective of the invention to reduce the cost of manufacturing an MR damping device by reducing the number of separate parts which must be handled and utilized in the manufacturing and assembly processes.
It is another objective of the invention to simplify the location and alignment steps associated with certain components of an MR damping device during assembly of such a device.
It is still another objective of the invention to reduce the cost increase in the assembly process which is due to the incons
Ananthanarayanan Venkatasubramanian
Hopkins Patrick N.
Lisenker Ilya
Lonbani Sohrab Sadri
Muhlenkamp John H.
Delphi Technologies Inc.
Graham Matthew C.
McBain Scott A.
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