Abstract:
A hydraulic actuator has an armored section having concentric cylinders and an unarmored section having a cylinder with a frangible piston and a frangible upper gland nut. The hydraulic actuator may have leakage vents adapted to prevent leakage between hydraulic systems used to power the cylinders. The hydraulic actuator also may have a gland seal for sealing an end of the cylinder of the unarmored section and a sensing port adapted for allowing detection of fluid leaking due to damage of the gland seal.

Description:
TECHNICAL FIELD 
     The technical field is ballistically tolerant linear hydraulic actuators. 
     DESCRIPTION OF THE PRIOR ART 
     Many types of linear hydraulic actuators are used in aircraft for positioning aircraft components. These may include components such as flight control surfaces, speedbrakes, and landing gear. In order to provide for redundancy in the systems, dual or triple actuators will often be used, and these may be used with two or more hydraulic systems for powering the actuators. 
     One example of a dual concentric actuator, which is shown in  FIG. 1 , has been used for speedbrakes on the Boeing F/A-18 aircraft. Actuator  11  comprises a central hydraulic retract chamber  13  having a piston  15  fixed to the stationary end and a concentric outer hydraulic actuator retract chamber  17  having a piston  19  attached to the moving end. For actuator extension there is a single extend chamber  20 . 
     Currently there are two technologies utilized to provide triplex redundancy for critical flight control actuators used on helicopters and tiltrotors.  FIG. 2  shows a prior-art configuration of a hydraulic actuator system  21  for flight control actuators  23 ,  25  as used on the Bell/Boeing V-22 tiltrotor aircraft. System  21  is used, for example, to position a flight control device  27 . Because configuring three actuator cylinders end-to-end in tandem results in an excessively large actuator envelope, system  21  uses a dual tandem actuator  23  and uses a switching valve  29  to allow one of two different hydraulic systems  31 ,  33  to power one of the two cylinders within actuator  23 . The configuration of system  21  does not provide full-triplex redundancy and is therefore not as reliable as a true triplex actuator system. 
       FIG. 3  shows a prior-art configuration of a hydraulic actuator system  35  for flight control actuators  37 ,  39 ,  41  as used on the Bell/Agusta BA609 tiltrotor aircraft. System  35  is used, for example, to position a flight control device  43 . System  35  provides a compact fully-triplex actuator system by positioning the three cylinders  45 ,  47 ,  49  side by side in a triangular configuration, and this configuration provides higher reliability than the dual tandem with switching valve configuration of system  21  of  FIG. 2 . However, because all three exposed rams  51 ,  53 ,  55  and cylinders  45 ,  47 ,  49  must be armored or otherwise designed to provide ballistic protection, this configuration does not lend itself to military applications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of a prior-art dual concentric hydraulic actuator. 
         FIG. 2  is a schematic view of a prior-art configuration of a hydraulic actuator system. 
         FIG. 3  is a schematic view of a prior-art configuration of a hydraulic actuator system. 
         FIG. 4  is a schematic cross-sectional view of an embodiment of a ballistically tolerant hydraulic actuator. 
         FIG. 5  is a detailed cross-sectional view of an embodiment of a ballistically tolerant hydraulic actuator. 
         FIG. 6A  is an enlarged schematic cross-sectional view of a portion of the ballistically tolerant hydraulic actuator of  FIG. 5 . 
         FIG. 6B  is an enlarged schematic cross-sectional view of a portion of the ballistically tolerant hydraulic actuator of  FIG. 5 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     To overcome the ballistic issues with side-by-side, parallel-configuration actuators, an embodiment of an actuator provides a triplex tandem actuator that fits in an actuator envelope only slightly larger than a V-22 dual tandem actuator having the same stroke length. The triplex tandem actuator configuration with concentric lower cylinders provides improved ballistic tolerance by providing two armored cylinders plus one unarmored cylinder, as compared to the current V-22 configuration, in which one armored cylinder and one unarmored cylinder are used. Additionally, the actuator has through-the-ram leakage vent holes to prevent intersystem leakage and a sensing port for sensing when there is a damaged upper gland seal. Reliability is also improved by the elimination of switching valves and by providing full triplex redundancy. 
       FIG. 4  is a schematic cross-sectional view of an embodiment of a triplex tandem actuator  57 . Actuator  57  comprises a dual concentric cylinder configuration in an armored section  59  and a single cylinder configuration in an unarmored section  61 . Armored section  59  comprises an armored outer wall  63  that minimizes the damage caused by ballistic impacts to section  59 . Armored wall  63  may be formed of any appropriate material, such as armor plating, and encloses a volume divided into two concentric actuator cylinders, whereas unarmored section  61  comprises an outer wall  65  that encloses a volume configured to act as one actuator cylinder. Sections  59 ,  61  are joined to each other in a coaxial arrangement. 
     A ram  67  extends through section  61  and into section  59 . Ram  67  has a cylindrical portion  69  located within section  61 , and a circumferential, frangible piston  71  is formed on an outer surface of cylindrical portion  69 . Piston  71  has opposing surfaces  73 ,  75 , and piston  71  is sealed to an inner surface of outer wall  65  with seal  77 , defining annular fluid volumes  79 ,  81  within section  61 . An extend port  83  extends through outer wall  65  and communicates with fluid volume  79 , and a retract port  85  extends through outer wall  65  and communicates with fluid volume  81 . A seal  87  sealingly engages ram  67  and outer wall  65 , and this seals the end of fluid volume  79  opposite piston  71 . A frangible nut and gland seal assembly  89  also sealingly engages ram  67  and outer wall  65  for sealing the end of fluid volume  81  opposite piston  71 . 
     Ram  67  has a skirt portion  91  that extends into section  59  and terminates in a piston  93 . An outer surface of piston  93  is sealed to outer wall  63  with seal  95 , and skirt  91  is sealed to outer wall  63  with seal  97 . Skirt  91  encloses an inner valve member  99  that is connected to outer wall  63  and terminates in a piston  101 . A seal  103  sealingly engages piston  101  to an inner surface  105  of skirt  91 , defining a fluid volume  109 . A seal  111  seals an inner surface of piston  93  of ram  67  to valve member  99 , and seals  103 ,  111  cooperate to define annular fluid volume  113 . Seals  95 ,  97  cooperate to define annular fluid volume  115 , and seals  95 ,  111  cooperate to define annular fluid volume  117 . 
     An extend port  119  extends through outer wall  63  and communicates with fluid volume  117 , and a retract port  121  extends through outer wall  63  and communicates with fluid volume  115 . Pressure in fluid volume  117  acts on surface  123  of piston  93 , and pressure in fluid volume  115  acts on surface  125  of piston  93 . 
     An extend port  127  extends through valve member  99  and communicates with fluid volume  109 , and a retract port  129  extends through valve member  99  and communicates with fluid volume  113 . Pressure in fluid volume  109  acts on piston surface  131  of ram  67 , and pressure in fluid volume  113  acts on surface  133  of piston  93 . 
     In operation, ram  67  may be extended by applying fluid pressure through any one of extend ports  83 ,  119 , and  127  and into the corresponding fluid volumes  79 ,  109 ,  117 . The fluid pressure acts on the associated piston surface  73 ,  123 ,  131  to cause ram to extend out of actuator  57 . Likewise, ram  67  may be retracted by applying fluid pressure through any one of retract ports  85 ,  121 , and  129  and into the corresponding fluid volumes  81 ,  113 ,  115 . The fluid pressure acts on the associated piston surface  75 ,  125 ,  133  to cause ram to retract into actuator  57 . In the event of ballistic damage to unarmored section  61 , ram  67  may still be extended and retracted using the cylinders within armored section  59 . If one of the concentric cylinders within armored section  59  is damaged, the other of the cylinders may still be used to position ram  67 . 
       FIG. 5  is a detailed cross-sectional view of another embodiment of a triplex tandem actuator, and  FIGS. 6A and 6B  are enlarged, detailed, cross-sectional views of the actuator of  FIG. 5 . 
       FIG. 5  shows a triplex tandem actuator  135  that has a similar configuration to actuator  57 , which is described above. Actuator  135  comprises a dual concentric cylinder configuration in an armored section  137  and a single cylinder configuration in an unarmored section  139 .  FIG. 6A  is an enlarged view of unarmored section  139 , and  FIG. 6B  is an enlarged view of unarmored section  137 . 
     Unarmored section  139  has an unarmored outer wall  141  that forms a single cylinder actuator for moving ram  143 . An extend port  145  extends through outer wall  141  and communicates with annular fluid volume  147 , and a retract port  149  extends through outer wall  141  and communicates with annular fluid volume  151 . In a similar manner to that described above for actuator  57 , pressure in fluid volume  147  acts on the corresponding surface of a frangible piston  153  to extend ram  143 , and pressure in fluid volume  151  acts on the opposite surface of piston  153  to retract ram  143 . A frangible nut and gland seal assembly  155  is used to seal the end of fluid volume  151  opposite piston  153 . A leakage vent  157  is provided in ram  143  to allow for venting of fluid that has leaked from the hydraulic system in section  139 . Also, a sensing port  159  is provided in outer wall  141  for allowing sensing of fluid leakage indicative of a damaged gland seal in assembly  155 . A triplex linear variable differential transformer  161  is provided for measuring the amount of displacement of ram  143  during operation of actuator  135 . 
     Use of sensing port  159  allows for protection of the hydraulic system powering section  139 . If flow to port  159  (indicating a damaged gland seal assembly  155 ) is detected, a flight control computer can configure a manifold (not shown) feeding section  139  into a bypass/shutoff configuration to isolate the leak. This keeps section  139  from depleting the fluid in the system following damage to gland seal assembly  155  and isolates the leak at its source. 
     Armored section  137  has an armored outer wall  163  that forms a dual concentric cylinder actuator for moving ram  143 . An extend port  165  extends through outer wall  163  and communicates with annular fluid volume  167 , and a retract port  169  extends through outer wall  163  and communicates with annular fluid volume  171 . A valve member  173  is located within a skirt portion  175  of ram  143 , and an extend port  177  and a retract port  179  extend through valve member  173 . Valve member  173  is attached to outer wall  163  and does not move with ram  143 . Extend port  177  communicates with fluid volume  181 , and retract port  179  communicates with annular fluid volume  183 . In a similar manner to that described above for actuator  57 , pressure in fluid volume  167  acts on the corresponding surface of a piston  185  to extend ram  143 , and pressure in fluid volume  171  acts on an opposite surface of piston  185  to retract ram  143 . Likewise, pressure in fluid volume  181  acts on inner surface  187  of ram  143  to extend ram  143 , and pressure in fluid volume  183  acts on a corresponding surface of piston  185  to retract ram  143 . A leakage vent  189  is provided near the interface of section  137 ,  139  to allow for venting of fluid that has leaked from either or both hydraulic systems in section  137 . 
     In the preferred embodiment, the size and weight of the triplex tandem actuator cylinder assembly is only slightly more that a similar dual tandem actuator. The required large ram diameter creates the space required for the third cylinder within the ram. Because the V-22 and many new aircraft will be using hydraulic systems operating in the range of 5,000 psi, very little effective piston area is required to produce desired cylinder operation. The only significant weight difference between a dual tandem actuator and the triplex tandem actuator is the addition of a third control manifold to operate the third cylinder, though this weight gain is balanced by the elimination of switching and isolation valves. 
     Whether dual or triplex in configuration, each actuator cylinder is to be sized by the load required for safe operation on one operating cylinder. Because the armor of the armored section protects two systems, damage to the unarmored section does not significantly degrade the flight envelope. 
     The triplex tandem actuator provides for several advantages, including: 1) providing critical flight control actuation for military aircraft requiring ballistic protection; 2) providing increased reliability with no significant envelope or weight impact; and 3) providing ballistic protection with no significant envelope or weight impact. 
     This description includes reference to illustrative embodiments, but it is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments, will be apparent to persons skilled in the art upon reference to the description.