Abstract:
A rotational speed control device maintains a shaft rotation speed. The device includes a housing containing a viscous fluid and a shaft disposed in the housing and rotatable relative to the housing. A rotor is coupled with the shaft for rotation in the viscous fluid. The rotor is axially displaceable along the shaft between a low-shear position and a high-shear position. A spring mechanism is disposed in the housing and biases the rotor toward the low-shear position. The rotor may be designed to cooperate with the housing or other nonrotating features within the housing to vary a shear gap according to the axial position of the rotor. The rotor, housing and spring mechanism can be designed to cooperate to create large changes in braking torque in response to small changes in shaft rotational speed. This allows the rotation speed to be controlled within a relatively narrow range.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/103,168, filed Jan. 14, 2015, the entire content of which is herein incorporated by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    (Not Applicable) 
       BACKGROUND OF THE INVENTION 
       [0003]    It is desirable to maintain a relatively constant speed of rotation of an irrigation sprinkler regardless of nozzle size or pressure (i.e., mass flow rate and fluid velocity). This invention results in a large increase in braking torque for a small increase in rotational speed and therefore minimizes the change in rotational speed of the irrigation sprinkler when nozzle size or pressure is changed. 
         [0004]    For many years, a braking system has been in use that utilizes a rotor that is immersed in a viscous fluid. The rotor is connected to a shaft which transmits the energy of the rotating sprinkler into the viscous-braking mechanism. The rotor, viscous fluid and a portion of the shaft are contained within a sealed housing. As the shaft and rotor rotate, the viscous fluid is sheared between the rotor and the housing. As the shear rate increases, the braking torque that retards the shaft rotation also increases. As a matter of operation, the shear rate increases due to an increase in the rotational speed of the shaft and therefore the surface speed of the rotor. As a matter of design, the shear rate can be increased by decreasing the gap between the rotor and the housing. 
         [0005]    It is desirable to avoid requiring the shaft to move axially in and out of the housing. Axial movement can drag water and other contaminants into the seal and thereby cause water intrusion and/or excessive wear. Additionally, as the shaft moves into the housing, it pressurizes the fluid chamber, which can cause excess seal friction and seal wear unless an expansion chamber is added. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    In some embodiments of this invention, the gap between the rotor and the housing is changed automatically in response to changes in rotational speed of the shaft. The rotor is attached to the shaft in a manner that causes it to rotate with the shaft but allows it to move axially relative to the shaft. The rotor is designed with an impeller-like feature to create an axial force when it is rotated in the viscous fluid. The magnitude of the axial force is proportional to the rotational speed of the rotor. A spring mechanism is located within the housing in such a way as to resist the axial force of the rotor. The axial force of the rotor compresses the spring mechanism until the spring force matches the axial force being generated by the rotation of the shaft and rotor. These balancing forces are used to determine the axial position of the rotor within the housing. 
         [0007]    When the rotational speed of the input shaft changes due to changing pressures or nozzle size of the sprinkler, the rotor moves to a new axial position. The rotor is designed to cooperate with the housing or other nonrotating features within the housing to vary the shear gap in response to the axial position of the rotor. The rotor, housing and spring mechanism can be designed to cooperate to create large changes in braking torque in response to small changes in rotational speed of the input shaft. This allows the sprinkler rotation speed to be controlled within a relatively narrow range. 
         [0008]    Alternatively, the structure may be configured to use vanes to create radial movement rather than axial movement. Other alternate embodiments use mating threads working against either compression or torsional springs to create axial movement. Another alternate embodiment uses mechanical friction in addition to viscous fluid shear to create the braking torque. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    These and other aspects and advantages will be described in detail with reference to the accompanying drawings, in which: 
           [0010]      FIG. 1  shows an exemplary rotational speed control device in a low-braking stage; 
           [0011]      FIG. 2  shows the rotational speed control device of  FIG. 1  transitioning between the low-braking stage and the high-braking stage; 
           [0012]      FIG. 3  shows the rotor; 
           [0013]      FIG. 4  shows an alternative embodiment of the rotational speed control device with a modified rotor; 
           [0014]      FIG. 5  shows the embodiment of  FIG. 4  in an intermediate-braking position; 
           [0015]      FIG. 6  shows the rotor for the embodiment of  FIGS. 4 and 5 ; 
           [0016]      FIG. 7  is a sectional view of an alternative embodiment; 
           [0017]      FIG. 8  is a sectional view of the  FIG. 7  embodiment with the rotor transitioning from a low-braking position to a high-braking position; 
           [0018]      FIG. 9  is a sectional view of an alternative embodiment utilizing a disk-shaped rotor; 
           [0019]      FIG. 10  is a sectional view of the embodiment in  FIG. 9  in a high-braking position; 
           [0020]      FIG. 11  is a sectional view of an alternative embodiment showing a 3-stage device with added sheer area in the minimum braking position; 
           [0021]      FIG. 12  is a sectional view of the  FIG. 11  embodiment in a maximum braking position; 
           [0022]      FIG. 13  is a sectional view of the  FIG. 11  embodiment including a drive control band; 
           [0023]      FIG. 14  is a graph showing typical compensating and noncompensating viscous speed control performance; 
           [0024]      FIGS. 15 and 16  show the rotational speed control device as part of an industrial sprinkler; 
           [0025]      FIG. 17  is a sectional view of an alternative embodiment utilizing nested cylinders; 
           [0026]      FIG. 18  shows the shaft and a threaded hub for the  FIG. 17  embodiment; 
           [0027]      FIG. 19  is a detailed view of the rotor for the  FIG. 17  embodiment; 
           [0028]      FIG. 20  shows the rotor in the  FIG. 17  embodiment approaching a maximum torque position; 
           [0029]      FIG. 21  is an upper perspective view of the brake assembly of an alternative embodiment; 
           [0030]      FIG. 22  is a vertical section view of  FIG. 21  showing the hub and brake shoes; 
           [0031]      FIGS. 23 and 24  show a lower view of the  FIG. 21  assembly with the housing removed; 
           [0032]      FIG. 25  is an upper perspective view of an alternative brake assembly; 
           [0033]      FIGS. 26 and 27  are sectional views of the  FIG. 25  embodiment; 
           [0034]      FIG. 28  is a perspective view of the rotor in the  FIG. 25  embodiment; 
           [0035]      FIG. 29  is a side view of an alternative embodiment installed in an exemplary rotator sprinkler; 
           [0036]      FIG. 30  is a sectional view of  FIG. 29 ; 
           [0037]      FIG. 31  is a sectional view of the brake assembly in the  FIG. 29  embodiment; 
           [0038]      FIG. 32  is a sectional view of the  FIG. 29  embodiment with the rotor in a high-braking position; 
           [0039]      FIG. 33  is a perspective view of the housing in the  FIG. 29  embodiment; 
           [0040]      FIGS. 34-36  are perspective views of the rotor in the  FIG. 29  embodiment; 
           [0041]      FIG. 37  is a sectional view of an alternative embodiment in an at-rest position and low-speed position; 
           [0042]      FIG. 38  is a sectional view of the  FIG. 37  embodiment in a high-braking position; 
           [0043]      FIG. 39  is a perspective view of the threaded hub and torsion spring in the  FIG. 37  embodiment; 
           [0044]      FIGS. 40 and 41  show the rotor of the  FIG. 37  embodiment; and 
           [0045]      FIG. 42  is a perspective view of the torsion spring in the  FIG. 37  embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0046]    The figures show several embodiments of a viscous rotational speed control device  10 . With reference to  FIG. 1 , a rotor  12  is rotatable with a shaft  14  in a housing  16 . The housing  16  is filled with a viscous fluid such as high-viscosity silicone fluid or the like. The housing  16  is closed at a bottom end and includes a recess or channel  18  for receiving the shaft  14 . A seal  20  secured with a seal retainer  22  contains the viscous fluid within the housing  16 . 
         [0047]    A retaining ring  30  and a bearing retainer  28  are used to axially locate the ball bearing on the shaft  14 . A lower bearing support  26  and an upper bearing support  24  cooperate to axially and radially locate the shaft bearing assembly in the housing  16 .  FIGS. 1-10 and 13  utilize a ball bearing to support the axial and radial load that the water imparts on the shaft  14 . The axial load is transmitted to the housing  16  via the lower bearing support  26 . 
         [0048]    The rotor  12  includes a braking section  32  and an impeller  34 . The clearance between the braking section  32  and an inner wall of the housing  16  is directly related to the amount of braking. In section A shown in  FIG. 1 , the clearance between the braking section  32  of the rotor and the inner wall of the housing  16  is relatively large for low-braking. The inner wall of the housing  16  includes a step  36  that narrows the clearance between the braking section  32  of the rotor  12  and the inner wall of the housing  16 . The smaller clearance provides for greater braking. 
         [0049]    A spring mechanism such as a balancing spring  38  acts on the rotor  12  and urges the rotor  12  toward the high clearance low-braking position shown in  FIG. 1 . The balancing spring is secured via a spring retainer  40 . As the shaft  14  and rotor  12  are rotated, the impeller  34  drives the rotor axially against the force of the spring  38 . The clearance between the impeller  34  and the inside wall of the housing  16  is relatively small to enable the impeller to more effectively drive the axial position of the rotor  12 . The axial force of the rotor  12  compresses the spring  38  until the spring force matches the axial force being generated by the rotation of the shaft  14  and rotor  12 . When the rotational speed of the input shaft  14  changes due to changing pressures or nozzle size of the sprinkler, the rotor  12  moves to a new axial position. The spring mechanism may comprise any suitable structure for providing the bias, for example, opposing magnets or equivalent structure. 
         [0050]      FIG. 2  shows the rotor  12  displaced axially by an increase in the rotationally developed axial force. The rotor  12  is displaced such that at least a portion of the braking section  32  is disposed adjacent the small clearance section B of the inner wall of the housing  16 . By virtue of the smaller clearance, a greater braking resistance is provided.  FIG. 3  is an isolated view of the rotor  12 . 
         [0051]      FIGS. 4 and 5  show an alternative embodiment. In this embodiment, the rotor  112  is generally cylindrical and is provided with screw thread slots  134  that define the impeller for driving an axial position of the rotor  112 . The inner wall of the housing  16  includes the step  36  such that with slower rotation, a larger portion of the rotor  112  is positioned adjacent the large clearance section A of the housing for lower braking. In the smaller clearance section B, the screw impeller/screw thread slots  134  can more effectively drive, and the smaller clearance creates relatively high-shear braking on the thread major diameter for higher braking at higher rotation speeds. With reference to  FIG. 5 , as the screw impeller  134  drives deeper, more of its major diameter is in the low clearance section B, which creates more shear area and therefore, more braking. In  FIGS. 4 and 5 , the screw thread has a relatively short pitch with a broad thread crest. The shearing action that creates the braking is done primarily between the thread crest (major diameter) and the housing  16 .  FIGS. 4 and 5  show the rotor having a variable pitch screw thread with the pitch getting greater at the top. This is to create progressively wider thread crests and more area subject to the high shear that occurs in the smaller clearance section B. This style of rotor may have a variable pitch as shown or a constant pitch depending on the desired performance.  FIG. 6  is an isolated view of the rotor  112 . 
         [0052]      FIGS. 7 and 8  show an alternative design for varying the shear and braking based on the axial position of the rotor  212 . In this embodiment, the braking portion  232  of the rotor  212  is part conical-shaped, and the low clearance section B in the housing  16  is correspondingly conical-shaped.  FIG. 7  shows the rotor  212  in the low-shear/low-braking position, and  FIG. 8  shows the rotor  212  at least partially in the high-shear/high-braking position. Note that the shear gap  213  gets smaller as the axial position of the rotor  212  is displaced against a force of the spring  38  by the impeller  34  due to increased rotation speeds. 
         [0053]      FIGS. 9 and 10  show yet another alternative embodiment where the housing includes a shoulder  313 , and the braking portion  332  of the rotor  312  is spaced from the shoulder  312  by a variable shear gap C. As the axial position of the rotor  312  is driven by the impeller  34 , the shear gap C is reduced as shown in  FIG. 10  for higher shear and higher braking. 
         [0054]      FIGS. 11-13  show an embodiment that not only changes the shear gap, but also adds additional shear area. The rotor  412  includes a circular slot  413  that engages a standing rib or circular ridge  414  formed in the housing  16 . The ridge  414  provides added shear area when engaged by the rotor  412 . In  FIG. 13 , the ridge  414 ′ forms parts of a drive control band  420  inserted between the housing  16  and the rotor  412 . The drive control band  420  keeps the length of the screw portion/impeller  34  of the rotor  412  that is engaged in the tight diameter constant and gives better control of the rotor response. 
         [0055]      FIG. 14  is a typical performance graph that illustrates the performance difference between a conventional viscous brake and this device. 
         [0056]      FIGS. 15 and 16  show the device  10  as part of a sprinkler. Note that the device  10  may also be employed in other forms of sprinklers including ones that would transmit torque to the device shaft via a gear train. 
         [0057]      FIG. 17  shows another alternative configuration where the housing  16  is provided with a plurality of circular grooves  514  separated by a cylindrical ridge  515 . The rotor  512  includes separated cylinders  516  that are cooperable with the grooves  514  to increase or decrease the shear and braking based on an axial position of the rotor  512 . A threaded hub  522  is press fit to the shaft  14  so that it will rotate with the shaft. As it begins to rotate, the rotor  512  also rotates with the threaded hub  522 , until such time that the rotation speed becomes high enough that the viscous shear overcomes the compression spring  538 .  FIG. 18  is an isolated view of the threaded hub  522  and the shaft  14 .  FIG. 19  is an isolated view of the rotor  512 .  FIG. 20  shows the rotor  512  displaced axially from the position shown in  FIG. 17  and approaching the maximum torque position. 
         [0058]      FIGS. 21-28  show two further embodiments for viscous fluid compensating brakes. Like prior embodiments, both units are filled with a high-viscosity silicone fluid or the like. Both designs utilize a shaft that turns components that have radially expanding members. The radially expanding members expand in response to rotation speed to increase the braking torque by decreasing the viscous fluid shear gap. In the embodiment of  FIGS. 21-24 , the device is shown with a smooth outside diameter on the brake shoes  614  that interacts with a smooth inside diameter on the housing  16 . The embodiment shown in  FIGS. 25-28  utilizes labyrinth-type geometry in the area of interaction, but smooth or labyrinth could be used with both concepts. 
         [0059]      FIG. 21  is an upper perspective view of the brake assembly alone.  FIG. 22  is a vertical section view of  FIG. 21  showing the hub  612  and brake shoes  614 .  FIGS. 23 and 24  show a lower view of the assembly with the housing removed. The brake shoes  614  are in the minimum torque position, being biased there by integral springs  616 . The minimum torque position shown is the position of the shoes  614  when the unit is at rest or when turning very slowly. The leading edges of the shoes are shaped such that as rotation speed increases, the shoes  614  will pivot outward against the force of the spring  616  to decrease the fluid shear gap on the outside of the shoes  614 , thereby increasing the braking torque. The shoes  614  may be configured to press against the housing to add a mechanical friction component to the braking torque. 
         [0060]      FIG. 25  is an upper perspective view of an alternative brake assembly alone.  FIGS. 26 and 27  are vertical section views. In  FIG. 26 , the rotor  712  is in the minimum torque position (at rest or at low speed), and in  FIG. 27 , the rotor  712  is nearing the maximum torque position. The rotor  712  includes a plurality of angled propeller blades  718  at the top of the rotor  712 . As speed increases from the configuration in  FIG. 26 , the propeller blades  718  force the rotor segments outwardly, and the labyrinth segments on the rotor  712  are interacting with the labyrinth rings  720  in the housing  16  to decrease the fluid shear gap and thereby increase the braking torque. 
         [0061]      FIG. 28  is an upper perspective view of the rotor  712  alone. The rotor  712  as shown is a single piece that is molded out of a resilient plastic. The rotor could also be constructed as a multi-piece assembly if desired. 
         [0062]      FIGS. 29-36  show yet another alternative configuration of the brake assembly. In principle, it is similar to the other described embodiments. Axial motion, however, is powered with propeller-type blades rather than a screw thread, and multiple concentric rings rotate in close proximity to multiple stationary rings to create the viscous-braking action. 
         [0063]      FIG. 29  is a side view of the device  800  installed in an exemplary rotator sprinkler. Typically, sprinklers operate over a wide range of nozzle sizes and line pressure.  FIG. 30  is a vertical cross section of  FIG. 29 .  FIG. 31  shows the brake assembly  800  including the housing  16 , shaft  14  and rotor  812 . As in previous embodiments, the housing  16  is filled with a high-viscosity silicone fluid. In  FIG. 31 , the brake is at rest or turning very slowly, and the rotor  812  is in the raised or low-shear position, being biased to that position by the compression spring  38 . In the position shown in  FIG. 31 , the braking torque is at its minimum due to the relatively large clearances between the rotating and stationary members. As a torque is applied to the shaft  14 , the rotor  812  turns faster, which causes outside propeller blades  818  (and to a lesser extent, the blades connecting the rotor rings) to push the rotor  812  down against the force of the spring  38 .  FIG. 32  shows the rotor  812  in its lowermost position, which creates maximum braking by creating large areas with minimal fluid gap. Depending on the torque applied to the shaft  14 , the rotor  812  will float vertically between the minimum and maximum positions, finding an axial equilibrium between the spring load and the propeller loads. 
         [0064]      FIG. 33  is a perspective view of the housing  16  showing openings  820  cut in the inner rings to allow fluid to move from one side of the rotor to the other as the rotor moves axially.  FIGS. 34-36  are various perspective views of the rotor  812  showing the propeller blades  818 . As shown in  FIGS. 31 and 32 , the hub  822  is preferably machined out of brass square stock and press fit onto the shaft to enable transmission of torque to the rotor while also allowing axial movement of the rotor. The hub  822  also provides support for the compression spring  38 . 
         [0065]    The exemplary sprinklers of  FIGS. 29 and 30  are shown in the position used when water is supplied through a drop tube, but the same sprinkler is often used in the inverted position, for example, on top of a center pivot irrigation machine. 
         [0066]      FIGS. 37-42  show yet another alternative embodiment.  FIG. 37  is a cross section of the assembly  900  when it is in the at-rest position and low-speed position. The unit is filled with a viscous fluid. The rotor  912  is biased to the up position by a torsion spring  938 . The threaded hub  922  is press fit to the shaft  14  so that it will rotate with the shaft. As it begins to rotate, the rotor  912  also rotates with the threaded hub  922 , until such time that the rotation speed becomes high enough that the viscous shear between the rotor  912  and the housing  16  gets high enough to overcome the torsion spring  938  and the viscous shear between the rotor  912  and the threaded hub  922  to rotate the rotor relative to the threaded hub. This drives the rotor  912  down toward the position shown in  FIG. 38 . In this position, the lower end of the rotor is contacting the housing, creating mechanical frictional torque in addition to the viscous shear torque.  FIG. 39  is a detailed view of the threaded hub  922  and the torsion spring  938 .  FIGS. 40 and 41  are different views of the rotor, and  FIG. 42  is a detailed view of the torsion spring  938 . 
         [0067]    The balancing springs in the various embodiments can be replaced with opposingly oriented magnets to generate the balancing force. 
         [0068]    It should be noted that the operation of this device relies on the relative motion between the rotor and the housing. Therefore, it should be recognized that the device could be designed to have the housing rotate about a nonrotating shaft and rotor rather than the described exemplary embodiments where the shaft and rotor rotate within a stationary housing. 
         [0069]    The brake assembly can be mounted in various arrangements including ones where the shaft can be driven by a gear, rather than directly by a deflector plate, such as when used in a Big Gun Rotator™. 
         [0070]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.