Abstract:
A vane type hydraulic rotary actuator incorporates a fail-safe brake for preventing movement of the device&#39;s rotor relative to a housing in which the rotor is journaled. The brake has a spring-biased piston that is forced to a locked condition whenever applied hydraulic operating pressure acting on the vane falls below a predefined limit. The rotary actuator also incorporates an improved sealing arrangement that prevents egress of hydraulic fluid from a high pressure chamber on one side of the vane to a low pressure chamber on the opposite side of the vane.

Description:
BACKGROUND OF THE INVENTION  
       [0001]    I. Field of the Invention 
         [0002]    The present invention relates generally to a hydraulic rotary actuator of the vane type, and more particularly to such a rotary actuator having improved seal structures and a fail-safe brake mechanism. 
         [0003]    II. Discussion of the Prior Art 
         [0004]    Hydraulic rotary actuators find application in a number of fields where it is desired to rotate a load through a predetermined angle relative to a stationary frame member. For example, a few applications use rotary actuators for controlling the positioning of a bucket on the end of a boom on a power company&#39;s utility truck, the rotation of the bucket on a backhoe and tipping refuse containers on refuse collection vehicles. 
         [0005]    A typical vane-type hydraulic rotary actuator comprises a stator housing with a rotor journaled for rotation within the housing that defines an annular chamber between the rotor surface and the stator. Affixed to the rotor and cooperating with a cylindrical wall of the stator is a vane that divides the chamber into a pair of hydraulic fluid receiving chambers. Also disposed in the chamber and fixedly attached to the stator is a stop having opposed ends separated by a predetermined arc. Injection of high pressure hydraulic fluid into one of the pair of chambers forces the vane and, therefore, the rotor to shift through a predetermined angle until the vane strikes a first end of the stop. The movement of the vane also forces hydraulic fluid, now at a low pressure, out from the other of the two chambers. By reversing the chamber to which the high pressure hydraulic fluid is applied, the vane will now move in the opposite direction until reaching the other end of the stop. A typical prior art example of a vane type rotary actuator is disclosed in the French U.S. Pat. No. 3,198,090. 
         [0006]    Also known in the art is the need for effective seals for preventing leakage of the high pressure hydraulic fluid past the vane which seriously detracts the efficiency of the hydraulic actuator and results in rotor drift. The sealing arrangements to date have an inherent leak path near the base of the vane where the shaft protrudes from the actuator. It is very difficult to prevent leakage across the vane and along the shaft (out of the actuator unit). 
         [0007]    Furthermore, a need exists for an effective brake arrangement that will lock the rotor relative to the stator in the event of a loss of pressure, such as may result from a leak in a hydraulic line or the intended stoppage of the rotor with the vane part way between the opposed ends of the stop. Because seal leakage can result in unwarranted drifting of the load, it is known in the art to provide a brake arrangement or the incorporation of counterbalance valves. U.S. Pat. No. 3,179,018 to Rumsey describes a hydraulic rotary actuator that incorporates a hydraulic braking system for locking the rotor in any position throughout the operating range of the rotary actuator. By applying hydraulic fluid under pressure to a piston secured to the rotor, it is brought into contact with a brake shoe forming a part of the stator housing. The implementation disclosed in the &#39;018 patent requires the application of hydraulic pressure to the brake assembly at all times, except when it is desired to reposition a load using the hydraulic actuator. Should the hydraulic brake line fail, the load would be free to swing which, of course, is highly undesirable and unsafe. 
         [0008]    A need, therefore, exists for a vane-type hydraulic actuator having an internal brake that is fail safe, i.e., the brake force is applied to lock the rotor in the event that hydraulic pressure releasing the brake falls. 
       SUMMARY OF THE INVENTION  
       [0009]    In accordance with the present invention, there is provided a rotary actuator comprising a housing defining a cylindrical bore in which a spool member is rotatably mounted. A vane is attached to the spool member and projects radially outward therefrom. Also mounted within the cylindrical bore and attached to the housing so as to project radially inward toward the spool member is a stop that has first and second end surfaces circumferentially spaced from one another and defining a gap through which the vane is free to move. The stop member includes first and second passageways for hydraulic fluid, each leading from an inlet port to an outlet port where the outlet ports are on respective ones of the first and second end surfaces. 
         [0010]    The present invention utilizes continuous seals around the ends of the vane to prevent leakage across the vane and around the pool (shaft) to prevent external leakage. The slow rotational movement of this type of actuator allows for the vane seal to seal against the spool seal. Any inherent leak is thereby minimized. 
         [0011]    The rotary actuator of the present invention further includes a hydraulically-actuated, spring-biased, friction brake mechanism that is operatively deployed between the housing and the spool member for preventing rotation of the spool member relative to the housing whenever hydraulic fluid pressure is being applied to an inlet port below a predetermined pressure value. More particularly, the brake mechanism includes a spring-biased piston that is adapted to cooperate with mating surfaces on the spool member to releasably lock the spool member to the housing and wherein the piston overcomes a force of at least one spring to release the lock when a predetermined hydraulic pressure is present in a space between one end surface of the stop member and the vane. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]    The foregoing features, objects and advantages of the invention will become apparent to those skilled in the art from the detailed description of a preferred embodiment, especially when considered in conjunction with the accompanying drawings in which like numerals in the several views refer to corresponding parts. 
           [0013]      FIG. 1  is a perspective view of the rotary actuator assembly comprising a preferred embodiment of the present invention; 
           [0014]      FIG. 2  is a view showing the rotary actuator partially sectioned and the housing broken away; 
           [0015]      FIG. 3  is a view showing the rotary actuator assembly with the housing eliminated to reveal the inner working parts; 
           [0016]      FIG. 4  is a view of the assembly with both the housing and the annular brake piston removed; 
           [0017]      FIG. 5  is a vertical cross-section taken along the lines  5 - 5  in  FIG. 1 ; and 
           [0018]      FIG. 6  is a perspective, cross-sectioned view taken the line  6 - 6  in  FIG. 5 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    Referring first to  FIG. 1 , there is shown a perspective view of the rotary actuator assembly comprising a preferred embodiment of the present invention. It is indicated generally by numeral  10  and is seen to comprise a generally cylindrical housing  12  in which is journaled a spool member  14 . That is to say, the spool member  14  is rotationally mounted within the housing  12 , and visible on the upper surface  16  of the spool member is a central bore  17  and a plurality of threaded bores  18  arranged in a circular pattern by which the actuator assembly can be attached to one of a frame or load. The central bore  17  reduces the weight of the structure when foot mounted and also allows straddle mounting by inserting a support shaft through this bore. In the case of straddle mounting, the housing  12  is equipped with mounting feet (not shown) to secure it to a stationary member. 
         [0020]    Bolted to the lower edge of the housing  12  is a cap member  20  and it, too, includes a pattern of threaded bolt holes allowing the rotary actuator assembly  10  to be attached to the other of the frame or load. 
         [0021]    Referring next to  FIG. 2 , which shows the rotary actuator  10  partially sectioned and the housing broken away to reveal the inner construction of the assembly, it can be seen that the housing  12  has a stepped interior wall proximate its upper edge for rotationally supporting the spool member  14  thereon. Specifically, the perimeter edge  22  of the spool member overlays an upper edge  24  of the housing with a moisture seal  26  therebetween. A bushing  28  is inserted between mating surfaces of the housing and the spool member for centering the spool member within the confines of the housing. The spool member  14  rides upon a thrust bearing  30  that is disposed in a space between mating shoulders on the spool member  14  and the housing  12 . 
         [0022]    The spool member  14  includes an annular recess  32  and affixed to the wall of this recess by socket head cap screws  36  is a wedge-shaped vane  34 . O-ring seals, as at  38 , are provided between the heads of the cap screws and the vane to prevent leakage of hydraulic fluid along the length of the fastening bolts. Likewise, a seal and O-ring combination is disposed between the rotatable spool member  14  and the inner wall of the housing  12  adjacent the outer vertical edge of the vane  34 , again to prevent hydraulic fluid under high pressure from escaping the confines of the spool recess  32  during operation of the hydraulic actuator  10 . 
         [0023]    With continued reference to  FIG. 2 , the spool member  14  has a frustoconical zone  42  for accommodating an internal brake piston  44  which rests upon one or more disk springs  46 . Without limitation, the disk springs may be annular in shape and can be stacked on a series of circumferentially spaced dowel pins, as at  48 , as will be explained in greater detail in connection with  FIGS. 3 and 4 . The annular brake member  44  has an outer annular groove about its perimeter and fitted into this groove is a cup seal  50 . Likewise, an inner diameter of the annular brake  44  also has a seal groove occupied by a further cup seal  52 . 
         [0024]    The housing cap  20  is shown as bolted to the housing  12  by a series of circumferentially spaced socket head cap screws, several of which are identified in  FIG. 2  by numeral  54 . Formed inwardly from the bottom surface of the housing cap  20  is an annular, concentric recess into which is affixed an annular spool cap  56 . By providing this spool cap, during assembly of the rotary actuator, a bushing  58  and a thrush washer  60  may be inserted prior to attachment of the spool cap  56  to facilitate centering of the spool member  14  and its ability to rotate within the housing. 
         [0025]    In the broken-away section shown in  FIG. 2 , there can be seen an arcuate stop  62 .  FIG. 3  illustrates the rotary actuator assembly with the housing  12  removed and, from this view, it can be seen that the stop  62  spans a predetermined arc. The arc of the stop  62  varies from model to model depending upon the desired angle of rotation; hence, any angle of rotation can be achieved up to 200°. The central opening  64  in the stop performs no function, except to reduce the overall weight of the device. Also visible in  FIG. 3  are hydraulic fluid inlet/outlet ports  66  and  68  proximate the end faces of the stop  62 . As explained in greater detail below, these inlet/outlet ports are connected by internal bores to ports, as at  70  in  FIG. 2 , formed on the exposed edge aces of the stop  62 . 
         [0026]      FIG. 4  is a view of the assembly with both the housing and the annular brake piston  44  removed to better illustrate one type of biasing spring arrangement that may be used in implementing the preferred embodiment. The stacks of Bellville springs are circumferentially equally spaced about the spool  14  on dowel pins  48  that project outward from bores formed on the upper face of housing cap  20 . Other types of biasing springs, e.g., coil, wave compressible polymer, etc., may be used to supply force to engage the brake, but the Bellville type spring has been used in this illustration. 
         [0027]    Also visible in  FIG. 4  is the seal groove for the vane and stop seal  92 . The seal has a rectangular shape and seals the end periphery of the vane and stop on each end. This prevents leakage across the vane cavity. 
         [0028]    As seen in the vertical cross-sectional view of  FIG. 5 , the annular piston brake  44  rests upon the springs  46  and, thus, is normally biased upward so that the frustoconically shaped surfaces of the spool  14  and the brake piston  44  frictionally engage one another to lock the spool against rotation of the spool  14  relative to the housing  12 . 
         [0029]    With continued reference to  FIG. 5 , it will be note that a hydraulic fluid inlet port  71  extends through the housing wall and leads to a gap or space above the top surfaces of the annular brake piston  44 . Hence, when hydraulic fluid under a predetermined high pressure is forced through the inlet port  71 , it will act upon the exposed upper surfaces of the piston brake, forcing it downward against the counterforce afforded by the springs  46 . With the springs thereby compressed, the frustoconical surfaces of the spool and brake piston no longer engage one another and the spool can be made to rotate relative to the stationary housing  12 . However, when the hydraulic fluid pressure at the port  71  is relieved, the springs  46  again urge the brake piston upward to again lock the spool relative to the housing. Thus, upon an intended or unintended loss of hydraulic pressure, the brake is applied to prevent rotation. Also evident in  FIG. 5  are the radial seals  40  and  42  that prevent leakage from the vane cavity to exterior parts of the actuator. 
         [0030]      FIG. 6  shows a perspective, cross-sectioned view taken along the line  6 - 6  in  FIG. 5 . In this view, it can be seen that the inlet/outlet port  66  through the housing  12  leads to a passageway  72  formed in the stop member and out the port  70  formed through a faceplate  74  that is affixed to the stop  62  by flathead cap screws, as at  76 . Faceplate  74  also retains the end periphery seals (D-ring) from the stop and vane. In a similar fashion, the inlet/outlet port  68  formed in the housing  12  leads to a channel  78  formed near the opposite end surface of the stop  62 , and thence through a bore  80  in the stop end plate  82  to a variable chamber  84  formed between the stop  62  and the vane  34 . It will be seen that when hydraulic fluid under pressure is injected through the port  68 , it will exit the bore  80 , filling the chamber  84  and urging the vane in a clockwise direction, when viewed in  FIG. 6 . However, when the hydraulic fluid, under pressure, is injected into the inlet/outlet port  66 , it will exit the bore  70  to fill the chamber  86  to force the vane  34  in a counterclockwise direction until the vane  34  hits the stop  62 . As the vane  34  moves in the counterclockwise direction, it will bleed the hydraulic fluid back through the bore  80 , the passage  78  and the inlet/outlet port  68 , returning the hydraulic fluid to nominal tank pressure. 
         [0031]    Thus, when it is desired to rotate the spool  14  relative to the housing  12  and thereby swing a load (not shown) relative to a stationary frame (also not shown), hydraulic fluid pressure is first used to disengage the braking mechanism in the manner already described and to rotate the spool to a desired angular position within the housing. As soon as the hydraulic pressure is relieved, the springs  46  function to re-engage the brake piston with the spool to lock the spool at its set position. 
         [0032]    To prevent unwanted leakage through the interface between the spool  14  and the stop  62 , as well as between the stop  62  and the housing  12  to which it is fastened, an elastomeric D-ring  91  is interposed in the grooves  92 , as seen in  FIGS. 3 and 6 . 
         [0033]    It can be seen, then, that there is provided by the present invention a rotary actuator having a fail-safe locking feature that precludes rotation of a load relative to a fixed frame whenever hydraulic pressure is not being applied to swing a load relative to its fixed frame. The rotary actuator of the present invention also incorporates unique sealing structures that confine the applied hydraulic fluid to the selected one of the two variable chambers defined between the ends of the vein and the ends of the stop. It will be apparent to those skilled in the art that the invention may be used in a variety of applications as may be appropriate without departing from the scope of the invention herein claimed. Moreover, since particular operating requirements and environments, as also will be apparent to those skilled in the art, the invention is not considered to be limited to the specific embodiment chosen for the purpose of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of the invention.