Abstract:
A system and method for self-powered magnetorheological-fluid damping of mechanical vibrations includes a hydraulic cylinder. The hydraulic cylinder is configured for at least partially disposing magnetorheological fluid therein. A piston head is disposed within the hydraulic cylinder. The piston head has first and second sides and is configured to be in sliding engagement with the hydraulic cylinder. A piston rod is at least partially disposed within the hydraulic cylinder and is connected to the piston head on the first side. The system also includes a vibration absorber assembly having housing. The vibration absorber assembly is configured to transduce mechanical vibrations of the piston rod to electric current.

Description:
PRIORITY CLAIM TO PROVISIONAL APPLICATION 
       [0001]    This patent application claims priority to and the benefit of U.S. Provisional Patent Application No. 60/824,141, filed in the U.S. Patent and Trademark Office on Aug. 31, 2006, entitled “Self-Powered Magnetorheological Dampers”. 
     
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to magnetorheological-fluid damping, and, in particular, to a system and method for self-powered magnetorheological-fluid damping of mechanical vibrations. 
         [0004]    2. Description of Related Art 
         [0005]    Generally, magnetorheological fluids (herein referred to as “MR” fluids) are a class of fluids that change in viscosity in the present of a magnetic field. An MR fluid may have the viscosity of commercially available motor oil when no magnetic field is present and may behave similarly to a solid when a magnetic field is applied (e.g., it may become a viscoelastic solid). Therefore, they exhibit controllable yield strength. When no magnetic field is present, MR fluids may be sufficiently modeled as Newtonian liquids. These unique properties make the material ideal for mechanical vibration damping because of the ability to utilize a magnetic field to control the apparent viscosity of an MR fluid. Additionally, an MR fluid may have a response time of less than 10 milliseconds making it well suited for mechanical vibration damping systems. 
         [0006]    MR fluid dampers are emerging as a promising technology for semi-active actuator damping. They have been widely applied to control and suppress unwanted mechanical vibrations and shock of various systems and structures because of their inherent advantages. Such advantages include its ability to assist in continuously controlling force, its fast response, and its relatively small power consumption. Some mechanical vibration and shock mitigation systems that utilize MR fluid dampers include either a power supply and/or a current amplifier. Electrical current is inevitably necessary for activating electromagnetic coils (e.g., a stator) inside MR fluid dampers for providing a controllable magnetic field to affect the MR fluid. However, there has been a continuing need to reduce the electrical energy needed (e.g., electric current), to reduce the weight of the system, and to reduce the maintenance needed in any damping system including MR-fluid damping systems. Additionally, there has been a continuing need to the maintain cost-effectiveness of MR-fluid damping systems. 
       SUMMARY 
       [0007]    The present disclosure relates to magnetorheological-fluid damping, and, in particular, to a system and method for self-powered magnetorheological-fluid damping of mechanical vibrations. 
         [0008]    In one aspect thereof, a magnetorheological-fluid damping system includes a hydraulic cylinder configured for at least partially disposing magnetorheological fluid therein. A piston head is disposed within the hydraulic cylinder and has first and second sides. The piston head is configured to be in sliding engagement with the hydraulic cylinder. A piston rod is at least partially disposed within the hydraulic cylinder and is connected to the piston head on the first side. The system also includes a vibration absorber assembly having a housing. The vibration absorber assembly is configured to transduce mechanical vibrations of the piston rod to electric current. A current amplifier may amplify the electric current transduced by the vibration absorber assembly. The vibration absorber assembly may be attached to the first side of the piston head, the hydraulic cylinder, or the piston rod. 
         [0009]    The piston head may include a coil winding configured to convert the electric current to a magnetic field to affect the magnetorheological fluid. A floating piston may be disposed in the hydraulic cylinder forming a magnetorheological fluid chamber and a gas chamber. The floating piston is configured to maintain a predetermined pressure range of the pressure of the magnetorheological fluid as the piston rod slides through the hydraulic cylinder. 
         [0010]    The magnetorheological-fluid damping system may be an installable module installable in an engine mount. Additionally or alternatively, the system may be utilized to dampen an engine and the vibration absorber assembly may have a predetermined resonance frequency from about 0 Hertz to about 100 Hertz. 
         [0011]    In another aspect thereof, the vibration absorber assembly may be attached to the hydraulic cylinder and may include a magnet disposed within the housing. The magnet may be attached to the piston rod. The vibration absorber assembly may include a stator configured to receive the magnetic field of the magnet to transduce the mechanical vibrations of the piston rod to the electric current. 
         [0012]    In another aspect thereof, the vibration absorber assembly may include a magnet, a stator and a spring. The magnet may form a hole and may be in sliding engagement with the piston rod. The piston rod may be positioned through the hole of the magnet. The stator may receive the magnetic field of the magnet to transduce to the mechanical vibrations of the piston rod to the electric current. Additionally or alternatively, the stator may be configured for receiving a changing magnetic field inducing the electric current. The spring includes first and second attachment points. The first attachment point may be attached to the housing and the second attachment point may be attached to the magnet. 
         [0013]    In another aspect thereof, a method for dampening mechanical vibrations utilizing magnetorheological fluid is disclosed. The method includes providing a magnetorheological-fluid damping system, such as at least one of the systems mentioned supra, and dampening the mechanical vibrations. The mechanical vibrations may include at least one frequency constituent. Each frequency constituent has frequency and amplitude. Furthermore, the step of dampening the mechanical vibrations may include dampening a resonance frequency of an engine. Additionally or alternatively, the piston head may include a coil winding configured to convert the electric current to a magnetic field; the magnetic field being configured to affect the magnetorheological fluid. And the method may further include injecting the electric current into a coil winding. 
         [0014]    In another aspect thereof, a magnetorheological-fluid damping system is disclosed including a means for utilizing magnetorheological fluid to dampen the movement of a piston head; the piston head is disposed with a hydraulic cylinder. The system includes a means for transducing mechanical vibrations to electric current within the hydraulic cylinder and a means for converting the electric current to a magnetic field. The magnetic field is configured to affect the magnetorheological fluid. The means for transducing mechanical vibrations to the electric current within the hydraulic cylinder may include a means for providing a changing magnetic field through a stator. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    These and other advantages will become more apparent from the following detailed description of the various embodiments of the present disclosure with reference to the drawings wherein: 
           [0016]      FIG. 1  is a schematic drawing of a cross-section view of an MR fluid damping system having a vibration absorber assembly attached to a piston head with a magnet in sliding engagement with a piston rod in accordance with the present disclosure; 
           [0017]      FIG. 2  is a schematic drawing of a cross-section view of an MR fluid damping system having a vibration absorber assembly attached to a piston rod with a magnet in sliding engagement with the piston rod in accordance with the present disclosure; 
           [0018]      FIG. 3  is a schematic drawing of a cross-section view of an MR fluid damping system having a vibration absorber assembly attached to a hydraulic cylinder with a magnet attached to a piston rod in accordance with the present disclosure; 
           [0019]      FIG. 4  is a schematic drawing of an engine mounting system utilizing an MR fluid damping system to dampen an engine mass in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Referring to the drawings, simultaneously refer to  FIGS. 1 ,  2 , and  3  which depict a schematic diagram of an MR fluid damping system  100 . MR fluid damping system  100  may be used to dampen engines, used in an engine mount, protect equipment, and/or may be used to dampen any other device from mechanical vibrations. For example, MR fluid damping system  100  may be used in a car to dampen the engine from the frame. Additionally or alternatively, MR fluid damping system  100  may be used in automobile “shocks” to dampen the mechanical vibrations coming from the tires to the passengers. 
         [0021]    MR fluid damping system  100  may include a hydraulic cylinder  102  that houses fluid, e.g., MR fluid, air, oil, and/or other material, liquids or components. MR fluid system  100  may also include piston rod  104  in sliding in sliding engagement with hydraulic cylinder  102 . The term “sliding engagement” is not intended to engagements in which the two items are touching, e.g., piston rod  104  may utilize one or more bearings so that piston rod  104  may slide in and out of hydraulic cylinder  102 . Additionally or alternatively, bushings, bearings, rings, sealers, lubricants, gaskets and/or other technologies may be utilized in the sliding engagement of piston rod  104  with hydraulic cylinder  102 . 
         [0022]    Additionally, MR fluid damping system  100  may include floating piston  106 . Floating piston  106  may divide hydraulic cylinder  102  into MR fluid chamber  108  and gas chamber  110 . MR fluid chamber  108  may be wholly or partially filled with MR fluid, while gas chamber  110  may be wholly or partially filled with gas. Additionally or alternatively, a gasket and/or an O-ring may be positioned relative to floating piston  106  to prevent leakage between MR fluid chamber  108  and gas chamber  110 . 
         [0023]    Floating piston  106  may be configured such that a predetermined pressure range of the MR fluid chamber  108  is maintained for adequate operation of MR fluid damping system  100 . For example, consider piston rod  104  moving out of hydraulic cylinder  102  reducing the aggregate volume of MR fluid chamber  108 ; this may cause the MR fluid to drop in pressure creating a “back pressure” impeding the outward movement of piston rod  104 . Floating piston  106 , in this example, may move toward MR fluid chamber  108  reducing the volume of MR fluid chamber  108  while increasing the volume of gas chamber  110 , thus alleviating the “back pressure”. Floating piston  106  may operate reverse to the above example when piston rode  104  moves into hydraulic cylinder  102 . 
         [0024]    MR fluid damping system  100  may have piston rod  104  connected to piston head  112  as indicated by a circle approximating the general location of piston head  112  as shown in  FIGS. 1 ,  2 , and  3 . Piston head  112  may have coil winding  114 . Coil winding  114  may be configured to create a magnetic field (not depicted) that affects the magnetorheological fluid. For example, in the situation where coil winding  114  creates no magnetic field (or minimal magnetic field), the MR fluid surrounding piston head  112  may behave as if the it were surrounded by a low viscosity liquid, allowing piston head  112  and piston rod  104  to move up and down with little resistance. However, note that as the apparent viscosity of the fluid increases the more “damped” the movement of head  112  (thus piston rod  104 ) becomes because of the difficulty the MR fluid has to move around piston head  112 . Therefore, by increasing the magnetic field created by coil winding  114 , the MR fluid becomes more viscous resulting in a more “damped” movement of piston head  112  when moving throughout hydraulic cylinder  102 . Thus, by utilizing coil winding  114  to control a magnetic field configured to affect the MR fluid, it is possible to control the damping of MR fluid damping system  100 . Coil winding  114  may create the magnetic field by running an electric current through the wires. The relationship between electricity and magnetism is well known. 
         [0025]    Coil winding  114  may form a solenoid configuration and also may utilize a “soft” ferromagnetic material to enhance and/or shape the magnetic field. Also, a permanent magnet (not shown), such as a rare earth magnet, may be positioned to increase the magnetic field acting of the MR fluid. Additionally or alternatively, the relevant active poles may be positioned anywhere to suitably affect the MR fluid; however, actives poles  116  are depicted. 
         [0026]    The electric current that activates coil winding  114  may be generated and/or created by vibration absorber assembly  118  (herein referred to as “VAA  118 ”). VAA  118  may include magnet  120  disposed inside housing  122 . Housing  122  may prevent fluid (e.g., MR fluid) and/or gas from entering into VAA  118 . Additionally or alternatively, housing  122  may prevent fluid (e.g., oil) and/or air from escaping from within VAA  118 . Magnet  120  may be circular and may form a hole. Piston rod  104  may be positioned within that hole. Note that in  FIGS. 1 and 2 , magnet  120  is in sliding engagement with piston rode  104 , while in  FIG. 3  it is attached to piston rod  104 . 
         [0027]    Magnet  120  may be attached to housing  122  via spring  124 . As mechanical vibrations reach VAA  118  magnet  120  may freely move up and down relative to piston head  112 . Additionally, in the embodiments depicted in  FIGS. 1 and 2 , magnet  120  may move up and down relative to piston rod  104 . However, in  FIG. 3 , magnet  120  is attached to piston rod  104 , thus moving with piston rod  104 , while housing  122  remains stationary relative to hydraulic cylinder  102 . However, some of Equations 1 through 11b may not apply to  FIG. 3  because the movement of magnet  120  follows piston rod  104 . Regardless of the embodiment, magnet  120  is configured within VAA  118  to move relative to stator  126 . 
         [0028]    The magnetic field of magnet  120  may sweep across stator  126  when magnet  120  moves inducing electric current. This arrangement may cause VAA  118  to transduce mechanical vibrations to electric current. The term “transduce” is defined herein as “converting one form of energy to another”, the verb “transducing” is the act of “converting one form of energy to another”, and the term transduced is an adjective used to refer to “a form of energy that has been converted from one form of energy to the present form”. The mechanical vibrations may come from piston rod  104  and/or from hydraulic cylinder  102 . This electric current generated by VAA  118  may be used to generate a magnetic field via utilizing coil winding  114 . This may be accomplished by connecting the positive and negative terminals of stator  126  to the positive and negative terminals of coil winding  114  (terminals not shown). Additionally or alternatively, VAA  118  may be “tuned” to absorb different mechanical vibrations according to its frequency, polarization, and/or direct of travel. 
         [0029]    In the embodiments shown in  FIGS. 1 and 2 , magnet  120  may show relative motion to piston head  112  and piston rod  104 . The movement of magnet  120  due to piston rod  104  may generate electromotive force (referred to herein as “emf”) in stator  126  and the strength of the emf is proportional to the motion speed of magnet  120 . The emf (induced voltage or current) may be directly provided to activate coil winding  114  in piston head  112  so as to produce a magnetic field into the MR fluid inside hydraulic cylinder  102 . Additionally or alternatively, VAA  118  may itself operate as a mechanical vibration absorber since it is similar to a single degree of freedom mass-spring-damping system. If the resonance frequency of the VAA  118  is matched to that of a target system to be damped (e.g., engine mass  402  in  FIG. 4 , discussed infra), the movement of magnet  120  will be greatly larger than the input excitation motion. 
         [0030]    The emf value of E emf , that is generated by the motion of magnet  120  in VAA  118  is given by Equation (1) as: 
         [0000]    
       
         
           
             
               
                 
                   
                     E 
                     emf 
                   
                   = 
                   
                     
                       
                         - 
                         
                           N 
                           m 
                         
                       
                        
                       
                         
                            
                           Φ 
                         
                         
                            
                           t 
                         
                       
                     
                     = 
                     
                       
                         - 
                         
                           N 
                           m 
                         
                       
                        
                       α 
                        
                       
                           
                       
                        
                       
                         B 
                         m 
                       
                        
                       2 
                        
                       π 
                        
                       
                           
                       
                        
                       
                         
                           r 
                           m 
                         
                         ( 
                         
                           
                             z 
                             * 
                           
                           - 
                           
                             x 
                             * 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0031]    Here, N m  is the turn number of the coil in stator  126  affected by magnet  120  at a time, Φ is the magnetic flux, B m  is the magnetic density of the magnet  120 , r m  is the radius of the magnet  120 , {dot over (x)} is the velocity of piston rod  104 , and ż is the velocity of magnet  120 . α is the empirical correction factor for the effective magnetic density of magnet  120  since there is a gap clearance between magnet  120  and stator  126 . For example, the values may be as follows: N m =120 turns, α=0.75, B m =1.2T, and r m =15 mm. The current I of coil winding  114  due to the emf is given by Equation (2) as follows: 
         [0000]    
       
         
           
             
               
                 
                   I 
                   = 
                   
                     
                       E 
                       emf 
                     
                     
                       
                         R 
                         s 
                       
                       + 
                       
                         R 
                         c 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0032]    Here, R s  is the resistance of stator  126  and R c  is the resistance of coil winding  114 , for example: R s +R c =3Ω. The forces associated with MR fluid damping system  100  may be given by Equation (3) as follows: 
         [0000]        F   d   =F   passive   +F   semi   +F   gas   (3) 
         [0000]      where 
         [0000]                      F   passive     =           A   p   2          (         6      η                 L       π                   rd   3         +       6      η                   L   c         π                   r   c          d   c   3         +       6      η                   L   s         π                   r   s          d   s   3           )            (       x   *     -     y   *       )       +       (         2      ηπ                 rL     d     +       2      ηπ                   r   c          L   c         d   c       +       2      ηπ                   r   s          L   s         d   s         )          (       x   *     -     y   *       )           ,           (   4   )                   F   semi     =       (       2        A   p          L   d       +     2      π                 rL       )            τ   y          (   H   )            sgn   (       x   *     -     y   *       )         ,           (   5   )               and 
         [0000]        F   gas   =K   gas ( x−y )  (6) 
         [0033]    Here, A p  is the effective piston area of piston head  112 , A r  is the area of piston rod  104 , and y is the displacement of hydraulic cylinder  102 . d, d c , and d s  are the gap of active pole  116 , coil winding  114 , and stator  126 , respectively. r, r c , and r s  are the radius of active pole  116 , coil winding  114 , and stator  126 , respectively. L, L c , and L s  are the length of active pole  116 , coil winding  114 , and stator  126 , respectively. η is the fluid viscosity of the MR fluid within hydraulic cylinder  102 , and τ y (H) is the yield shear stress of an MR fluid and is assumed to be a function of the magnetic field strength H as illustrated in the following equations: 
         [0000]      τ y ( H )=0.93 H   1.73 [Pa]  (7) 
         [0000]      where 
         [0000]    
       
         
           
             
               
                 
                   H 
                   = 
                   
                     
                       
                          
                         
                           
                             
                               N 
                               c 
                             
                              
                             I 
                           
                           
                             2 
                              
                             d 
                           
                         
                          
                       
                        
                       
                           
                       
                       [ 
                       
                         A 
                          
                         
                           / 
                         
                          
                         mm 
                       
                       ] 
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
         [0034]    N c  is the turn number of coil winding  114  in piston head  112 . K gas  is the stiffness due to the gas pressure in gas chamber  110  and is given by Equation (9) as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     K 
                     gas 
                   
                   = 
                   
                     
                       
                         
                           nA 
                           r 
                           2 
                         
                          
                         
                           P 
                           0 
                         
                       
                       
                         V 
                         0 
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
         [0035]    n is the specific heat ratio of the gas in gas chamber  110 , and P 0  and V 0  are the initial pressure and volume of gas chamber  110 , respectively. For example, consider the following: A p =1700 mm 2 , A r =79 mm 2 , L=20 mm, L c =15 mm, L s =30 mm, r=24 mm, r c =21 mm, r s =21 mm, d=1 mm, d c =4 mm, d s =4 mm, η=0.18 Pa·s, and N c =150 
         [0036]    To model and/or predicts differing force responses of MR fluid damping system  100 , consider a time response of the semi-active damper force, F semi  as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         F 
                         * 
                       
                       semi 
                     
                     * 
                   
                   = 
                   
                     
                       
                         
                           - 
                           
                             F 
                             semi 
                             * 
                           
                         
                         + 
                         
                           F 
                           semi 
                         
                       
                       τ 
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
         [0037]    Here, F* semi  is an emulated semi-active damper force and r is the time response of MR fluid damping system  100 . In this example, it was chosen to be τ=5 msec. For example, during a computer simulation, the semi-active damper force, F semi  will be replaced by an emulated semi-active damper force, F* semi . 
         [0038]    Referring now to the drawings,  FIG. 4  depicts an engine mounting system  400  that includes an engine mass  402 , engine mass  402  may be a mass created by an engine, and/or any other source of mechanical vibrations and/or mass. Additionally MR fluid damping system  100  is shown as supporting engine mass  402  with coil spring  404 . Piston rod  104  is shown as connecting MR fluid damping system  100  to engine mass  402 . Coil spring  404  may provide force on engine mass  402 , e.g., to help support the weight of engine mass  402 . 
         [0039]    The governing equation of motion for engine mounting system  400  using MR fluid damping system  100  is illustrated by Equations (11a) and (11b) as follows: 
         [0000]                        M   s            x   **     s       =         -     (       K   s     +     K   gas       )            (       x   s     -     x   e       )       -     F   passive     -     F   semi   *     +       K   a          (       x   a     -     x   s       )       +       C   a     (         x   *     a     -       x   *     s       )     +     F   ext         ,           (     11      a     )               and 
         [0000]        M   a   {umlaut over (x)}   a   =K   a ( x   a   −x   s )− C   a   ({dot over (x)}   a   −{dot over (x)}   s )  (11b) 
         [0040]    M s  is the mass of engine mass  402 , M a  is the mass of magnet  120  in MR fluid damping system  100 , F ext  is the external shock force, K s  is the stiffness of the coil spring  404 , K a  and C a  are the stiffness and the damping of spring  124  in MR fluid damping system  100 , respectively. x s  is the displacement of the engine mass  402 , x a  is the displacement of magnet  120 , and x e  is the excitation displacement. For example, the values may be as follows: M s =60 kg, M a =0.4 kg, K s +K gas =150 kN/m, and C a =4 N·s/m. 
         [0041]    In some environments, the vibration isolation performance of a vibration isolation system is designed so that there is higher damping around a resonance frequency and lower damping above the resonance frequency. In these environments, an MR fluid damping system  100  may be turned “on” around the resonance frequency and turned “off” above the resonance frequency to provide effective performance. However, VAA  118  may be analogized and/or modeled as a “spring-mass” system having a resonance frequency; thus, spring  124  of VAA  118  may have larger displacements around the “resonance frequency” of VAA  118 . Frequencies higher than the resonance frequency of VAA  118  causes the displacements of magnet  120  to become smaller than the displacements experienced around the resonance frequency. This behavior causes MR fluid damping system  100  to produce high damping around the resonance frequency of VAA  118  and low damping above the resonance frequency of VAA  118 . Note that MR fluid damping system  100  does not utilize any sensors, microprocessors, control inputs, and/or control algorithms; however, it is envisioned that one of ordinary skill in the relevant art will appreciate their use in appropriate applications and/or environments. 
         [0042]    Referring again to  FIG. 4 , an example resonance frequency of engine mounting system  400  may be 8.0 Hz; therefore, an initial choice for the stiffness of VAA  118  is theorized to be K a =1000 N/m to match the resonance frequency of VAA  118  with that of engine mounting system  400 . However, in order to find an optimal stiffness, the maximum peak value of the transmissibility, |x s /x e |, of the engine mounting system vs. the stiffness of VAA  118  in MR fluid damping system  100  may be calculated. From this calculation, the optimal stiffness value of VAA  118  for engine mounting system  400  is K a =700 N/m. This optimal stiffness, K a =700 N/m, utilizes a resonance frequency of VAA  118  slightly lower than that of the engine mounting system  400 . The optimal stiffness, K a =700 N/m, of VAA  118  for engine mounting system  400  may be used to evaluate the vibration isolation capability of MR fluid damping system  100 . 
         [0043]    Accordingly, it will be understood that various modifications may be made to the embodiments disclosed herein, and that the above descriptions should not be construed as limiting, but merely as illustrative of preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.