Abstract:
A magnetorheological damper device is provided having a high-bandwidth and high-control ratio, which enhances the performance of the damper. The damper generally includes a cylindrically shaped housing; a magnetorheological fluid disposed in the cylindrically shaped housing; a piston assembly disposed within the cylindrically shaped housing in sliding engagement with the cylindrically shaped housing defining a first chamber. The first chamber is in communication with a second chamber, through a magnetorheological valve assembly which comprises of a plurality of cylindrically shaped fluid passageways extending from the first chamber to the second chamber, and an electromagnet; and a power supply in electrical communication with the electromagnet.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/471,932 filed Jun. 21, 2006 entitled Magnetorheological Damper With Annular Valve (as amended), which claims priority to U.S. Provisional Application Ser. No. 60/692,449 filed Jun. 21, 2005 entitled Linear Magnetorheological Damper With Fixed Annular Valve and to U.S. Provisional Patent Application Serial No. 60/762,334 filed Jun. 25, 2005 entitled Reduced Height Linear Magnetorheological Damper With Integrated Gas Spring, both of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention generally relates to linear vibration dampers. More specifically, the present invention relates to a linear vibration damper utilizing a magnetorheological (MR) fluid. 
         [0003]    Conventional linear vibration dampers include MR dampers having a cylinder containing MR fluid and a piston which slidably engages the cylinder. The MR fluid passes though an orifice on the piston. Exposing the MR fluid in the orifice to a magnetic field generated by an electrical coil located within the piston causes a change in the shear strength of the fluid flowing through the orifice, providing variable damping of relative motion between the piston and cylinder. The damping force is controllable by varying the strength of the magnetic field generated by the piston coil. To improve the control ratio (the damping force created by a fully energized coil divided by the damping force of a de-energized coil) of the damper, many MR damper pistons utilize an annular orifice. The width of the annular orifice in these devices must be precisely maintained to provide a predictable, repeatable change in damping force when a current is applied to the coil. Also, a magnetic flux return path outside of the fluid flow path is necessary to achieve a higher control ratio. Often in these devices, a compromise must be made between maximizing the flow area of the annular orifice (producing a higher control ratio) and the need to provide a durable bearing surface on the exterior of the piston (providing a longer damper service life). If this bearing surface is constructed from a magnetically-permeable material, it can also serve as the flux return path, but at the expense of reduced annular flow area and a corresponding reduction in control ratio. 
         [0004]    It is also desirable to incorporate a gas spring into the vibration damper. Properly integrated, the gas spring can serve several purposes. It can prevent cavitation of the MR fluid by eliminating low pressure regions during damper compression and extension. When utilized as part of the suspension of a ground vehicle, the gas springs can be connected to a reservoir of high pressure gas through controllable valves and used to adjust the ride height of a vehicle to compensate for changing payloads as well as supporting the vehicle&#39;s sprung mass. 
         [0005]    Therefore, a need exists for a damper with a very high control ratio, an integrated gas spring, and a relatively long service life. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0006]    One object of the present invention is to provide a high-bandwidth adjustable vibration damping between two components of a system experiencing relative motion. Such systems include but are not limited to: the suspension systems of ground vehicles which operate on smooth roads, the suspension systems of ground vehicles which operate on roads and also in rough terrain, the steering systems of ground vehicles, aircraft landing gear, washing machine drum vibration control systems, shock load attenuating devices, and impact load attenuating devices. It will be apparent to those skilled in the art that a system in accordance with the present invention can be used in virtually any application where a conventional passive damper is used, regardless of the construction of the passive damper. 
         [0007]    In one aspect of the present invention, the damper system utilizes a fixed annular valve instead of a piston-mounted valve, thereby separating the function of fluid sealing from the function of damping force generation. This allows the annular valve area to be maximized while also maintaining a precise distance between the flux core and the flux return path. In this regard, a large flowpath diameter is one that is larger than the piston head diameter, or, in the case of preferred embodiment two, larger than the internal concentric tube. Thus, for the same off-state pressure drop across the valve, the flowpath gap (defined as the Outer Radius of the flowpath minus the Inner Radius of the flowpath) can be narrower and achieve a higher on-state pressure drop, which means a higher control ratio. 
         [0008]    In another aspect of the present invention, a damper system incorporates a gas spring in fluid communication with the MR fluid chamber to prevent cavitation of the MR fluid and also to serve as a steady-state support for the vehicle. Such a gas spring may be of the fixed spring rate, sealed chamber type or it may also be in fluid communication with a pneumatic reservoir to provide adjustable vehicle ride height (adjustable spring preload) or adjustable spring rate. 
         [0009]    In another aspect of the present invention, an annular valve includes of a flux core made of one or more stacked coils which can be energized independently or simultaneously by a control system. One such control system that could be used is the control system disclosed in U.S. Pat. No. 6,953,108 entitled Magnetorheological Damper System, the contents of which are hereby incorporated by reference. Such a control system can include a routine for energizing one or more of said coils in response to at least one sensed condition of said damper so as to dampen forces exerted on said damper. 
         [0010]    There are several preferred embodiments for this invention. A first, henceforth referred to as Preferred Embodiment One, minimizes overall damper length as well as providing the highest control ratio and low pressure losses throughout the fluid path. Another preferred embodiment, henceforth referred to as Preferred Embodiment Two, is less linearly compact as Preferred Embodiment One, but is lighter, less complex, and more efficiently manufactured. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  is a cross-sectional view of a first preferred embodiment of an MR damper in accordance with the present invention. 
           [0013]      FIG. 2  is a detail view of  FIG. 1 . 
           [0014]      FIG. 3  is an additional cross-sectional view of the MR damper of  FIG. 1 . 
           [0015]      FIG. 4  is a detail view of  FIG. 3  showing the fluid flow direction during a compression stroke. 
           [0016]      FIG. 5  is a cross-sectional view of a second preferred embodiment of a MR damper in accordance with the present invention. 
           [0017]      FIG. 5A  is a detail view of  FIG. 5 . 
           [0018]      FIG. 6  is a cross-sectional view of the annular valve assembly of  FIG. 5 . 
           [0019]      FIG. 7  is a cross-sectional view of a third preferred embodiment of an MR damper in accordance with the present invention. 
           [0020]      FIG. 7A  is a detail view of  FIG. 7 . 
           [0021]      FIG. 8  is a cross-sectional view of a fourth preferred embodiment of a MR damper in accordance with the present invention. 
           [0022]      FIG. 8A  is a detail view of  FIG. 8 . 
           [0023]      FIG. 9  is a prior art twin-tube damper shown in the extended and retracted positions. 
           [0024]      FIG. 10  illustrates a damping control ratio. 
           [0025]      FIG. 11  illustrates a damping control ratio. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Discussed below is a detailed description of several preferred embodiments of the present invention. This detailed description is not meant to be limiting but rather to illustrate the general principles of the present invention. Departures may be made from such details without departing from the scope or spirit of the general inventive concept. Those skilled in the art will appreciate that the principles constituting the invention can be applied with great success to any number of applications that require management of shock and vibration forces. 
       Prior Art Damper 
       [0027]      FIG. 9  depicts a cross-sectional view of a prior art conventional twin-tube vibration damper  410  consisting of inner cylinder  412  and outer cylinder  414  which are in fluid communication through fluid ports  416 . During the compression stroke of vibration damper  410 , hydraulic fluid flows from lower fluid chamber  418  of inner cylinder  412  through orifice  419  and into upper fluid chamber  420  while piston  422  descends, increasing the volume of piston rod  424  which is immersed in hydraulic fluid. To compensate for this increased rod volume, gas  426  is compressed, occupying a smaller volume within outer cylinder  414 . For the extension stroke of vibration damper  410 , the flow is reversed through orifice  419  as piston  422  ascends and a decreased volume of piston rod  424  is immersed in hydraulic fluid. To compensate for this decreased rod volume, gas  426  expands, occupying a larger volume within outer cylinder  414 . 
       Preferred Embodiment One 
       [0028]      FIG. 1  depicts a cross-sectional view of Preferred Embodiment One of a vibration damper  10 , in accordance with various aspects of the present invention, having an outer housing assembly  12  and an inner cylinder tube piston assembly  14 . Integrated into the center of the outer housing assembly  12  is annular valve  16  which defines an upper fluid chamber  26  and a lower fluid chamber  18  to contain a magnetorheological (MR) working fluid therein. Since piston assembly  14  is only exposed to fluid on the upper face of piston head  13 , no rod volume compensator gas  426  is necessary in contrast to the prior art damper shown in  FIG. 9 . Since gas  426  is a thermal insulator, vibration damper  10  functions without the excessive heat buildup of vibration damper  410 . Piston assembly  14  can be perforated by at least one pressure equalization hole  15 , allowing fluid communication between inner piston chamber  17  and air chamber  19  to prevent excessive pressure buildup in air chamber  19  as piston assembly  14  moves with respect to outer housing assembly  12 . Pressure buildup may also be prevented by creating at least one vent hole in piston seal flange  21 , allowing fluid communication between air chamber  19  and atmospheric air. Outer housing assembly  12  is further divided by dynamic separator piston  22  which defines a gas chamber  24 . Gas chamber  24  contains a compressible gas, which acts as a spring to prevent cavitation of the MR working fluid in upper chamber  26  and also to provide a steady-state resistance force between two components of a system experiencing relative motion, such as a ground vehicle&#39;s chassis and wheel. At the opposing ends of vibration damper  10  are two clevis eyes  20 , providing attachment points between two components of a system experiencing relative motion, such as a ground vehicle&#39;s chassis and wheel. 
         [0029]    A detail view of annular valve  16  is shown in  FIG. 2  and an additional cross-sectional view of vibration damper  10  is shown in  FIG. 3 .  FIG. 4  is a detailed close up view of  FIG. 3  for clearer understanding of annular flow path  30 . 
         [0030]    During the compression stroke of the vibration damper  10 , fluid leaves lower fluid chamber  18  and enters annular valve inlet  28 . MR fluid flow is efficiently directed into annular valve inlet  28  to annular flow path  30  by center body nosecone  32  and magnetically-permeable inlet side wall  34 , where it is exposed to a variable magnetic field generated by at least one electromagnetic coil  36 . Annular flow path  30  travels down one side of magnetic coil stack  38 , around the bottom and then up between magnetic coil stack  38  and magnetically-permeable outer side wall  48 . If desired, magnetically-permeable outer side wall  50  can be replaced by a magnetically-impermeable outer side wall  52  and a magnetically-permeable sleeve  54  as shown. This exposes the MR fluid to the magnetic flux generated by electromagnetic coils  36  a second time, providing a relatively long magnetic flux-affected flow length with a smaller number of electromagnetic coils  36  than is possible with other embodiments while maintaining a the same high control ratio. By using fewer electromagnetic coils  36  electrical inductance is reduced, thereby increasing the damping response rate without reducing the control ratio. Each electromagnetic coil  36  is wound on bobbin  48  for ease of assembly, positioned on a magnetically-permeable ring  40 , and covered by magnetically-impermeable covers  42  front and back. Each electromagnetic coil  36  is connected to an electrical current source via electrical leads  44  and can be independently energized, allowing precise tailoring of the damping forces generated by vibration damper  10 . In this embodiment, electrical leads  44  are completely isolated from gas chamber  24 , eliminating the need to provide a sealing mechanism to prevent gas from gas chamber  24  from leaking into and being absorbed by the magnetorheological fluid contained in vibration damper  10 . After passing through annular path  30  the MR fluid is efficiently directed through a series of radial ports  46  of annular valve  16  and into upper fluid chamber  26 . Since no gas reservoir is required to compensate for the changing rod volume as in the conventional twin-tube damper shown in  FIG. 9 , heat which is generated in the magnetorheological fluid during the compression and extension of vibration damper  10  is conducted efficiently to outer side wall  52  where it is rejected to atmosphere. To mitigate the effects of an extremely rapid compression of the damper, blow-off valve  56  allows for an increased fluid flow rate between lower fluid chamber  18  and upper fluid chamber  26 . Blow-off valve  56  automatically closes during the rebound stroke of the damper, forcing all fluid flowing between upper fluid chamber  26  and lower fluid chamber  18  to follow annular path  30 . For the rebound stroke of the vibration damper  10  the flow is reversed, starting in upper fluid chamber  26 , proceeding through radial ports  46 , through annular path  30 , out annular valve inlet  28  and into lower fluid chamber  18 . 
       Preferred Embodiment Two 
       [0031]      FIG. 5  and  FIG. 5A  depict a cross-sectional view of Preferred Embodiment Two of a vibration damper  110 , according to various aspects of the present invention, having an outer cylinder tube  112  and an inner cylinder tube  114 . Attached to the lower end of inner cylinder tube  114  is annular valve  116  which defines an upper fluid chamber  126  and a lower fluid chamber  118  to contain a magnetorheological (MR) working fluid therein. Annular chamber  128  exists in the area between outer cylinder tube  112 , inner cylinder tube  114 , and outer cylinder fluid seals  130 . Inner cylinder tube  114  is further divided by dynamic separator piston  122  which defines a gas chamber  124 . Gas chamber  124  contains a compressible fluid or gas, which acts as a spring to prevent cavitation of the MR working fluid in upper chamber  116  and also to provide a steady-state resistance force between two components of a system experiencing relative motion, such as a ground vehicle&#39;s chassis and wheel. Protruding through dynamic separator piston  122  is wiring tunnel  129 , which isolates the wiring for annular valve  116  from the gas in gas chamber  124  and the MR fluid in upper fluid chamber  126 . Using solid core wires through gas path instead of stranded wires aids sealing. An O-ring is used instead of, for example, a crimped ferrule as shown in prior art U.S. Pat. No. 5,878,851, the contents of which is incorporated by reference. More particularly, the referenced prior art patent uses a crimped ferrule around a single wire and a damper body common instead of two wires as in this embodiment. 
         [0032]    At the opposing ends of vibration damper  110  are two clevis eyes  120 , providing attachment points between two components of a system experiencing relative motion, such as a ground vehicle&#39;s chassis and wheel. 
         [0033]    A detail cross-section of annular valve  116  is shown in  FIG. 6 . Fluid enters and exits annular chamber  128  through an array of flow ports  132  spaced around annular valve inlet  134 . Check plate  136  provides a greatly reduced flow rate through flow ports  132  during the rebound stroke of vibration damper  110 . This use of a passive rebound cutoff allows the high control ratio of damper  110  to be employed entirely in the compression stroke of vibration damper  110  as shown in  FIG. 10  instead of being split between the compression stroke and the rebound stroke as in  FIG. 11 . As a result, control ratio can be maximized in the desired region of jounce instead of being spread across both jounce and rebound regions. 
         [0034]    In connection with an example of high control ratios, preferred embodiment one and two will preferably provide a control ratio of approximately 8-12, and more preferably a ratio of about ten 10. Prior art MR dampers typically have a control ratio of 2.0 or 3.0. 
         [0035]    During the compression stroke of vibration damper  110 , fluid leaves lower fluid chamber  118  and enters annular valve inlet  134 . MR fluid flow is efficiently directed around valve centerbody  154  to annular path  138  by centerbody nosecone  140  and inlet sidewall  142 , where it is exposed to a variable magnetic field generated by a one or more electromagnet coils  144 . Each electromagnet coil  144  is wound on a bobbin for ease of assembly, positioned over a magnetically-permeable modular core  146 , and covered by a magnetically-impermeable coil cover  148 . Each electromagnet coil  144  is connected to an electrical current source via electrical leads  150  and is independently energizable, allowing precise tailoring of the damping forces generated by vibration damper  110 . After passing through annular path  138  the MR fluid is efficiently directed through a series of radially-spaced exhaust ports  152  of valve centerbody  154  and into upper fluid chamber  126 . For the rebound stroke of vibration damper  110  the flow is reversed, starting in upper fluid chamber  126 , proceeding through exhaust ports  152 , through annular path  138 , out annular valve inlet  134  and into lower fluid chamber  118 . 
       Preferred Embodiment Three 
       [0036]      FIG. 7  and  FIG. 7A  depict a cross-sectional view of a third preferred embodiment in accordance with aspects of the present invention. This third preferred embodiment has the high control ratio and long service life of previous embodiments, but can be utilized in applications where the overall length of the vibration damper must be minimized. Vibration damper  210  consists of a magnetically-permeable main cylinder  212  which contains a magnetorheological (MR) working fluid therein and secondary cylinder  214  in fluid communication with said main cylinder via flexible hose  216 . Main cylinder  212  contains a concentric inner cylinder  218  held in position with cylinder end cap  220 . Inner cylinder  218  is divided into upper piston chamber  226  and lower piston chamber  222  by piston  224 . At the opposing ends of vibration damper  210  are two clevis eyes  228 , providing attachment points between two components of a system experiencing relative motion, such as a ground vehicle&#39;s chassis and wheel. During the compression stroke of vibration damper  210 , upward motion of piston  224  forces fluid out of upper piston chamber  226 , through rebound cutoff port  230 , through upper flow ports  232  and into upper valve chamber  234 . Said upper valve chamber is in fluid communication with secondary fluid chamber  236 , which is contained within secondary cylinder  214  and separated from compressible gas chamber  238  by secondary piston  240 . Said gas chamber contains a compressible gas which pressurizes the MR fluid, thus preventing cavitation of the MR fluid during compression and rebound of vibration damper  210 . Fluid displaced from main cylinder  212  by intrusion of piston rod  258  into said main cylinder flows into secondary fluid chamber  236 , further compressing the gas contained within gas chamber  238 . 
         [0037]    Fluid leaves upper valve chamber  234  and is efficiently directed into annular valve  242 , where it is exposed to a variable magnetic field generated by a one or more electromagnet coils  244 . Each electromagnet coil  244  is wound on a bobbin for ease of assembly, positioned over a magnetically-permeable modular core  246 , and covered by a magnetically-impermeable coil cover  248 . Each electromagnet coil  244  is connected to an electrical current source via electrical leads  250  and is independently energizable, allowing precise tailoring of the damping forces generated by vibration damper  210 . After passing through annular valve  242  the MR fluid is efficiently directed into lower valve chamber  252 , through lower flow ports  254  and into lower piston chamber  222 . For the rebound stroke of vibration damper  210  the flow is reversed, starting in lower piston chamber  222 , proceeding through lower flow ports  254 , through annular valve  242 , into upper valve chamber  234  and through upper flow ports  232 . During the reversed flow conditions of the rebound stroke rebound cutoff plate  256  covers rebound cutoff port  230 , greatly reducing fluid flow rate through rebound cutoff port  230  and into upper piston chamber  226 . 
       Fourth Preferred Embodiment 
       [0038]      FIG. 8  and  FIG. 8A  depict a cross-sectional view of a fourth preferred embodiment in accordance with aspects of the present invention. This fourth embodiment has the high control ratio and long service life of the preferred embodiment, but can be utilized in applications where the overall length and diameter of the vibration damper must be minimized. Vibration damper  310  consists of; main cylinder  312 , which contains a magnetorheological (MR) working fluid therein; a valve cylinder  314 , which is in fluid communication with said main cylinder via upper flexible hose  316  and lower flexible hose  318 ; and gas cylinder  320 , which is in fluid communication with said valve cylinder via flexible hose  322 . At the opposing ends of main cylinder  312  are two clevis eyes  344 , providing attachment points between two components of a system experiencing relative motion, such as a ground vehicle&#39;s chassis and wheel. Main cylinder  312  is divided into upper piston chamber  324  and lower piston chamber  226  by piston  328 . Valve cylinder  314 , which is constructed from a magnetically-permeable material, is divided into upper valve chamber  330  and lower valve chamber  332  by valve centerbody  334 . Gas cylinder  320  is divided into fluid chamber  336  and gas chamber  338  by secondary piston  340 . Gas chamber  338  contains a compressible gas which pressurizes the MR fluid, thus preventing cavitation of the MR fluid during compression and rebound of vibration damper  310 . Fluid displaced from main cylinder  212  by intrusion of piston rod  242  into said main cylinder flows into fluid chamber  236 , further compressing the gas contained within gas chamber  238 . 
         [0039]    During the compression stroke of vibration damper  310 , upward motion of piston  328  forces fluid out of upper piston chamber  324  and into upper valve chamber  330  via upper flexible hose  316 . MR fluid flow is efficiently directed around valve centerbody  334  to annular path  346  by centerbody nosecone  348 , where it is exposed to a variable magnetic field generated by a one or more electromagnet coils  350 . Each electromagnet coil  350  is wound on a bobbin for ease of assembly, positioned over a magnetically-permeable modular core  352 , and covered by a magnetically-impermeable coil cover  354 . Each electromagnet coil  350  is connected to an electrical current source via electrical leads  356  and is independently energizable, allowing precise tailoring of the damping forces generated by vibration damper  310 . After passing through annular path  346  the MR fluid is efficiently directed through a series of radially-spaced exhaust ports  358  of valve centerbody  334  and into lower fluid chamber  332 . Fluid leaves lower fluid chamber  332  and enters lower piston chamber  326  via lower flexible hose  318 . For the rebound stroke of vibration damper  310  the flow is reversed, starting in lower piston chamber  326 , proceeding through lower flexible hose  318 , into lower fluid chamber  332 , into exhaust ports  358 , through annular path  346  and into upper valve chamber  330 . Fluid then flows into upper piston chamber  324  via upper flexible hose  316 . 
         [0040]    Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.