Abstract:
An energy harvesting shock absorber includes first and second body portions, where the second body portion defines a fluid chamber. A piston located in the fluid chamber divides the fluid chamber into first and second regions. A rod mechanically couples the piston to the first body portion. A coil surrounds at least a portion of the fluid chamber. A ferromagnetic fluid is in the fluid chamber for moving to induce a change in magnetic flux in the coil, to lubricate an inner surface of the fluid chamber, and to damp relative motion between the first and second body portions.

Description:
RELATED APPLICATIONS 
       [0001]    This application is related to U.S. patent application Ser. No. (not yet assigned), Docket No. 1896/3, entitled “CHAOTIC VIBRATION ENERGY HARVESTER AND METHOD FOR CONTROLLING SAME” filed on even date herewith, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The subject matter described herein relates to energy harvesting systems. More particularly, the subject matter described herein relates to an energy harvesting shock absorber and a method for controlling such a shock absorber. 
       BACKGROUND 
       [0003]    Shock absorbers damp vibrations between moving parts by dissipating kinetic energy. For example, automobile shock absorbers typically include a fluid or gas filled chamber that dissipates kinetic energy through fluid friction or compression of a gas. Other than damping vibrations, conventional shock absorbers do not put the kinetic energy to which they are suscepted to beneficial use. 
         [0004]    Vibrational energy harvesting systems harvest energy from vibrational movement by converting kinetic energy into electrical energy. Typical energy harvesting systems include a permanent magnet and a coil. Vibrational movement of the system causes the permanent magnet to move with respect to the coil and induce a current in the coil. The induced current can be used to power an external system, such as a sensor, in automobile applications. 
         [0005]    Existing energy harvesting systems lack one or more features necessary to operate efficiently in the environment of a shock absorber. For example, some vibrational energy systems may not achieve the entire frequency range needed to efficiently harvest energy from an automobile. Another problem that exists with shock absorbers is the need to lubricate sliding surfaces of shock absorber components. Still another problem with energy harvesting in shock absorbers is controlling energy harvesting with respect to damping, as optimizing energy harvesting and optimizing damping are often competing goals. 
         [0006]    Accordingly in light of these difficulties, there exists a need for an energy harvesting shock absorber and a method for controlling such a shock absorber. 
       SUMMARY 
       [0007]    An energy harvesting shock absorber includes first and second body portions, where the second body portion defines a fluid chamber. A piston located in the fluid chamber divides the fluid chamber into first and second regions. A rod mechanically couples the piston to the first body portion. A coil surrounds at least a portion of the fluid chamber. A ferromagnetic fluid is in the fluid chamber for moving to induce a change in magnetic flux in the coil, to lubricate an inner surface of the fluid chamber, and to damp relative motion between the first and second body portions. 
         [0008]    The subject matter described herein can be implemented in software in combination with hardware and/or firmware. For example, the subject matter described herein can be implemented in software executed by a processor. In one exemplary implementation, the subject matter described herein can be implemented using a non-transitory computer readable medium having stored thereon executable instructions that when executed by the processor of a computer control the processor to perform steps. Exemplary non-transitory computer readable media suitable for implementing the subject matter described herein include chip memory devices or disk memory devices accessible by a processor, programmable logic devices, and application specific integrated circuits. In addition, a computer readable medium that implements the subject matter described herein may be located on a single computing platform or may be distributed across plural computing platforms. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The subject matter described herein will now be explained with reference to the accompanying drawings of which: 
           [0010]      FIG. 1A  is a diagram of an energy harvesting shock absorber according to an embodiment of the subject matter described herein; 
           [0011]      FIG. 1B  is a top view of a piston for an energy harvesting shock absorber according to an embodiment of the subject matter described herein; 
           [0012]      FIG. 2  is schematic diagram of an energy harvesting shock absorber according to an embodiment of the subject matter described herein; 
           [0013]      FIG. 3  is a block diagram of a system for controlling an energy harvesting shock absorber according to an embodiment of the subject matter described herein; and 
           [0014]      FIG. 4  is a flow chart illustrating an exemplary system for controlling an energy harvesting shock absorber according to an embodiment of the subject matter described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    According to the subject matter described herein, an energy harvesting shock absorber and a method for controlling such a shock absorber is provided.  FIG. 1A  is a sectional view of an energy harvesting shock absorber according to an embodiment of the subject matter described herein. Referring to  FIG. 1A , a shock absorber  100  includes a first body portion  102  that is mechanically coupled to a second body portion  104 . In particular, first body portion  102  is coupled to second body portion  104  through a piston  106  and a rod  108 . Second body portion  104  forms an internal fluid chamber  109  that piston  106  divides into an upper region  110  and a lower region  112 . A coil  114  surrounds at least portion of the fluid chamber. A force sensor  116  may be located on rod  108  to sense forces exerted on to shock absorber by the system in which it is installed. Force sensor  116  may provide force feedback to a control system to allow precise control of the level of energy harvesting from shock absorber  100  and the amount of damping force applied by shock absorber  100 . In one example, shock absorber may be mounted to an automobile. At 55 mph, force is applied to shock absorber  100  at a frequency of 15 Hz, harvested power is about 120 W, and power lost due to damping is between 100 W and 150 W. 
         [0016]    According to an aspect of the subject matter described herein, fluid chamber  109  may be at least partially filled with a ferromagnetic fluid  118 . Ferromagnetic fluid  118  may be a synthetic oil with ferromagnetic nanoparticles suspended in the oil. An example of a ferromagnetic fluid suitable for use with embodiments of the subject matter described herein is the EFH series available from Ferrotech Corporation of New Castle, Pa. Ferromagnetic fluid  118  may function as a mechanism for generating a change in magnetic flux, as a lubricant, and as a kinetic energy damping agent. For example, when piston  106  moves within fluid chamber  109 , ferromagnetic fluid  118  may be forced through holes in piston  106  between regions  110  and  112  of fluid chamber  109 . The movement of ferromagnetic fluid  118  within fluid chamber  109  changes the magnetic flux in the volume surrounded by coil  114  and induces a current in coil  114 . The induced current may be harvested by an energy harvesting control system, as will be described in detail below. The friction of fluid flowing through the holes in piston  106  may damp the kinetic energy generated by shock absorber  100  when shock absorber is coupled to a mechanical system. Ferromagnetic fluid  118  may also lubricate there interior walls of fluid chamber  109  to reduce frictional wear caused by movement of piston  106  within fluid chamber  109 . 
         [0017]    Shock absorber  100  may further include permanent magnets  119  and  120  at opposing ends of fluid chamber  109 . Permanent magnets  119  and  120  may provide a bias flux that changes when fluid  118  moves within fluid chamber  109 . Fluid chamber  109  may also include a seal  121  that seals around rod  108  to prevent leakage of ferromagnetic fluid  118 . Piston  106  may also include an electromagnetic valve  122  and holes to prevent movement of ferromagnetic fluid  118  between upper and lower regions of fluid chamber  109 . 
         [0018]    Energy harvesting shock absorber  100  may also include attachment members  123  and  124  for connecting to a system whose vibration is being damped. For example, attachment members  123  and  124  may be eyelets that are configured to receive through bolts or pins connected to a mechanical system. In an automobile, eyelet  123  may connect to the frame and eyelet  124  may connect to the suspension. Other applications of energy harvesting shock absorber  100  include motorcycles, trucks, railroad coaches, engine suspensions, and stationary objects, such as buildings, bridges, or other structures. The energy harvested by shock absorber  100  may be used to power diagnostic systems or any other suitable application. 
         [0019]    As stated above, movement of ferromagnetic fluid  118  within the volume surrounded by coil  114  causes a change in magnetic flux. To allow such movement, piston  106  may include one or more holes or apertures located in its main body to allow fluid to pass through piston  106 .  FIG. 18  is a top view of piston  106  illustrating holes  125  through which ferromagnetic fluid  118  may pass. In the illustrated example, two holes  125  are illustrated. However, any number of holes  125  may be included without departing from the scope of the subject matter described herein. Electromagnetic valve  122  may also be opened or closed to increase or decrease fluid flow between upper and lower regions of fluid chamber  109 . 
         [0020]    In  FIG. 1 , the symbol U represents a damping DC voltage applied to the coil and the symbol u represents the harvested AC voltage generated by the change in magnetic flux, which induces a current and a corresponding voltage in coil  114 . 
         [0021]      FIG. 2  is a schematic diagram of an energy harvesting shock absorber according to an embodiment of the subject matter described herein. Referring to  FIG. 2 , coil  114 , permanent magnet  120 , and fluid drop  118  are shown. The remaining components of shock absorber  100  are omitted for simplicity. Drop of ferromagnetic fluid  118  travels a distance, represented by the variable d, to a new position, represented by fluid drop  118 ′. U represents the damping DC voltage applied to the coil. As ferromagnetic fluid drop  118  moves to the position of fluid drop  118 ′, the current induced in coil  114  is proportional to the change in magnetic flux caused by the motion, which is in turn proportional to the velocity of movement of ferromagnetic fluid drop  118 . Changes in direction of fluid drop  118  causes a change in direction of induced current in coil  114 . Thus, the voltage produced across terminals of coil  114  and supplied to an external system is an AC voltage. 
         [0022]      FIG. 3  is a block diagram of a control system for controlling damping and energy harvesting by shock absorber  100 . The control system may be coupled to force sensor  116  and to coil  114 . In  FIG. 3 , an input module  126  receives input from force sensor  116  and a coil input module  128  receives input from coil  114  in the form of induced current and/or voltage. A damping calculator  130  receives the input from the coil and the force sensor and determines how much damping to apply to the system. For example, damping calculator may measure the frequency, amplitude, or phase of the damping and determine how much the actual damping level differs from a desired level. Damping calculator  130  may adjust the damping by changing the DC voltage U, changing the amount of energy harvesting, opening or closing valve  122 , or any combination thereof. Harvested energy may be stored in harvested energy store  132 . The signal to change the DC voltage applied to the coil, open or close the valve, or change the energy harvesting may be provided to input module  126  via feedback mechanism  134 . Input module  126  may change the appropriate parameter based on the signal. 
         [0023]      FIG. 4  is a flow chart illustrating exemplary steps for controlling an energy harvesting and shock absorber according to an embodiment of the subject matter described herein. Referring to  FIG. 4 , the method includes receiving coil current or voltage induced by an energy harvesting shock absorber. For example, in  FIG. 1A , current or voltage induced in coil  114  may be received by the control system illustrated in  FIG. 3 . In step  202 , the damping of the shock absorber is measured, for example, by force sensor  116  illustrated in  FIG. 1A . The frequency, amplitude, phase, or any other parameter of the damping may be measured. Combinations of parameters may also be measured. In step  204 , it is determined whether the damping currently being performed is desired. For example, it may be desirable to maintain the frequency or amplitude of travel by piston  106  within a desired range. If the damping is at the desired level, control proceeds to step  206  where energy is continued to be harvested at the current level and then to step  200  where the process is repeated. If the damping is not being performed at the desired level, control proceeds to step  208  where energy harvesting, bias voltage, and/or fluid flow are adjusted to achieve the desired damping. For example, extra DC may be applied to the coil to increase the damping, DC voltage applied to the coil may be reduced to reduce the damping, valve  122  may be opened or closed to change the fluid flow between the chambers, or energy harvesting may be increased or decreased to reduce or increase the damping. 
         [0024]    Shock absorber  100  may be coupled to any suitable mechanical system where damping is desired. Examples of mechanical system to which shock absorber  100  may be coupled include automobiles, trains, motorcycles, engine suspensions—used both in engines for transport and stationary systems. Power harvested from shock absorber  100  may be used to power an external system. For example, power harvested from shock absorber  100  may be used to power one or more lights in an automobile or to power diagnostic systems on a train. 
         [0025]    It will be understood that various details of the subject matter described herein may be changed without departing from the scope of the subject matter described herein. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation, as the subject matter described herein is defined by the claims as set forth hereinafter.