Brakes – Internal-resistance motion retarder – Electroviscous or electrorheological fluid
Reexamination Certificate
2000-03-31
2001-09-18
Graham, Matthew C. (Department: 3613)
Brakes
Internal-resistance motion retarder
Electroviscous or electrorheological fluid
C188S352000, C267S064280
Reexamination Certificate
active
06290033
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a system for charging magnetorheological (MR) dampers with magnetorheological fluid and other damper components and, more particularly, to a system for effectively loading damper components into a damper cylinder during assembly while minimizing MR fluid leakage.
BACKGROUND OF THE INVENTION
Magnetorheological fluids that comprise suspensions of magnetic particles such as iron or iron alloys in a fluid medium have flow characteristics that 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) devices, such as brakes, clutches, mounts and dampers.
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 proposed 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. A gas cup or diaphragm is positioned at one end of the cylinder to form a pressurized accumulator to accommodate fluid displaced by the piston rod as well as to allow for thermal expansion of the fluid. When the piston is displaced, magnetorheological fluid is forced through the annular flow passage. When the coil is energized, a magnetic field permeates the annular flow passage and excites a transformation of the magnetorheological fluid to a state that exhibits damping forces.
During assembly of a MR damper, magnetorheological fluid is typically injected into a charging assembly and loaded, along with the piston assembly, into the cylinder forming the damper chambers. If included, accumulator gas and a gas cup or diaphragm must also be injected and loaded into the cylinder. A conventional charging assembly includes a charging tube, a set of fill holes and valves for controlling MR fluid and gas flow through the holes. It has been found that MR fluid leakage can occur in the gap around the valve and corresponding hole during movement of the components from the charging assembly into the damper cylinder. This undesirable leakage can accumulate to significant amounts disadvantageously resulting in unacceptable, expensive MR fluid usage and increased clean-up costs.
Therefore, there is a need for a simple, effective and low cost charging system for charging a MR damper with MR fluid without undesirable leakage.
SUMMARY OF THE INVENTION
It is an object of the present invention, therefore, to provide a magnetorheological (MR) fluid damper charging system which effectively charges a MR damper with MR fluid and damper components while minimizing undesirable MR fluid leakage.
This and other objects of the present invention are achieved by providing a magnetorheological damper charging system comprising a charging body including a bore for receiving a damper piston and at least one inlet formed in the charging body for delivering magnetorheological fluid to the bore. The damper charging system also includes a magnetic field generating assembly mounted at the inlet and operable in an energized state to generate a magnetic field across at least a portion of the inlet to cause magnetorheological fluid in the portion of the inlet to experience a magnetorheological effect sufficient to prevent leakage flow through and from the inlet and in a de-energized state to permit fluid flow through the inlet. The charging system may also include a magnetorheological fluid supply and an inlet valve mounted at the inlet for controlling fluid flow from the fluid supply through the inlet into the bore. The inlet valve may be mounted for reciprocal movement between a closed position substantially blocking flow through the inlet and an open position retracted from the inlet. A clearance gap is positioned between the inlet valve and the charging body when the inlet valve is in the closed position so that the magnetorheological effect is experienced in the clearance gap.
The magnetic field generating assembly may include a coil mounted on the inlet valve, and the inlet valve may include a pin element extending through the coil and formed of a magnetic material. The pin element may include a tip portion positionable in the inlet when the valve is in the closed position. The magnetic field generating assembly may further include a nonmagnetic sleeve mounted on the inlet valve axially between the coil and the tip potion.
The system may include a first inlet for delivering magnetorheological fluid to the bore and a second inlet for delivering an accumulator fluid. A first inlet valve may be mounted on the charging body adjacent the first inlet while a second valve is mounted adjacent the second inlet. Each of the first and second inlets includes a clearance gap in which the magnetorheological effect is generated to prevent magnetorheological fluid from leaking from the respective clearance gap.
The present invention is also directed to a method of charging a magnetorheological damper with magnetorheological fluid, comprising the steps of providing a charging body including a bore for receiving a damper piston and at least one inlet formed in the charging body for delivering magnetorheological fluid to the bore. The method further includes the steps of providing a valve at the inlet for controlling flow through the inlet and opening the valve to permit magnetorheological fluid flow through the inlet into the bore. The method also includes the steps of closing the valve to block magnetorheological fluid flow through the inlet and generating a magnetic field across at least a portion of the inlet to cause magnetorheological fluid in at least a portion of the inlet to experience a magnetorheological effect sufficient to prevent leakage from the inlet. The method may further include the steps of inserting a damper piston into the charging body, displacing the damper piston and the magnetorheological fluid from the bore and eliminating the magnetic field from the inlet.
REFERENCES:
patent: 5601164 (1997-02-01), Ohsaki et al.
patent: 5956951 (1999-09-01), O'Callaghan
Delphi Technologies Inc.
Graham Matthew C.
McBain Scott A.
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