Brakes – Internal-resistance motion retarder – Electroviscous or electrorheological fluid
Reissue Patent
1998-01-16
2001-01-16
Butler, Douglas C. (Department: 3613)
Brakes
Internal-resistance motion retarder
Electroviscous or electrorheological fluid
C188S322190, C188S322500
Reissue Patent
active
RE037015
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to vibration damping devices which develop damping performance when being applied to a suspension member, such as for automobiles or other equipment. More particularly, the invention relates to such a damping device using an electrorheological (ER) fluid as the damping medium and having a plurality of spaced electrode bands, which device is of a relatively simple structure, easy to assemble and to apply a voltage to the ER fluid contained therein for changing the damping characteristics of the device.
2. Background Information
Vibration damping devices have been used for considerable periods of time to dampen the vibrational forces applied to the suspension system of vehicles to provide a controlled response by reducing the vibrations caused by road bumps and depressions passing from the tires to the vehicle frame by the interposing of oil-filled shock absorbers or high-pressure gas damping devices.
Although these prior art oil and high-pressure gas damping devices have proven satisfactory, a more recent development has evolved in which an electrorheological or electroviscous fluid is used within the chamber of the damping device, wherein the liquid is in contact with one or more electrodes, usually mounted in a restrictive passage, which depending upon the size of the electrodes and the amount of voltage applied to the liquid, will change the viscosity of the liquid, enabling the damping device to have a greater range of performance characteristics than those achieved by the high-pressure gas or oil-filled shock absorbers.
An example of an anti-vibration device which uses an expandable liquid chamber containing an electrorheological fluid is shown in U.S. Pat. No. 4,973,031. U.S. Pat. No. 4,858,733 discloses another damping device using electrodes in combination with an electroviscous liquid contained within closed chambers. The liquid is movable through a restricted passage where voltage is applied to the electroviscous liquid as it moves through the passage to change its viscosity to achieve various damping effects. Various other types of such ER vibration damping devices use elastomeric members or sleeves for containing the ER fluid, such as shown in U.S. Pat. No. 5,180,145. Although these devices have proved satisfactory, they are limited as to the amount of internal pressures available for damping, since the sleeves expand and affect the response time and peak force available.
Therefore, the use of rigid fluid chambers formed of metal have been utilized with ER fluids in order to be able to develop higher internal pressure and quicker response times. U.S. Pat. Nos. 4,819,772 and 5,259,487 are believed to be the closest prior art to the vibration damping device of the present invention. The damping devices of both of these patents use an ER fluid which is contained within rigid housings to provide for increased pressures and quicker response time not believed obtainable with ER dampers using an elastomeric sleeve or bellows for the chamber-forming member.
However, the structures of both of these prior art damping devices require a complicated structure consisting of numerous parts in order to achieve the electrical isolation required for applying a voltage to the restricted orifices or ducts through which the ER fluid moves, and requires the passage of the wires applying the voltage to the electrode to pass through the ER fluid chamber. Likewise, the outer body or housing must be of a rigid metal, since this outer housing is connected at one end directly to one of the spaced vehicle components, and therefore must be of sufficient strength to support the various loads and forces applied thereto. An outer end of the piston rod is connected to the other of the spaced vehicle components for mounting the vibration damping device on the vehicle.
All of the known prior art dampers which use an ER fluid use a single continuous electrode which communicates with the ER fluid. It has been found that by providing a plurality of electrodes spaced within the damper that a greater damping force can be produced with the same equivalent electrode length than that with a continuous electrode with approximately the same electrical current and voltage.
Thus, the need exists for an improved vibration damping device, using ER fluids, which is of a simpler construction, which is able to withstand the various loads and forces exerted thereon when mounted between spaced structural components of a vehicle, and which enables a voltage to be applied to a plurality of spaced electrodes contained within the damping device in an easier manner than existing ER fluid dampers.
SUMMARY OF THE INVENTION
Objectives of the invention include providing an improved damping device using ER fluids, which solves the aforementioned problems of prior art dampers by reducing the complexity of the damper without sacrificing the damping characteristics achieved thereby.
A still further objective of the invention is to provide such a damping device which, when used with an electrorheological of electroviscous fluid, enables the orifice and associated electrode to have various configurations in order to achieve various damping characteristics.
Another objective of the invention is to provide such a damping device which is of a considerably simpler structure than prior dampers using ER fluids, and which is able to withstand the various loads and forces exerted thereon when mounted between spaced components in a vehicle suspension system.
A further objective of the invention is to provide such a damping device in which the electrode for supplying voltage to the ER fluid is mounted outwardly of the ER fluid to eliminate the passing of the electrical wires, which supplies the voltage to the electrode, through the ER fluid, as in prior dampers using ER fluids.
A still further objective of the invention is to provide such a damping device which incorporates a pressurized gas reservoir within the damper to prevent cavitation and the formation of bubbles within the ER fluid, thereby preventing the creation of electrical arcing within the fluid.
Still another objective of the invention is to provide such a damper in which the outer housing can be formed of a dielectric material, with the inner housing which forms the piston chamber being formed of metal, thereby enabling smaller diameter cylinders to be used, and to enable all metal components of the damper except for the electrode, to be grounded, to reduce the risk of electrical shorts or shocks.
A further objective of the invention is to provide such a damper in which the electrode is a plurality of discrete electrode bands spaced along the fluid duct and separated from each other by dielectric bands of material, and in which a single voltage source can apply voltage simultaneously to all of the electrode bands, or in which each electrode band can have its own voltage source applied thereto to provide a greater damping force than that provided by a continuous electrode having the same total electrode length, with approximately the same amount of current used in the continuous length electrode.
Still another objective of the invention is to provide such a damping device which can be easily assembled and disassembled for repair and ease of manufacture without sacrificing the integrity of the device.
Another objective of the invention is to provide such a damping device that provides a greater ER gain and ER effect at lower piston velocities, and in which the current draw is lower at higher piston velocities than with prior ER dampers, which enables using a higher electrical field at higher piston velocities, if needed.
A further objective of the invention is to provide such an improved damping device which is of a rugged, compact, relatively lightweight, simple design, which achieves the stated objectives in a simple and efficient manner.
These objectives and advantages are obtained by the vibration damping device of the present invention, the general nature of which may be stated as including a cylindrical inn
Rensel John D.
Weitzenhof David A.
Bridgestone/Firestone Inc.
Butler Douglas C.
Kingsbury Thomas R.
Sand Michael
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