Abstract:
A mass damper is carried on the frame of an reel mower by a pair of elastomeric couplers, one at each end of the mass damper. Each coupler is threadedly secured to one end of the mass damper with the coupler received in a cavity at that end of the mass damper. Each coupler is also clamped to a bracket on the frame of the reel mower. The mass damper can move relative to the frame of the reel mower by shearing the elastomeric material forming the couplers. The weight of the mass damper and the stiffness of the couplers is chosen to damp or lessen the vibration induced in the frame of the reel mower by an internal combustion engine carried on the frame of the reel mower.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to a reel mower, such as a walk greensmower, that has a vibrational excitation source, such as an internal combustion engine. More particularly, this invention relates to a mass damper movably secured to the frame of the reel mower for damping vibration caused by the vibrational excitation source.  
         BACKGROUND OF THE INVENTION  
         [0002]    Reel mowers are well known for cutting grass, often at close heights of cut. Many such reel mowers have a handle assembly that extends upwardly and rearwardly from the frame of the reel mower. This allows an operator who walks behind the reel mower during operation of the reel mower to grip and hold the handle assembly to guide and operate the reel mower. In many cases, the reel mower is self propelled by an internal combustion engine carried on the frame of the reel mower. This engine also provides power to the rotatable reel of the reel mower.  
           [0003]    The internal combustion engine provided on many reel mowers is often a single cylinder engine. Such an engine characteristically produces vibration in the frame of the reel mower as the engine operates. This vibration interferes with the precision cutting afforded by the reel mower. Some way of reducing or compensating for the vibrations induced by the engine, or such other vibrational excitation source as might be present, would be advantageous.  
         SUMMARY OF THE INVENTION  
         [0004]    One aspect of this invention relates to a reel mower having a frame supported for movement over the ground. A reel cutting unit is carried on the frame. A mass damper is attached to the frame by at least one elastomeric coupler such that the mass damper is able to move relative to the frame by deflection of the elastomeric coupler. The mass damper has a weight and the elastomeric coupler has a stiffness with the weight of the mass damper and the stiffness of the elastomeric coupler being chosen to damp or lessen vibration produced by a vibrational excitation source.  
           [0005]    Another aspect of this invention relates to a reel mower which comprises a frame supported for movement over the ground. A reel cutting unit is carried on the frame. An internal combustion engine is carried on the frame for providing power. A mass damper is attached to the frame by at least one elastomeric coupler. The mass damper is free to move relative to the frame only through shear of the coupler to damp vibration induced in the frame by the engine. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    This invention will be described hereafter in the Detailed Description, taken in conjunction with the following drawings, in which like reference numerals refer to like elements or parts throughout.  
         [0007]    [0007]FIG. 1 is a perspective view of one type of reel mower, namely of a walk greensmower, having a mass damper for reducing vibration induced in the frame of the reel mower by the internal combustion engine carried on the frame;  
         [0008]    [0008]FIG. 2 is an enlarged perspective view of a portion of the reel mower of FIG. 1, more particularly illustrating the mass damper;  
         [0009]    [0009]FIG. 3 is an enlarged perspective view of a portion of the reel mower of FIG. 1, more particularly illustrating in exploded form the mass damper and one of the elastomeric couplers that couple the mass damper to the frame of the reel mower; and  
         [0010]    [0010]FIG. 4 is an enlarged perspective view in exploded form of the mass damper and one of the elastomeric couplers that couple the mass damper to the frame of the reel mower. 
     
    
     DETAILED DESCRIPTION  
       [0011]    A reel mower is illustrated generally as  2  in FIG. 1. Reel mower  2  as shown in FIG. 1 comprises a walk greensmower  4 . However, the depiction of a walk greensmower  4  herein is for illustrative purposes and is not meant to be a representation of the only type of reel mower  2  with which this invention could be used. Reel mower  2  could also comprise a reel mower having a plurality of reel type cutting units attached to the frame of a riding vehicle, such as a reel mower known as a triplex mower. Thus, reel mower  2  could have just one reel type cutting unit  10  or a plurality of such cutting units  10 .  
         [0012]    Walk greensmower  4  includes a frame  6  that is supported for movement over the ground during operation of walk greensmower  4  by a rear traction drum  8 . A reel type cutting unit  10  is carried on the front of frame  6  for mowing grass. Cutting unit  10  is preferably carried on frame  6  in such a manner that cutting unit  10  is able to float or pivot relative to frame  6  about at one or multiple axes to allow cutting unit  10  to better follow the contours of the ground. Cutting unit  10  is supported for rolling over the ground by its own front and rear rollers  11 , with only the front roller  11  being illustrated in FIG. 1.  
         [0013]    Additional details regarding cutting unit  10  and how it is connected to frame  6  may be found in International Publication WO 02/00007, dated Jan. 3, 2002, which is hereby incorporated by reference.  
         [0014]    A single cylinder internal combustion engine  12  is provided on frame  6  for powering both cutting unit  10  and traction drum  8 . A handle assembly  14  extends upwardly and rearwardly from frame  6  to allow an operator to grip and hold handle assembly  14  to thereby guide frame  6  during operation of reel mower  2 .  
         [0015]    This invention relates to a mass damper  20  that is attached to frame  6  of walk greensmower  4 . Mass damper  20  is in the form of an elongated bar, but the shape of mass damper  20  can vary and is not important to this invention. Each end of mass damper  20  has a recess or cavity  22  provided therein, one cavity  22  at one end of mass damper  20  being shown in FIGS. 3 and 4. Each cavity  22  includes a threaded circular bore  24  extending into the interior of mass damper  20 .  
         [0016]    Each end of mass damper  20  is coupled to frame  6  of walk greensmower  4  by a cylindrical elastomeric coupler  26 , such as a coupler made of rubber. Opposite faces of coupler  26  are provided with stub shafts  28  that extend outwardly from the opposite faces of coupler  26 . Thus, one stub shaft  28  extends to the left of coupler  26  and the other stub shaft  28  extends to the right of coupler  26  as shown in FIG. 4. The ends of stub shafts  28  are threaded.  
         [0017]    One coupler  26  is attached to each end of mass damper  20  by taking coupler  26  and placing coupler  26  into the cavity  22  on one end of mass damper  20  and by rotating coupler  26  to thread stub shaft  28  on one face of coupler  26  into threaded bore  24  in cavity  22 . Cavity  22  is sized to substantially enclose coupler  26  after installation. Thus, when both couplers  26  have been installed, couplers  26  will be substantially enclosed in cavities  22  on each end of mass damper  20  with the exception that the other stub shaft  28  on each coupler, i.e. the stub shaft  28  on the opposite face of coupler  26 , will stick out from each side of mass damper  20  much like the handles on a rolling pin.  
         [0018]    Two mounting brackets  30  are provided on frame  6  of walk greensmower  4 . Mounting brackets  30  are spaced apart by a distance that is sufficient to allow mass damper  20  to be placed between them. Each mounting bracket  30  includes an upwardly extending slot  32 . Each outwardly protruding stub shaft  28  on each end of mass damper  20 , namely each stub shaft  28  that sticks out from each end of mass damper  20  after couplers  26  are installed in cavities  22  on each end of mass damper  20 , is simply dropped down into slot  32  on bracket  30 . A nut  34  is then threaded onto the threaded end of stub shaft  28  to clamp stub shaft  28  against the side of bracket  30 .  
         [0019]    When so assembled, each coupler  26  has one stub shaft  28  clamped to a bracket  30  on frame  6  and the other stub shaft  28  is screwed into one end of mass damper  20 . The elastomeric material forming coupler  26  is interposed between these two stub shafts and unites stub shafts  28  together but with stub shafts  28  not being directly connected to one another. Motion between the two stub shafts  28  is permitted, but only by twisting or shearing the elastomeric material forming coupler  26  between the two stub shafts  28 .  
         [0020]    Brackets  30  used to attach mass damper  20  to frame  6  of walk greensmower  4  can be formed as extended flange portions of saddles  40  that mount a grass collecting basket (not shown) to frame  6  of walk greensmower  4 . However, brackets  30  need not be formed as part of something else, but could simply be separate brackets  30  attached to some portion of frame  6  of walk greensmower  4 , i.e. to the cross tube  42  shown in FIG. 3. Thus, brackets  30  could be entirely separate from the grass basket saddles  40  if so desired.  
         [0021]    During operation of reel mower  2 , operation of engine  12  will induce a rhythmic vibration in frame  6  of walk greensmower  4  which is or greatest amplitude in a particular frequency range. In the case of walk greensmower  4  shown herein, the frequency range of concern is 14-20 hz. This vibration is transmitted to mass damper  20  through couplers  26  by a shearing action in couplers  26 , i.e. by twisting couplers  26  between their stub shafts  28  as described above rather than by compression of couplers  26 . This force transmission to mass damper  20  will induce a counter movement in mass damper  20  that is sufficient to substantially damp engine vibration in the frequency range of concern, i.e. in the 14-20 hz range for walk greensmower  4  shown in FIG. 1.  
         [0022]    This results in much less vibration being transmitted to reel cutting unit  10 . Thus, reel cutting unit  10  can cut more precisely and consistently even at low heights of cut since cutting unit  10  is not being vibrated or jiggled as much as it would have been without mass damper  20 .  
         [0023]    The weight of mass damper  20  has to be selected in conjunction with the stiffness of couplers  26  to damp vibration in the desired frequency range according to the following formula:  
       F   =       K   M                             
 
         [0024]    where F=Frequency, K=Spring Constant of the Elastomeric Coupler, and M=Mass of the Mass Damper. For a walk greensmower  4  of the type shown herein powered by a 3.5 hp single cylinder internal combustion engine  12 , a mass damper weighing 11 pounds coupled to frame  6  by rubber couplers sold by Barry Controls of Brighton, Mass., Model A32151 isolators, will effectively damp engine vibrations in the 14 to 20 hz range.  
         [0025]    Various modifications of this invention will be apparent to those skilled in the art. For example, while engine  12  is one vibrational excitation source shown herein, this invention would be useful for damping vibrations arising from some other vibrational excitation source. Considering a triplex reel mower, such a reel mower has a plurality of reel cutting units each carried on the end of a lift arm that joins the reel cutting unit to a riding vehicle. In such a reel mower, the reel cutting units sometimes exhibit a rhythmic bouncing that is undesirable. A properly sized mass damper placed on the end of each lift arm supporting each reel cutting unit, or at such other location as may be appropriate, should help reduce such bouncing by damping the vibrations caused by the vibrational excitation source, which in this case would obviously not be an internal combustion engine.  
         [0026]    In addition, while movement of mass damper  20  is permitted by a shearing action of couplers  26 , this invention is not limited to the use of a shearing action in couplers  26 . Mass damper  20  could be coupled to frame  6  by at least one elastomeric coupler  26  that is deflected by compressing coupler  26  or through a combination of compression and shearing.  
         [0027]    Accordingly, the invention is to be limited only by the appended claims.