Abstract:
A novel and improved magnetorheological (MR) damper charging system is provided which simply and effectively substantially minimizes MR fluid leakage during a MR damper assembly process thereby minimizing cleanup and reducing costs. The damper charging system includes a charging body having a bore for receiving damper components and damper fluid, at least one inlet formed in the charging body for delivering fluid to the bore, and a magnetic field generating assembly mounted at the inlet and operable in an energized state to generate a magnetic field across the inlet to cause MR fluid in the inlet to experience a MR effect sufficient to prevent leakage flow through and from the inlet. An inlet valve is mounted on the charging body for controlling flow of fluid through the inlet into the bore. The magnetic field generating assembly is positioned to generate magnetic flux within a clearance gap between the valve and the inlet walls thereby blocking flow and preventing leakage through the clearance gap as the MR damper components move past the inlet.

Description:
RELATED APPLICATION 
     The present application is related to a U.S. patent application Ser. No. 09/540,583 filed Mar. 31, 2000 and entitled “Magnetorheological Fluid Pumping System, the disclosure of which is incorporated by reference. 
    
    
     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 &#39;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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is an end view of the MR damper charging system of the present invention; 
     FIG. 1 b  is a cross-sectional view of the MR damper charging system of the present invention taken along plane  1   b — 1   b  in FIG. 1 a ; 
     FIG. 1 c  is an expanded view of the area A of FIG. 1 b ; 
     FIG. 2 is a cross-sectional view of the MR damper charging system of the present invention with the inlet valves in the open position; 
     FIG. 3 is a cross-sectional view of the MR damper charging system of the present invention with the inlet valves in the closed position; 
     FIG. 4 a  is an expanded cross-sectional view of the tip portion of the inlet valve of FIG. 3 in the closed position; and 
     FIG. 4 b  is a cross-sectional view of the tip portion of the valve taken along plane  4   b — 4   b  in FIG. 4 a.   
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 a - 1   c,  there is shown the magnetorheological fluid damper charging system of the present invention, indicated generally at  10 , designed to effectively minimize leakage of magnetorheological (MR) fluid from the system during filling of the system with magnetorheological fluid and charging an MR damper with magnetorheological fluid and damper components by displacing the fluid and components from the charging system into an MR damper cylinder  12 . MR damper charging system  10  generally includes a charging body  14  for engaging damper cylinder  12 , a first inlet valve  16  for controlling MR fluid flow into charging body  14  and a first magnetic field generating assembly  18  for reducing MR fluid leakage as discussed more fully hereinbelow. 
     Specifically, referring to FIG. 1 b,  charging body  14  includes a longitudinal bore  20  extending therethrough for receiving a damper piston  22  for subsequent displacement out of charging body  14  into damper cylinder  12 . During assembly, bore  20  may also receive other damper components, such as a gas cup  24  and a seal cover assembly  26 , depending on the type of damper to be assembled. Gas cup  24  will function in the assembled damper as a floating piston separating a MR fluid chamber from a pressurized accumulator volume. The floating piston and accumulator volume of, for example, gas, is necessary to accommodate fluid displaced by piston rod  23  as well as to allow for thermal expansion of the MR fluid thereby permitting effective operation of the assembled MR damper. Of course, damper piston  22  may be any conventional damper used in magnetorheological damping devices while gas cap  24  may be any barrier conventionally used to separate the accumulator chamber from the MR fluid chamber, such as a flexible rolling diaphragm. 
     MR damper charging system  10  also includes a first inlet  28  in the form of a passage communicating at one end with bore  20  and at an opposite end with a MR fluid supply circuit  30  as best shown in FIGS. 1 b  and  2 . A second inlet  32  is positioned a spaced axial distance along bore  20  from first inlet  28  and likewise communicates with bore  20  at one end while communicating with an accumulator gas supply circuit  34  at an opposite end. First inlet valve  16  is mounted for reciprocal movement in a valve block  36  mounted on charging body  14 . Charging system  10  also includes a second inlet valve  38  mounted for reciprocal movement in a second valve block  40  secured to charging body  14  adjacent second inlet  32 . First and second inlet valves  16 ,  38  operate in substantially the same manner to control MR fluid and gas flow, respectively, through first and second inlets  28 ,  32 . Specifically, as discussed more fully hereinbelow, first and second inlet valves  16 ,  38  are moved between a closed position (FIG. 1 b ) blocking fluid and gas flow through the respective first and second inlets  28 ,  32  and an open position (FIG. 2) permitting fluid and gas flow through the inlets. First and second inlet valves  16 ,  38  may be operated by any conventional actuating device capable of selectively and effectively moving the valves between the open and closed positions. 
     Importantly, MR damper charging system  10  of the present invention also includes magnetic field generating assembly  18  associated with first inlet valve  16  and a magnetic field generating assembly  42  associated with second inlet valve  38 . The specific structure of first inlet valve  16  and magnetic field generating assembly  18  will now be discussed in detail. A construction of second inlet valve  38  and magnetic field generating assembly  42  is identical to first inlet valve  16  and magnetic field generating assembly  18  and, therefore, although the valve structure is most clearly shown in FIG. 1 c  with respect to second inlet valve  38 , the following description will cover both valves and magnetic field generating assemblies. First and second inlet valves  16 ,  38  each  20  includes a valve body  44  including integral pin element  46  extending from valve body  44 . Pin element  46  includes a tip portion  48  positioned at an outer distal end for positioning within the respective inlet  28 ,  32  when the respective valve is in a closed position. Magnetic field generating assemblies  18  and  42  each include a coil  50  mounted on the valve body  44  and positioned around pin element  46 . Coil  50  is connected to an electrical source (not shown) via electrical leads  52 . Magnetic field generating assemblies  18  and  42  also include a non-magnetic sleeve  54  securely mounted on pin element  46  adjacent tip portion  48  for engaging a corresponding valve recess  56  formed in charging body  14 . Nonmagnetic sleeve  54  is formed of a nonmagnetic material, such as stainless steel. As best shown in FIG. 1 c,  various O-ring grooves and complementary O-rings  58  may be formed in and positioned on the outer surface of nonmagnetic sleeve  54  to form an effective seal against the inner wall of valve recess  56  when first and second inlet valves  16  and  38  are in the closed position. 
     Magnetic field generating assemblies  18  and  42  effectively generate a magnetic field or flux which minimizes unwanted leakage during operation in the following manner. First, it should be noted that pin element  46 , charging body  14  and valve blocks  36 ,  40  are all formed of magnetic material. When first and second inlet valves  16 ,  38  are in the closed position as shown in FIG. 1 b,  electrical current may be supplied to coil  50  via leads  52 . Upon energization of coil  50 , a magnetic field is generated in a pattern as shown in FIG. 1 c  as magnetic flux is channeled by nonmagnetic sleeve  54  through pin element  46 . With specific reference to FIG. 4 a,  the magnetic lines of flux specifically extend from tip portion  48  of pin clement  46  across an inherent annular clearance gap  60  (FIG. 4 b ) formed between tip portion  48  and the surrounding wall forming first and second inlets  28 ,  32  into charging body  14 . As a result, magnetorheological fluid present in clearance gap  60  experiences a magnetorheological effect sufficient to prevent leakage flow through, and MR fluid flow from, clearance gap  60 . This stabilization of MR fluid in clearance gap  60  thereby prevents the MR fluid in clearance gap  60  from flowing into bore  20 . The MR effect experienced by the MR fluid in clearance gap  60  prevents clearance gap  60  from functioning as a drain passage permitting flow around an outer seal  62 , i.e. O-ring, positioned on the outer surface of seal cover assembly  26 . 
     A better understanding of the advantage of the present charging system in minimizing undesirable leakage will best be understood in conjunction with a description of the operation of charging system  10 . As shown in FIG. 1 b,  first and second inlet valves  16  and  38  are initially in a closed position blocking fluid flow through the respective inlets. Damper cylinder  12  is connected to one end of charging body  14  while gas cup  24 , damper piston  22  and seal cover assembly  26  are moved into position within bore  20 . Gas cup  24  is positioned in bore  20  between first inlet  28  and second inlet  32  while damper piston  22  is also positioned between first and second inlets  28 ,  32  to the right of gas cup  24  as shown in FIG. 1 b . Referring to FIG. 2, at a preselected moment, first and second inlet valves  16 ,  38  are moved into an open position to permit MR fluid flow from fluid supply circuit  30  through first inlet  28  into chamber  66  and gas from gas supply circuit  34  to flow through second inlet  32  into a gas chamber  68  to the left of gas cup  24 . During this filling operation, MR fluid flows from chamber  66  through conventional passages  70  formed in damper piston  22  into chamber  64  thereby filling both chambers  66  and  64 . Once the chambers are full, first and second inlet valves  16 ,  38  are moved back into the closed position as shown in FIG. 1 b  blocking MR fluid and gas flow into the respective chambers. A press member  72 , which may have been previously used to insert each damper component into bore  20 , is then moved to the left in bore  20  as shown in FIG. 3 so as to displace seal cover assembly  26 , damper piston  22  and gas cup  24  toward damper cylinder  12 . During this pressing operation, seal cover assembly  26  necessarily moves past both first inlet  28  and second inlet  32 , for example, as shown in FIG. 3 with respect to second inlet  32 . During this movement, seal  62 , positioned on seal cover assembly  26 , will reach the position shown in FIG. 4 a,  with respect to both first inlet  28  and second inlet  32 . As shown in FIG. 4 a,  clearance gap  60 , formed between tip portion  48  and the wall of charging body  14  forming the respective inlet, communicates with a first cover clearance gap  74  formed on one side of seal  62  and a second cover clearance gap  76  extending from an opposite side of seal  62 . As a result, in conventional systems, when seal cover assembly  26  is in the position shown in FIG. 4 a  relative to both first inlet  28  and second inlet  32 , a fluid flow path is created which disadvantageously causes MR fluid flow from MR fluid chamber  66  through cover clearance gap  74 , clearance gap  60  and cover clearance gap  76  into an outer chamber  78 . This leakage flow of MR fluid into outer chamber  78  creates a waste quantity of MR fluid, more difficult cleanup and thus increased cost since chamber  78  is open to the surrounding environment. The system and method of the present invention solves this leakage problem by energizing magnetic field generating assemblies  18  and  42  upon first inlet valve  16  and second inlet valve  38  being moved into the closed position after filling is complete and before pressing the components inwardly from the position shown in FIG. 1 b.  The magnetorheological effect experienced by the MR fluid in clearance gap  60  of both first inlet  28  and second inlet  32  causes the MR fluid to increase in viscosity sufficiently to block fluid flow through clearance gap  60 . Accordingly, MR fluid leakage between chamber  66  and outer chamber  78  via clearance gap  60  is substantially eliminated. Also, after seal cover assembly  26  moves completely past first inlet  28 , magnetic flow generating assembly  18  remains energized so as to prevent leakage of MR fluid in clearance gap  60  from draining into outer chamber  78  both before and after the removal of press member  72  which occurs after completely displacing the components and fluid into damper cylinder  12 . Likewise, magnetic field generating assembly  42  preferably remains energized after seal cover assembly  26  passes second inlet  32  to prevent leakage of MR fluid in clearance  60  which entered clearance  60  as chambers  64  and  66  passed over clearance  60 . 
     In summary, the MR damper charging system  10  of the present invention effectively substantially minimizes MR fluid leakage during the MR damper assembly process thereby reducing costs associated with MR fluid consumption and MR fluid cleanup while avoiding environmental challenges associated with magnetorheological fluid spillage. In addition, the present MR damper charging system effectively eliminates the undesirable leakage of MR fluid into gas chamber  68  which is also undesirable.