Abstract:
A rotary hydraulic actuator includes a housing defining a chamber, a first boss, and a port block with a bore communicating with the chamber. The port block includes rotor supply and drain ports communicating with the bore, and a stator port communicating with the chamber through a stator hole in the boss. A rotor mounted in the internal chamber includes: a body with a laterally-extending arm; a first stub shaft received in the bore, the first stub shaft including base slots passing laterally therethrough; a first rotor port disposed in the arm in communication with the internal chamber, and oriented in a tangential direction relative to an axis of rotation; and internal passages which interconnect the rotor base slots and the first rotor port. Passages in the port block communicate with the bore and interconnect the rotor supply and drain ports at a first angular position of the rotor.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to hydraulic actuators and more particularly to motion control for such actuators. 
         [0002]    Aircraft powerplants are typically used to drive thrust-generating airfoil elements such as propellers or fan blades. It is known to vary the angle of incidence (i.e. “pitch angle”) of the airfoil elements relative to the rotating hub carrying them, in order to provide the maximum possible propulsive efficiency at various flight conditions. 
         [0003]    A common method of pitch control employs a hydraulic actuator which changes the blade pitch angle in response to pressurized fluid flow. The actuator may move the blade through pitch angles from “coarse” to “fine” and may also provide pitch angles suitable for ground operation. For safety reasons, it is important to limit the blade pitch angle during flight. This avoids overspeeding the powerplant, or imposing excessive structural loads or unexpected yawing moments to the aircraft. A typical prior art variable-pitch propeller includes a mechanical pitch stop or lock which limits the blade pitch angle and must be manually retracted in order to move the blades towards positions in the ground operating range. 
         [0004]    While mechanical pitch stops are effective, they add complexity, weight, and cost to the basic actuator device. Accordingly, there is a need for an actuator which provides two ranges of rotary movement without a mechanical lock or stop to define the limit between ranges. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    This need is addressed by the present invention, which provides a rotary actuator having two ranges of operation, where the limit between the ranges is controlled hydraulically. 
         [0006]    According to one aspect of the invention, a rotary hydraulic actuator apparatus includes: a housing including: a peripheral wall and an end wall which cooperatively define a generally cylindrical internal chamber, where a first boss extends radially inward from the peripheral wall; and a port block defining a cylindrical bore communicating with the end wall, the port block further including a rotor supply port and a rotor drain port communicating with the bore, and a stator port communicating with the internal chamber through a stator hole in the boss. A rotor is mounted for rotation in the internal chamber about an axis of rotation, the rotor including: a body with an arm extending laterally-outward therefrom; a first stub shaft which is received in the bore of the housing, the first stub shaft including base slots passing laterally therethrough; a first rotor port which is disposed in the arm in communication with the internal chamber, and oriented in a tangential direction relative to the axis of rotation; and internal passages which interconnect the rotor base slots and the first rotor port. Passages in the port block communicating with the bore are configured to interconnect the rotor supply port and the rotor drain port through the rotor base slots, at a preselected first angular position of the rotor relative to the housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
           [0008]      FIG. 1  is perspective exterior view of a rotary hydraulic actuator constructed according to an aspect of the present invention; 
           [0009]      FIG. 2  is a perspective view of the actuator of  FIG. 1 , with a cover thereof removed; 
           [0010]      FIG. 3  is a perspective view of a rotor of the actuator of  FIG. 1 ; 
           [0011]      FIG. 4  is a schematic cross-sectional view of the actuator taken through a middle portion thereof, with the rotor in a first position; 
           [0012]      FIG. 5  is a schematic cross-sectional view of the actuator of  FIG. 1 , taken through an end portion thereof, with the rotor in a first position; 
           [0013]      FIG. 6  is a schematic cross-sectional view of the actuator taken through a middle portion thereof, with the rotor in a second position; 
           [0014]      FIG. 7  is a schematic cross-sectional view of the actuator of  FIG. 1 , taken through an end portion thereof, with the rotor in a second position; 
           [0015]      FIG. 8  is a schematic cross-sectional view of the actuator taken through a middle portion thereof, with the rotor in a third position; 
           [0016]      FIG. 9  is a schematic cross-sectional view of the actuator of  FIG. 1 , taken through an end portion thereof, with the rotor in a third position; 
           [0017]      FIG. 10  is a schematic cross-sectional view of the actuator taken through a middle portion thereof, with the rotor in a fourth position; 
           [0018]      FIG. 11  is a schematic cross-sectional view of the actuator of  FIG. 1 , taken through an end portion thereof, with the rotor in a fourth position; and 
           [0019]      FIG. 12  is a schematic view of a rotary hydraulic actuator coupled to a pump and valve system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIGS. 1 and 2  depict a rotary hydraulic actuator  10  constructed according to the invention. The major components of the actuator  10  are a housing  12  and a rotor  14 . As described in more detail below, the actuator  10  is operable to produce controlled rotary motion of the rotor  14  when the actuator  10  is provided with a flow of pressurized hydraulic fluid to its various ports. While it may be used for any mechanical load that requires rotary motion, the actuator  10  is particularly useful for controlling the pitch angle of an airfoil, such as gas turbine engine fan blade or a propeller blade (not shown). 
         [0021]    The housing  12  has an inboard end  18  and an outboard end  20 , and is assembled from a base  22  and a cover  24  which are assembled to each other by bolts or other suitable fasteners. The housing  12  has a peripheral wall  26  and an end wall  28  which cooperatively define a generally cylindrical internal chamber  30 . Two opposed bosses  32  and  34  protrude towards the center of the otherwise cylindrical internal chamber  30 . Each boss  32 ,  34  is wedge-shaped with two spaced-apart planar side walls  36  and a concave-curved end wall  38 . One of the bosses  32  has a stator supply hole  40  formed therein (best seen in  FIG. 4 ). The stator supply hole  40  is open to the interior of the internal chamber  30  and also communicates, through internal passages which are not shown, with a stator port  42  (seen in  FIG. 1 ). It should be noted that terms such as “supply” and “drain”, as used herein, serve merely as a convenient reference and do not necessarily describe the sole function of a particular port or structure. 
         [0022]    A port block  44  protrudes from the end wall  28  of the base  22 . As best seen in  FIG. 5 , the port block  44  includes a closed-ended cylindrical bore  46 . A rotor supply groove  48  extends around a portion of the bore  46 , and communicates with both the bore  46  and a rotor supply port  50 . A rotor drain groove  52  extends around a portion of the bore  46 , and communicates with both the bore  46  and a rotor drain port  54 . 
         [0023]    The rotor  14  is shown in  FIG. 3 . It has a generally cylindrical body  56  with inboard and outboard stub shafts  58  and  60  extending from opposite ends thereof The body  56  is sized to be received between the bosses  32 ,  34 , and two generally rectangular arms  62  extend laterally from the body  56  in opposite directions. The outboard stub shaft  60  is adapted to be coupled to a mechanical load to be rotated, such as a fan or propeller blade. The inboard stub shaft  58  is sized to be received in the bore  46  of the port block  44 . The rotor  14  may include different numbers of arms to suit a particular application; for example only one arm, or more than two arms may be provided. In general the housing  12  would include one boss for each arm of the rotor  14 . 
         [0024]    The rotor  14  includes several internal passages. A central gallery  64  extends upward through the inboard stub shaft  58  and partway into the body  56 . Diametrically-opposed base slots  66  extend between the central gallery  64  and the outer peripheral surface of the inboard stub shaft  58 . An inboard lateral gallery  68  extends from one arm  62  through the body  56  and the central gallery  64  into the opposite arm  62 . An inboard rotor port  70  extends from each end of the inboard lateral gallery  68 , in a direction perpendicular to the inboard lateral gallery  68  (i.e. tangential to an axis of rotation of the rotor  14 ), and is open to the exterior of the associated arm  62 . An outboard lateral gallery  72  extends from one arm  62  through the body  56  into the opposite arm  62 . An outboard rotor port  74  extends from each end of the outboard lateral gallery  72 , in a direction perpendicular to the outboard lateral gallery  72  (i.e. tangential to an axis of rotation of the rotor  14 ) and is open to the exterior of the associated arm  62 . The ends of the lateral galleries  68  and  72  may be open or may be closed off with plugs. 
         [0025]    When assembled into the housing  12  the rotor  14  is free to rotate about its axis of rotation, which is parallel to the stub shafts  58  and  60 , between two limiting positions at which the arms  62  contact the bosses  32  and  34 . The arms  62  effectively divide the internal chamber  30  into four separate cavities. The size of these cavities will change as the rotor  14  moves. Solely for the sake of reference, the cavities are labeled in  FIG. 2  as “A”, “B”, “C”, and “D”. 
         [0026]    Means are provided for selectively porting pressurized hydraulic fluid to the actuator  10 .  FIG. 12  shows schematically a system which includes a pump  76 , three three-position valves  78 ,  80 , and  82  which are coupled to the rotor supply port  50 , rotor drain port  54 , and stator port  42 , respectively, and a reservoir  84 . Each valve  78 ,  80 , and  82  is operable to connect the associated port to the pump outlet pressure or the reservoir  84 . The valves  78 ,  80 , and  82  may be operated by any convenient means, such as manual, hydraulic, or electric control. While this simple schematic system is used to explain the basic hydraulic operation of the actuator  10 , it will be understood that other control systems may be provided in order to incorporate the actuator  10  within a practical aircraft system. In particular, a propeller governing or constant-speed mechanism of a known type may be provided. 
         [0027]    The general operation of the actuator  10  will now be described with reference to  FIGS. 2-11  and in the context of using the actuator  10  to control the position of a propeller blade (not shown). As shown in  FIGS. 4-11 , the direction of aircraft flight would be towards the left of the page, and the direction of propeller rotation would be towards the top of the page. Within  FIGS. 4-11 , the upper figure in each pair figures depicts the actuator  10  at one cross-section through the arms  62 , and the lower figure of the pair depicts the actuator  10  at a cross-section through the inboard stub shaft  58 . Rotating the rotor  14  counter-clockwise would be considered increasing the pitch angle (e.g. “coarse pitch”) and rotating the rotor  14  clockwise would be considered decreasing the pitch angle (e.g. “fine pitch”). 
         [0028]    To move the rotor  14  clockwise, the rotor supply port  50  is pressurized by coupling it to the pump output pressure, the rotor drain port  54  is coupled to the reservoir  84 , and the stator port  42  is coupled to the reservoir  84 . This causes pressurized fluid to flow through the rotor base slots  66 , and into the inboard lateral galleries  68 , and then finally out the inboard rotor ports  70 . The fluid exiting the inboard rotor ports  70  fills cavities B and D (see  FIG. 2 ). The resulting fluid pressure on the arms  62  drives the rotor  14  clockwise. As this is happening, the arms  62  displace fluid from the opposed cavities A and C. The fluid displaced from cavity A flows out through the stator supply hole  40  and thence to the stator port  42 . The fluid displaced from cavity C flows into an outboard rotor port  74 , across the outboard lateral gallery  72 , out the opposed outboard rotor port  74 , and then out through the stator supply hole  40  and thence to the reservoir  84 . 
         [0029]    To move the rotor  14  counter-clockwise the following events happen: The rotor supply port  50  is coupled to the reservoir  84  the rotor drain port  54  is also open to the reservoir  84 , and the stator port  42  is pressurized by coupling it to the pump output pressure. This causes pressurized fluid to flow out of the stator supply hole  40  and fill cavity A. Some of the fluid flows into an outboard rotor port  74 , across the outboard lateral gallery  72 , and out the opposed outboard rotor port  74  into cavity C. The resulting fluid pressure on the arms  62  drives the rotor  14  counter-clockwise. As this is happening, the arms  62  displace fluid from the opposed cavities B and D. Fluid displaced from cavities B and D flows into the inboard rotor ports  70 , into the inboard lateral galleries  68 , then the central gallery  64 , to the rotor base slots  66 , and then out either the rotor supply port  50 , the rotor drain port  54 , or both (depending on the position of the rotor  14 ). 
         [0030]    Referring to  FIGS. 4 and 5 , the rotor  14  is depicted in a fully counter-clockwise position corresponding to a propeller “high pitch” or “full coarse” position. In this position, further counter-clockwise movement is prevented by interference of the rotor  14  and the bosses  32  and  34 . This is considered a “hard stop”. 
         [0031]      FIGS. 6 and 7  depict the rotor  14  at a “full fine” or minimum flight pitch position. In this position, the base slots  66  connect the rotor supply groove  48  and the rotor drain groove  52 , and thus interconnect the rotor supply port  50  and the rotor drain port  54 . If the fluid supply is configured for clockwise motion as described above, any pressurized fluid from the rotor supply port  50  will bypass the rotor  14  and drain directly back to the reservoir  84 . As a result, no further clockwise rotation occurs. Conversely, if the fluid supply is configured for counter-clockwise motion as described above, operation will be normal. In effect there is a “hydraulic” or “soft stop” limit to clockwise rotation. The range of motion between the counter-clockwise limit shown in  FIGS. 4 and 5 , and the clockwise limit shown in  FIGS. 6 and 7  can be conceptualized as a first range of motion, which would correspond to an in-flight pitch angle range. 
         [0032]      FIGS. 8 and 9  show how a transition can be made from the “soft stop” described above to permit further clockwise motion. In practice, positions further clockwise would be needed to provide low blade pitch angles (e.g. for “ground fine” or “beta” operation), or to provide reverse thrust. In this position, the rotor supply port  50  and the rotor drain port  54  are both pressurized and the stator port  42  is coupled to the reservoir  84 . The rotor drain port pressure balances the rotor supply port pressure, which allows pressurized fluid to flow into the central gallery  64  and effectuate further clockwise movement of the rotor  14 , as described above. 
         [0033]      FIGS. 10 and 11  depict the rotor in the maximum clockwise or “max reverse” position. In this position, further clockwise movement is prevented by interference of the rotor  14  and the bosses  32  and  34 . This is considered a “hard stop”. The range of motion between the counter-clockwise limit shown in  FIGS. 4 and 5 , and the clockwise limit shown in  FIGS. 10 and 11  can be conceptualized as a second range of motion, greater than the first range described above. 
         [0034]    The actuator  10  described above provides two different available ranges of motion. When in the limited mode, the actuation angle is less than when it is not limited. This limit is imposed using entirely hydraulic control, avoiding the weight, complexity, and complication associated with a prior art mechanical stop. This actuator will be especially useful to provide compact, simple pitch control of aircraft propellers and fan blades. 
         [0035]    The foregoing has described a rotary hydraulic actuator. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation.