Abstract:
An actuator noise reducer reduces the noise output of an HVAC actuator. The noise reducer has a spring arm with a sliding bearing surface which is pressed against a side of the rotating motor shaft. The spring arm introduces a generally radial force on the motor shaft, taking up bearing play and gently pressing the motor shaft into its bearing. A cylindrical hoop mount of the noise reducer mates with and encircles a cylindrical portion of the electrical motor adjacent the shaft for mounting the actuator noise reducer on the motor by axial sliding.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    None. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention is directed to actuators for valves and dampers, such as used in controlled heating, ventilating and air conditioning (“HVAC”) applications. Depending upon the control system being used, such HVAC actuators typically act for a relatively short period of time (a few seconds up to a minutes or two), typically running a few times (perhaps five to ten movements) a day. In the most common applications, the HVAC actuators use a small electrically powered motor which runs at many rpms, through a gear reduction unit to increase torque and reduce the angular output of the HVAC actuator so it appropriately turns the attached valve stem or damper handle. 
         [0003]    Some HVAC actuators operate in noisy environments (such as in an industrial plant) or in locations that are not sensitive to noise. Other HVAC actuators, however, are placed in office environments, in libraries, in residences or in other locations that are much more sensitive to sound and noise issues. When the HVAC actuator works to open or close the valve or damper, it can generate sound/noise which disturbs occupants of the building. Such sound/noise can be particularly disconcerting in that the person hearing the HVAC actuator often does not know what device created the sound/noise, or why the sound/noise occurred at that particular moment in time. Accordingly, HVAC actuators should work as quietly as possible. In general, the sound generated by a working HVAC actuator has been viewed as a necessary evil, with the only viable options being to either add a more expensive motor in the HVAC actuator design (leading to a more expensive product), or to have the installer sound insulate around the HVAC actuator or around the motor within the HVAC actuator. Both options increase the total expense of the HVAC actuator. Better solutions are needed. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    The present invention is an actuator noise reducer, a motor with an actuator noise reducer thereon, and an actuator having an actuator noise reducer therein. The actuator noise reducer has a spring arm with a sliding bearing surface which is pressed against a side of the rotating motor shaft. The spring arm introduces a generally radial force on the motor shaft, taking up bearing play and gently pressing the motor shaft into its bearing. In the preferred embodiment, the actuator noise reducer includes a cylindrical hoop mount which mates with and encircles a cylindrical portion of the electrical motor adjacent the shaft for mounting the actuator noise reducer on the motor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a perspective assembly view of the actuator noise reducer of the present invention relative to the motor for which the actuator noise reducer was designed. 
           [0006]      FIG. 2  is a perspective view with the actuator noise reducer on the motor. 
           [0007]      FIG. 3  is a plan view of the actuator noise reducer of  FIGS. 1 and 2 . 
           [0008]      FIG. 4  is a side view of the actuator noise reducer of  FIGS. 1-3 . 
           [0009]      FIG. 5  is cross-sectional view of the actuator noise reducer taken along lines  5 - 5  of  FIG. 3 . 
           [0010]      FIG. 6  is a top plan view of an actuator using the actuator noise reducer of the present invention. 
           [0011]      FIG. 7  is a bottom plan view of the actuator of  FIG. 6  with the bottom plate removed to show the gear train of the actuator. 
           [0012]      FIG. 8  is a cross-sectional view of the actuator taken along lines  8 - 8  of  FIG. 6 . 
           [0013]      FIG. 9  is a cross-sectional view of the actuator taken along lines  9 - 9  of  FIG. 6 . 
           [0014]      FIG. 10  is an enlargement of a portion of  FIG. 9 . 
       
    
    
       [0015]    While the above-identified drawing figures set forth a preferred embodiment, other embodiments of the present invention are also contemplated, some of which are noted in the discussion. In all cases, this disclosure presents the illustrated embodiments of the present invention by way of representation and not limitation. Numerous other minor modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention. 
       DETAILED DESCRIPTION 
       [0016]    The operation of the noise reducer  10  of the present invention can be understood with reference to  FIGS. 1-5 , which most clearly show the noise reducer  10 . In this case, the noise reducer  10  has been specifically designed to mate and work with a known motor  12  used in an HVAC actuator  14 . In typical HVAC actuators (and in the preferred embodiment), the motor  12  runs at speeds in excess of 100 rpms, and usually at speeds of 1000 rpms or more. This relatively fast motor output speed is then geared down to increase torque and reduce the angular output of the HVAC actuator  14 . For valve applications, the maximum stroke of the actuator is several turns (say, 1080° or less), and more commonly with a maximum stroke of about 90° . With damper applications, the maximum stroke of the actuator is commonly 180° or less. The HVAC actuators typically have a peak torque output of 10 in-lbs or more to up to about 400 in-lbs, such as low torque models rated at about 40 in-lbs and high torque models rated at about 320 in-lbs. 
         [0017]    The depicted motor  12  is a long shaft DC motor rated at 24 VDC, commercially available from Douglas International, Inc. of Geneva, Ill. as model no. KE588. It has a rated load of 1.0 in-oz (0.06 in-lbs, or 72 g-cm), drawing about 130 mA and running at 2100±250 rpm at rated load. At no load, the preferred motor  12  draws about 15 mA and runs at 3250±350 rpm. 
         [0018]    The housing  16  of the motor  12  is generally cylindrical, with an outer diameter of about 1.4 inches (36 mm) and a length of about 1 inch (26 mm). Positive and negative electrical terminals  18  project off one end of the housing  16  opposite a motor shaft  20 . As well known in the HVAC actuator and motor arts, application of an appropriate electric current to the two electrical terminals  18  causes rotation of the shaft  20  by a rotor/stator combination (not shown) interior to the housing  16 . The shaft  20  is rotationally supported by bearings or bushings (not shown) which are also interior to the motor housing  16 . In this particular motor  12 , an end plate  22  of the housing  16  includes a cylindrical extension  24  around the bearing/bushing, and has several threaded mounting holes  26  in the end plate  22 . The cylindrical extension  24  projects just over 0.1 inches (about 3 mm) from the rest of the end plate  22 , with an outer diameter of about 0.4 inches (10 mm). While the noise reducer  10  of the preferred embodiment is specifically designed to mate with the size and shape of this particular motor  12 , the noise reducer can be alternatively designed to mate with motors having widely varying external shapes. 
         [0019]    The shaft could be rectangular or hexagonal or otherwise shaped with one or more flats to mate into a gear, but in the preferred motor  12  the shaft  20  is cylindrical. The shaft  20  has a thickness appropriate for the torque being transferred, such as typically with a diameter in the range of 0.05 to 0.25 inches (1 to 6 mm). The shaft  20  of the preferred motor  12  has a diameter of less than 0.1 inches (about 2 mm), extending for a length of about 0.3 inches (about 7 mm) beyond the cylindrical extension  24 . 
         [0020]    While this motor  12  is relatively low cost and reliable for its intended use in the HVAC actuator  14 , it generates more noise than desired while running. The present invention involves the discovery that the noise output of the motor  12  can be reduced by placing a sideways force on the shaft  20  as it projects beyond the cylindrical extension  24 . In general terms, most designers using motors would try to avoid such a sideways force (i.e, a force in one radial direction) on the shaft  20  as detrimental to motor performance. Specifically, the sideways force on the shaft  20  tends to increase wear in the bearings/bushings, reduces the torque output of the motor  12  due to unnecessary drag, and tends to cause misalignment of the rotor/shaft relative to the stator within the housing  16 . For an HVAC actuator, however, these downsides are insignificant. With the HVAC actuator  14  having a total run time of only a few minutes per day, bearing or bushing wear is seldom a significant contributing cause for motor failure. Further, with a properly designed noise reducer  10 , the trade-off of lower torque is well worth the reduction in sound output of the HVAC actuator  14  while running. 
         [0021]    The sideways force is placed onto the shaft  20  by a spring arm  28 . The spring arm  28  extends from a hoop section  30  of the noise reducer  10  which mounts the noise reducer  10  relative to the motor  12  and/or actuator  14 . The spring arm  28  has a bearing surface  32  on its free distal end which rides on the cylindrical side surface of the shaft  20  at a location just past the end of the cylindrical extension  24 . While numerous designs of spring arms could be used, the preferred spring arm  28  includes two fold locations  34  separating two relatively straight lengths  36  of the spring arm  28 . Most of the deflection of the spring arm  28  is provided by bending of the material at these two fold locations  34 . In the preferred embodiment, the spring arm  28  is molded to be about 0.02 inches (0.5 mm) thick, with the width of the spring arm  28  ranging between about 0.04 and 0.05 inches (1-1.2 mm). Numerous other geometries for the spring arm could alternatively be used. 
         [0022]    The amount of deflection of the spring arm  28  is designed based upon the magnitude of the spring force desired and the geometrical configuration of the spring arm  28  to achieve that magnitude of spring force. For many configurations, the desired sideways spring force is achieved by a deflection of the bearing surface  32  by a distance within a range of 0.004 to 0.2 inches (0.1 to 5 mm). In the preferred design, the unbiased position of the bearing surface  32  coincides with the shaft axis. Thus, placement of the noise reducer  10  onto the motor  12  requires deflecting the bearing surface  32  of the spring arm  28  by an amount equal to the radius of the shaft  20 , which for the preferred motor  12  is about 0.04 inches (1 mm). 
         [0023]    The spring constant for the spring arm  28  is also designed based upon the magnitude of the spring force desired and the geometrical configuration of the spring arm  28  to achieve that magnitude of spring force, and further considering the tolerances of the motor  12  and placement of the noise reducer  10 . In general, the desired spring force can be achieved with springs having a spring constant within a range of 0.5 to 500 pounds per inch. 
         [0024]    The spring arm  28  provides a sideways force on the shaft  20  which is appropriate for the particular motor  12  to reduce the noise output of the motor  12 , and can be readily determined by placing a range of different forces on the motor  12  and seeing how noise output is reduced relative to the reduction in torque output. In HVAC actuators, the sideways force that the actuator noise reducer  10  places on the motor shaft  20  is generally within a range of 0.1 to 5 pounds to result in the desired noise reduction. With the preferred motor  12 , a sideways force within the range of 0.3 to 1.2 pounds has been found to adequately reduce motor noise. With the geometrical configuration and size of the preferred embodiment, forming the noise reducer  10  of DELRIN (Unfilled Acetal) results in a sideways force of about 0.38 lbs, forming the noise reducer  10  of LUBRICOMP (Nylon 6/6 w/10% aramid fibers &amp; 10% PTFE) results in a sideways force of about 0.40 lbs, and forming the noise reducer  10  of ULTRAMID (35% Glass filled Nylon 6/6) results in a sideways spring force of about 1.2 lbs. That is, with a deflection of 0.04 inches (1 mm), the preferred shape results in spring constants of about 9 pounds per inch (DELRIN and LUBRICOMP) to about 30 pounds per inch (ULTRAMID). By molding the noise reducer  10  out of a polymer material, the noise reducer  10  can be easily formed at low cost, while providing the design flexibility needed to mate with various motors used in HVAC actuators and achieve desired spring forces on the motor shafts. 
         [0025]    The amount of noise reduction achieved by the noise reducer  10  should be audibly perceptible, such as a reduction of at least 3 dB, and more preferably a reduction of at least 5 dB. The preferred embodiment reduces the noise output of the actuator  14  by about 10 to 15 dB or more. While various causes internal to the motor  12  may contribute to the sound output of the motor  12 , it is believed that the noise reducer  10  significantly takes up about 0.0002 to 0.0003 inches (0.005 to 0.008 mm) of bearing play (difference between motor shaft diameter and motor bearing diameter). 
         [0026]    The sideways force does introduce friction and thereby reduces the efficiency of the motor  12  slightly, but not overly so. For instance, the noise reducer  10  may reduce the no-load running speed of the motor  12  by an amount within the range of 0.5 to 20%, and more preferably within the range of 1 to 10%. Measurements were taken of the reduction of no-load running speed of the motor  12  with the preferred embodiment as follows. Without the noise reducer  10 , a sampled motor  12  ran at 3113 rpm in the clockwise direction and at 3068 rpm in the counterclockwise direction. A preferred noise reducer  10  molded of DELRIN reduced these speeds to 3000 rpm (3.6% reduction) in the clockwise direction and to 2955 rpm (3.7% reduction) in the counterclockwise direction. A preferred noise reducer  10  molded of LUBRICOMP reduced these speeds to 3071 rpm (1.4% reduction) in the clockwise direction and to 3023 rpm (1.5% reduction) in the counterclockwise direction. A preferred noise reducer  10  molded of ULTRAMID reduced these speeds to 2894 rpm (7.0% reduction) in the clockwise direction and to 2839 rpm (7.5% reduction) in the counterclockwise direction. 
         [0027]    The cylindrical extension  24  provides a convenient location for attachment of the noise reducer  10  of the present invention. The noise reducer  10  includes a peripheral hoop  30  of the same size and shape as the end plate extension  24 , and the peripheral hoop  30  of the noise reducer  10  is used to secure the noise reducer  10  into position relative to the motor  12 . In this case, because the end plate extension  24  is cylindrical, the peripheral hoop  30  is also cylindrical. The hoop  30  encircles the shaft axis, such that the force provided onto the shaft  20  by the spring arm  28  is transmitted through the hoop  30  directly to the motor housing  16 . Due to the shape of the housing  16 , the hoop  30  can be slid axially onto the cylindrical extension  24  to conveniently attach the noise reducer  10  to the motor  12  with a friction fit. The peripheral hoop  30  is tight enough and has enough surface contact with the cylindrical extension  24  that friction between the peripheral hoop  30  and the cylindrical extension  24  prevents the noise reducer  10  from rotating with the shaft  20 . A flat  38  may be provided in one side of the peripheral hoop  30  so the noise reducer  10  better mates with the housing  40  of the actuator  14 . The flat  38  can also be used to prevent rotation of the noise reducer  10  with the shaft  20 . Alternatively, the noise reducer  10  could attach to the mounting holes  26  provided in the end plate  22  of the housing  16 , or could attach to the outer cylindrical surface of the motor housing  16 , or could attach to the motor housing  16  in another way. As another alternative, the noise reducer could attach to other structure within the actuator  14  (shown in  FIGS. 6-10 ) separate from the motor  12 , i.e., such that the noise reducer didn&#39;t directly attach to the motor  12  at all. For instance, the noise reducer could be formed as part of the actuator housing  40 , or be attached to the actuator housing  40  or the motor  12  with one or more fasteners such as screws (not shown) or with adhesive. By having the hoop section  30  slide axially onto the cylindrical extension  24  of the motor housing  16 , a very consistent fit is achieved for placement of the noise reducer  10  onto the motor  12 , so the designed spring force is easily achieved within tolerances during production. 
         [0028]      FIGS. 6-10  depict an actuator  14  using the noise reducer  10  of the present invention. The actuator  14  largely consists of a housing  40  enclosing various electronic components  42 , with one or more wiring openings  44 . An output section  46  can have any of numerous shapes and designs to mate with a damper or valve, with the depicted actuator  14  having a U-bolt attachment  46  which can be tightened around a stem of a valve or a handle of a damper (not shown). The particular actuator  14  depicted is similar to a model MEP-4872 actuator commercially available from KMC Controls of New Paris, Ind., which is rated at 80 in-lb of torque. The motor  12  is one of the components mounted within the housing  40 , with a gear train  48  coupling the motor shaft  20  to the U-bolt attachment  46 . In most HVAC actuators, the gear train  48  will provide a gear ratio to 1000 to 1 or more, such that the motor  12  turns the output shaft connector  46  through its total travel in a time period within the range of 5 seconds to 5 minutes. In this instance, the gear train  48  includes 6 gears, providing a total gear ratio of about 2700 to 1. The 2700 to 1 gear ratio causes the motor  12  running at 2100 rpm to rotate the U-bolt output  46  a full stroke 90° in about 19 seconds, while at no-load the motor  12  running at 3250 rpm will rotate the U-bolt output  46  a full stroke 90° in about 12.5 seconds. If the noise reducer  10  reduces the running speed of the motor  12  by less than 10%, then the additional run time for full stroke travel introduced by the noise reducer  10  is less than 2 seconds. 
         [0029]    If desired, the gear train  48  can be formed with all plastic gears, or alternatively a metal gear can be used on the final gear stage(s) to withstand increased torque. While different gear trains can be used to produce different torque ratings, in the preferred embodiment different torque ratings are achieved using the same gear train  48  with the use of a magnetic hysteresis clutch  50 . This clutch  50  consists of a magnet  52  pressed onto the motor shaft  20  that drives a plastic ring cup  54  containing a rotor ring (rolled strip of hysteresis metal). As the shaft  20 /magnet  52  rotates, the rotor ring/ring cup  54  rotates with the magnet  52  until a predetermined slip torque is reached. At this point the shaft  20 /magnet  52  continues to rotate and the ring cup  54  stalls out. The slip torque can be varied by changing the strength of the magnet  52 , by modifying the air gap between the magnet  52  and the rotor ring  54 , or by changing the volume of the rotor ring material. Assuming a 93% efficient gear train  48 , the rated output torque/nominal output stall torque/nominal clutch torque of the three torque ranges are as follows: 25 in-lb/45 in-lb (clutch slips at 0.018 in-lb), 45 in-lb/65 in-lb (clutch slips at 0.025 in-lb), and 90 in-lb/112 in-lb (clutch slips at 0.044 in-lb). 
         [0030]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.