Abstract:
A magnetohydraulic motor with a positive displacement pump that pumps hydraulic fluid to and from the two sides of a bi-directional piston that provides the motor&#39;s output force and motion. Motion control is provided by properly controlling valves that selectively open and close fluid passageways between the actuator member and each side of the piston.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority of Provisional application Ser. No. 60/341,059, filed on Dec. 12, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to a magnetically-actuated hydraulic motor that provides both high force and precise position control.  
         BACKGROUND OF THE INVENTION  
         [0003]    Hydraulic motor systems typically require a large motor to pump hydraulic fluid to a piston. Accordingly, when hydraulic motor systems are used to move small or remote structures, hydraulic lines must be employed to move the hydraulic fluid from the motor to the actuated-member. These lines add weight, expense, and additional potential failure points, thus increasing the complexity, cost and size of these systems.  
         SUMMARY OF THE INVENTION  
         [0004]    Magnetic shape memory materials (SMM) are metal alloys that undergo a phase transition when exposed to moderate magnetic fields. The phase change is reversible and repeatable. Strains of several percent are available.  
           [0005]    SMMs are alloys of Nickel-Manganese-Gallium. Some SMM alloys show potential for high strain at temperatures approaching room temperature. SMMs exhibit strains that exceed the capabilities of rare-earth-based magnetostrictor materials.  
           [0006]    Unlike magnetostrictive materials in which the magnetic moment is anisotropic, a shape memory material undergoes a transformation from martensitic to a body-centered cubic structure with an accompanying volume change that can be as high as 5%. This order-of-magnitude higher change translates into more compact actuators that have wide applications for vibration control, electromechanical devices, robotics, etc.  
           [0007]    Bulk samples of this alloy have been fabricated by weighing out the appropriate combination of the nickel, manganese and gallium and arc melting under an argon atmosphere. The alloy was re-melted several times to ensure a good alloy blend and then chill cast into a copper mold.  
           [0008]    The magnetostriction of this material composition was measured under an applied magnetic field of 3 kOe and an elongation of 0.7% was observed. By changing the relative amount of manganese, nickel and gallium, the phase transition can be shifted in temperature and broadened to fit the needs of various applications.  
           [0009]    This invention features a magnetohydraulic motor that provides high force actuation. The motor can be used in any relevant application, one of which is for aircraft flight control surfaces. The basic concept of the inventive motor is as follows. The motor consists of a pump operated by a shape-changing material, a pair of flow control valves and a piston that amplifies the force and displacement. Magnetic shape memory materials are preferably used to pressurize and move the hydraulic fluid into and out of the piston.  
           [0010]    The positive displacement SMM pump is the heart of the inventive motor. It consists of a rod of shape memory material enclosed in a sealed shell, with two valves at one end. The SMM is not constrained, except at one end where it is bonded to the shell. An external coil is used to impose a magnetic field on the SMM. Activation of the SMM pump via an electrical current induces the SMM to extend or contract. The pump can provide pressure and flow on demand.  
           [0011]    In operation, the pump would be excited by an oscillating current, which in turn causes the pump to push the hydraulic fluid in an oscillating manner at twice the frequency of the AC current. This occurs because the SMM changes its length in proportion to the amplitude of the magnetic field.  
           [0012]    There are two flow control valves. These valves are driven open and closed at a frequency equal to the pumping frequency. The timing of the valves corresponds to the pressure cycle in the pump so that the maximum flow and pressure can be delivered to the piston.  
           [0013]    The piston serves to amplify the stroke and force capability of the SMM pump. By continuously pumping in one direction, the piston can be moved a relatively great distance depending on the motor design, and the pump flow rate and frequency.  
           [0014]    One of the advantages of this valving scheme is that to reverse direction of actuation, only the timing of the valves needs to be changed. Thus, the response time to any change can be very rapid. This timing sequence can be controlled by a standard digital controller.  
           [0015]    In an alternate embodiment, the shape memory material of the pump is used to move a bellows back and forth rather than to directly pump the hydraulic fluid. This configuration magnifies the SMM movement, and thus is desirable when the volume change of the shape memory material is negligible, or insufficient for the desired pumping flow rate.  
           [0016]    Another alternative embodiment can be accomplished by replacing the magnetic shape memory material with a magnetostrictive material. Although the dimensional change of the magnetostrictor is less than the shape memory material, the pump will still function in the same manner, but with reduced motion capability.  
           [0017]    Other embodiments can be accomplished by replacing the magnetic shape memory material and its coil with a piezoelectric or electrostrictive actuator. These materials change shape upon application of an electric field as opposed to a magnetic field. Because the strains are extremely small, significant elongation requires that the actuator member comprise a number of piezoelectric or electrostrictive portions arranged in series, and each connected across a voltage source.  
           [0018]    The advantages of the invention are:  
           [0019]    high strain material is used to provide high pumping capacity;  
           [0020]    compact motor size;  
           [0021]    high speed response to changes in direction;  
           [0022]    by operating the SMM pump at a constant frequency equal to its mechanical resonance, the efficiency can be maximized;  
           [0023]    a small digital controller and electrical controls eliminate hydraulic lines and their associated weight and inefficiency. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    Other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiments and the accompanying drawings in which:  
         [0025]    [0025]FIG. 1 is a schematic, cross-sectional view of the preferred embodiment of the magnetohydraulic motor of this invention;  
         [0026]    [0026]FIG. 2 is a similar view of an alternative embodiment that employs a bellows to magnify the actuator motion;  
         [0027]    [0027]FIG. 3 is a series of graphs showing one embodiment of the pump motion and valve control for the magnetohydraulic motors of FIGS. 1 and 2; and  
         [0028]    [0028]FIG. 4 is an enlarged, schematic, cross-sectional view of a piezoelectric or electrostrictive-based shape-changing actuator member for the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    This invention may be accomplished in a magnetohydraulic motor that can be an extremely small size yet accomplish high force, rapid response time, and minutely-controllable position. These aims are accomplished by using a shape-changing material in the pump actuator member. These materials include shape memory materials (SMM), magnetostrictive materials, piezoelectric materials, and electrostrictive materials. Each of these materials changes shape upon the application of an electrically-derived magnetic or electrical field, as appropriate for the material. These materials have high force output and small but controllable and repeatable motions that can translate into pumps with an output that accomplishes these advantages.  
         [0030]    There is shown in FIG. 1 magnetohydraulic motor  10  according to this invention. Motor  10  comprises positive displacement pump  11  and hydraulic piston portion  13 . Pump  11  comprises actuator-housing  12  that holds shape-changing actuator member  16  surrounded by coil  24  that selectively applies a magnetic field to actuator member  16 . Member  16  is anchored at end  20  to housing  12  with the other end  22  free to move upon the application of the magnetic field. Hydraulic fluid chamber  18  is in fluid communication with actuator member  16  so that motion of member  16  causes pumping of fluid in chamber  18  through one or both of fluid communication channels  30  and  32 . Channels  30  and  32  lead to fluid chambers  34  and  36 , respectively, that are on either side of piston  40  having fluid-actuatable surfaces  41  and  43  and piston output numbers  42  and  44 . Passageways  30  and  32  can be selectively opened and closed with electrically-operable valves  31  and  33 , respectively.  
         [0031]    Valves  31  and  33  may each comprise a shape-changing valve actuator member fixed at one end, with the other end coupled to a movable closure member that is adapted to close and open the fluid communication passageway. The valves could be accomplished in other manners such as with more traditional solenoid-actuated closure members that can also be more traditional valve-member constructions. Non-limiting examples include ball valves, gate valves, and butterfly valves.  
         [0032]    An alternative preferred embodiment is shown in FIG. 2. The difference is that in this case actuator-member  16  is coupled at its free end  22  to bellows members  50  that moves fluid in chamber  18   a . The bellows can magnify the relatively small displacement of the actuator member to accomplish greater fluid displacement for a desired purpose.  
         [0033]    [0033]FIG. 3 shows one pump actuation and valve control scheme useful for any embodiment of the invention. In this case, the pump actuator member is excited by an oscillating current. The valves are opened and closed at a frequency equal to the pumping frequency. The timing of the valves corresponds to the pressure cycle in the pump. This achieves maximum hydraulic fluid flow and pressure, which translates to maximum force and speed of the piston. Other control schemes are possible depending on the desired use of the motor. For example, in instances in which force needs to be applied in only one direction, the piston can have only one force-actuating surface. There could be a single fluid communication channel and a single valve that was opened only during the pressure cycle of the pump. This can cause small or large motions of the piston. The pressure could be relieved by opening the valve when the actuator member is relaxed.  
         [0034]    [0034]FIG. 4 schematically depicts a piezoelectric or electrostrictive shape-changing actuator member  80  that comprises a large number of sections of piezoelectric or electrostrictive material arranged so that their motions are additive. These sections are placed across positive and negative electrodes  82  and  84  so that the proper voltage differential can be placed across the elements as necessary to accomplish a shape change, as would be known by those skilled in the art.  
         [0035]    Although specific features of the invention are shown in some drawings and not others, this is for convenience only as some feature may be combined with any or all of the other features in accordance with the invention.  
         [0036]    Other embodiments will occur to those skilled in the art and are within the following claims: