Magnetorheological fluid devices

Abstract: Magnetorheological (MR) fluid dampers are optimized. Dimensional relationships involved in the flow of magnetic flux are related to an operational parametric ratio of magnetic flux density in the fluid to the flux density in the steel. A magnetic valve is utilized to change the flow parameters of the MR fluid and, hence, the operational characteristics of the damper. Several embodiments depicting improved piston designs, including spool as well as toroidal configurations, are disclosed. In addition, both single and twin-tube housing designs are presented, along with several sealless designs. Baffle plates and toroidal magnetic segments interspersed with flow slots are utilized to increase contact between the fluid and the magnetic coil.

Description: Field of the Invention Incompressible fluids have been used in shock absorbers and other dampers, as well as in elastomeric mounts, for decades. The use of controllable fluids, electrorheological (ER) and magnetorheological (MR) fluids in dampers, was first proposed in the early 1950's by Winslow in U.S. Patent No. 2,661,596. The use of a controllable fluid in a damper affords some intriguing possibilities relative to providing widely varying damping for varying conditions encountered by the damper. Nonetheless, the use of controllable fluids was generally restricted to the area of clutches, with a few exceptions, until the mid-1980's. Background and Summary of the Invention Interest in the use of controllable fluids revived in the 1980's as activity in the area of controllable dampers increased. Most of the resurgent activity has occurred relative to ER dampers and associated fluids. While interest and development of ER fluid devices continues, performance of such systems have been disappointing from three standpoints: 1) the damping forces that can be generated by an ER fluid device are limited due to the relatively low yield strengths of the available fluids; 2) ER fluids are susceptible to contamination which significantly degrades performance; and, 3) the strong electric fields required by ER fluids necessitate complicated and expensive high-voltage power supplies and complex control systems. Faced with these performance restrictions and searching for a technological breakthrough to overcome them, Applicants turned to MR fluids with renewed interest and sought to optimize systems employing them. MR fluids inherently have higher yield strengths and are, therefore, capable of generating greater damping forces. Further, contamination does not pose the performance degradation threat for MR fluids that it does for ER fluids. Still further, MR fluids are activated by magnetic fields which are easily produced by simple, low-voltage electromagnetic coils. It is therefore among the objects of the present invention to provide an MR damper with improved performance characteristics. Enhancements include: defining dimensional/operational relationships which provide improved performance; devising piston designs in which the flow path for the magnetic flux is entirely contained within the piston itself; providing an improved twin-tube cylinder design capable of use (with some modification) with either the self-contained or spool piston; significantly reducing or eliminating MR fluid losses from the damper; providing an improved fluid valve for controlling the flow of the MR fluid to produce the desired damping forces. These and other objects of the invention are accomplished by an apparatus for variably damping motion using an MR fluid. JP-A-58221034 discloses a magnetorheological damper, but it does not include any means of relieving over pressurisation. According to a first aspect of the present invention there is provided apparatus for variably damping motion using a magnetorheological fluid, the apparatus comprising: a) a housing element for containing a volume of magnetorheological fluid, said housing including a first inner tube and a second outer tube; b) means to fluidically interconnect said first and second tubes, said means including at least one opening near a first end of said first and second tubes and at least one second opening near a second end of said first and second tubes; c) a piston mounted upon a piston rod for movement within said first tube; d) valve means for controlling flow of said magnetorheological fluid, associated with at least one of said first and second openings, said valve means including: i) passageway means through which said magnetorheological fluid flows; ii) a magnetic coil for altering at least one flow characteristic of said magnetorheological fluid within said housing element to control a flow rate at which said fluid passes through said passageway means, and e) pressure relief means for preventing fluid pressure build-up within said housing. The housing may be a twin-tube design; the magnet may be formed on a spool-shaped piston or wound as a toroid thereon; the magnet could be positioned within the twin-tube housing rather than on the piston; loss of MR fluid can be prevented by topping the damper with a less dense fluid, using a scraper and seal combination, or using a sealless design. The piston may be formed from conventional ferrous materials (in either solid or laminate form) or from powdered metals. These features may be embodied in a mount as well as in a damper. Brief Description of Drawings Fig. 1(a) is a cross-sectional side view of a first twin-tube housing configuration; Fig. 1(b) is a cross-sectional side view of a second twin-tube housing configuration; and Fig. 1(a) is a cross-sectional side view of a third twin-tube housing configuration employing two magnetic valves; Description of the Preferred Embodiments The three embodiments shown in Figs 1(a) - (c) each employ a twin-tube housing 20 which allow the coil 40 to be located stationarily relative to the housing, thereby minimising flexing of wires. Housing 20 has a first inner tube 17 and a second outer tube 19. Valve member 59 comprises coil 40 which is wrapped around core element 43 and the end of inner tube 17 is stabilised between core element 43 and cup-shaped end member 53 by spacers (not shown) to define the gap g of valve member 59 . Accumulator 23 is incorporated into piston head 34 . As shown, a floating piston 21 can be used to create the accumulator 23 or, as mentioned with respect to earlier embodiments, a rolling diaphragm of a type similar to that taught in U. S. Patent No. 4,811,919 may be used. Any type of accumulator may be used. As the piston 30 experiences a compressive stroke, the MR fluid is a) forced through gap g , which (in conjunction with coil 40 ) functions as a valve, b) into outer tube 19 , c) through openings 68 back into the inner tube 17 . The flow characteristics of MR fluid 18 will be controlled by regulating the current flow in coil 40, as with previous embodiments. Fig. 1(b) shows a similar twin tube housing 20 in which coil 40 is toroidally wound about core 43 in segments with intermittent slots as in the Fig. 8 embodiment of the applicant's European Patent No. 0 644 987. The slots, in conjunction with the coil 40 will function as the valve for the MR fluid 18 in this embodiment. Fig. 1(c) demonstrates a third embodiment of a damper 16 which has a twin tube housing 20. In this embodiment, two coils 40 are used, the lower coil 40 and gap g 1 form the valve for controlling flow of the compressive stroke while upper coil 40 and gap g 2 form the valve for controlling flow on the extension stroke. Lower valve member 59 is depicted as having a baffle plate 58, while upper valve member 59 , which must permit passage of piston rod 32 , is of a modified solenoidal design. Upper and lower check valves 35, which are preferably reed valves that flap open and closed responsive to fluid pressure, provide fluid bypass of upper and lower coils 40 for the compression and extension strokes, respectively. An externally mounted accumulator 23 of the type shown in U. S. patent no. 4,858,898 is used in this embodiment which comprises an elastomeric bladder that may be filled with air or foam rubber. As with the other accumulators, accumulator 23 provides room for additional incompressible MR fluid resulting from displacement by piston rod 32 or from thermal fluid expansion. In this embodiment, no electrical connections are made through piston rod 32 and piston head 34 has a more conventional engagement with inner tube 17 (i.e., no-fluid-flow-past or through). Recesses 37 form pockets which in conjunction with hydraulic end stops 31 trap fluid and prevent piston head 34 from banging into either end cap 64. This double-valve design is particularly useful for dampers generating large forces. In such applications, the use of two valves 59 provides more precise control and reduces the risk of cavitation of the fluid. Further, the forces generated in the compression and extension strokes can be individually tailored to fit the desired design parameters.

Claims: Apparatus (16) for variably damping motion using a magnetorheological fluid, said apparatus comprising: a) a housing element (20) for containing a volume of magnetorheological fluid, said housing including a first inner tube (17) and a second outer tube (19); b) means to fluidically interconnect said first and second tubes, said means including at least one opening (68/g2) near a first end of said first and second tubes and at least one second opening (g/g1) near a second end of said first and second tubes; c) a piston (30) mounted upon a piston rod (32) for movement within said first tube (17); d) valve means for controlling flow of said magnetorheological fluid, associated with at least one of said first and second openings, said valve means including: i) passageway means through which said magnetorheological fluid flows; and ii)a magnetic coil (40) for altering at least one flow characteristic of said magnetorheological fluid within said housing element (20) to control a flow rate at which said fluid passes through said passageway means, the apparatus characterised by : e) pressure relief means (23) for preventing fluid pressure build-up within said housing. The apparatus of Claim 1 wherein said pressure relief means (23) comprises an accumulator for accommodating fluid expansion and fluid displaced by said piston rod (32). The apparatus of Claim 1 or Claim 2, wherein said pressure relief means comprises at least one check valve (35).

Inventors: CARLSON J DAVID, CHRZAN MICHAEL J, JAMES FRANK O, CARLSON, J. DAVID, CHRZAN, MICHAEL, J., JAMES, FRANK O.
Applicants: LORD CORP, LORD CORPORATION
Application year: 1993
Main classification: F16F9
IPC codes: F16F13, F16F9