Abstract:
A stump grinder having a clutch assembly which includes a system for cooling the clutch bearings. The clutch assembly is mounted onto a crankshaft extending from the power source for the grinder and a fan is keyed to the crankshaft. The fan that is adapted to drive air over the clutch assembly during operation and thereby cool the same. More specifically, the fan drives air toward the clutch bearings to reduce the temperature thereof.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     This invention generally relates to stump grinders. More particularly, the invention relates to a clutch assembly for a stump grinder. Specifically, the invention relates to a clutch assembly for a stump grinder which includes a means for cooling the bearings.  
         [0003]     2. Background Information  
         [0004]     Land frequently has to be cleared of trees in order to allow for fields to be planted, buildings to be built or for the construction of roads. Cutting the trees down is relatively easy compared to the removal of the stumps which remain after the trees have been felled. Stumps can be pulled out of the ground by tractors or other heavy machinery or can be ground into small wood chips by a stump grinder.  
         [0005]     Many larger commercial stump grinders are available for use by building contractors and others who frequently need to remove large numbers of tree stumps. The operators of this type of equipment are experienced and know both how to use the machinery and how to correctly and efficiently remove tree stumps without damaging the machinery.  
         [0006]     However, there is a growing market for smaller stump grinders that can be rented by individuals to remove the occasional tree stump. The renters of such devices are typically inexperienced in both stump removal and in the operation of heavy machinery. Consequently, in order to provide a stump grinder for such rental use, the manufacturers of these devices have incorporated many features typically found in machinery that the renter may be familiar with, such as lawnmowers. This is done to make it easier for this occasional user to operate the equipment. However, the inexperience of these users in removing stumps and in operating heavy equipment tends to result in incorrect operation of the equipment, overheating of the machines and consequent damage to various components in the stump grinders. The stump grinders therefore have to be frequently repaired and are consequently out of action for significant periods of time. This results in increased costs for operating the machines and loss of rental income to the rental company. Furthermore, the downtime for the grinders also results in the rental company having to carry more machines than would be necessary if the equipment did not need constant repair.  
         [0007]     The smaller rental type stump grinders have clutch assemblies that are similar to those found in lawnmowers. The clutch assemblies in these grinders tend to have a high failure rate because of the heavy duty use of the machines and inexperience of the operators of such devices.  
         [0008]     There is therefore a need in the art for a stump grinder that is less easy for an occasional operator to damage and therefore does not require frequent repair.  
       SUMMARY OF THE INVENTION  
       [0009]     The inventor of the instant device has recognized that one of the significant factors contributing to the high failure rate of rental-type stump grinders is the overheating of the clutch assembly during operation of the machine. The device of the present invention is a stump grinder that includes a clutch assembly which incorporates a cooling system for cooling the clutch assembly during operation. Specifically, the stump grinder of the present invention includes a fan that is adapted to drive air over the clutch assembly during operation and thereby cool the same. The fan has been shown to reduce the temperature of the clutch bearings by as much as 30%, thereby extending the life of the clutch assembly. The stump grinder of the present invention therefore tends to require less maintenance and downtime for repair and therefore tends to increase the rental income for companies which rent out these machines to occasional users. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The preferred embodiments of the invention, illustrative of the best mode in which applicant has contemplated applying the principles, are set forth in the following description and are shown in the drawings and are particularly and distinctly pointed out and set forth in the appended claims.  
         [0011]      FIG. 1  is a side elevational view of a stump grinder in accordance with the present invention;  
         [0012]      FIG. 2  is a partial side elevational view of the stump grinder of  FIG. 1  with a panel removed to show the details of the clutch assembly in accordance with the present invention;  
         [0013]      FIG. 3  is a partially exploded perspective view of the engine and clutch assembly; and  
         [0014]      FIG. 4  is a cross-sectional front view of the clutch assembly. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     Referring to  FIGS. 1 &amp; 2 , there is shown a stump grinder in accordance with the present invention and generally indicated at  10 . Grinder  10  comprises a body portion  12  and a grinding portion  14 . A plurality of wheels  16  are provided on body portion  12  and grinding portion  14  to enable grinder  10  to travel over a surface  18 . Grinding portion  14  is mounted to body portion  12  in such a manner that grinding portion  14  can be vertically raised and lowered and can be moved horizontally from side to side. This movement is made possible by the provision of one or more hydraulic cylinders  20 . The controls  22  for stump grinder  10  preferably are mounted on body portion  12 . As will be understood by those skilled in the art, stump grinder  10  may include an engine (not shown) for moving body  12  over surface  18  or may include a handle (not shown) for an operator to manually move grinder  10 . Body portion  12  may further include a seat (not shown) for an operator to sit in to drive the machine over surface  18 .  
         [0016]     Grinding portion  14  of stump grinder  10  includes a grinding wheel  24  mounted at the front end thereof. Grinding wheel  24  includes a plurality of cutting surfaces  26  for cutting into a tree stump when wheel  24  is moved into contact therewith. Grinding wheel  24  preferably is powered by a dedicated power source  28  such as a conventional combustion engine which is mounted on grinding portion  14 . Grinding wheel  24  is operationally connected to power source  28  via the electric clutch assembly  30  in any manner known to those of ordinary skill in the art. Grinding wheel  24  is rotated, causing cutting surfaces  26  to bite into the tree stump (not shown) and grind the same away. The hydraulic cylinders  20  enable the operator to raise and lower grinding portion  14  and/or grinding wheel  24  and to move the same from side to side. This allows the operator to position wheel  24  correctly and to maneuver the same to engage the tree stump and cut small pieces away therefrom until the stump is totally ground away. Grinding portion  14  preferably includes a grinding wheel cover  32  and a deflection plate  34  to shield the operator from flying debris as the stump is ground down. Deflection plate  34  covers the linkage  36  ( FIG. 2 ) between clutch assembly  30  and grinding wheel  24 , thus protecting these components from flying wood chips as well.  
         [0017]      FIG. 3  shows a power source  28 , which is a standard combustion engine; clutch assembly  30  and the clutch assembly cooling system  38  of stump grinder  10 . Referring additionally to  FIG. 4 , crankshaft  40  extends outwardly from engine  28  and a tubular rotor  42  is fitted over crankshaft  40  so that crankshaft  40  lies within the bore  44  of rotor  42 . A key  46  secures rotor  42  and crankshaft  40  together so that they rotate in unison whenever crankshaft  40  is driven by engine  28 . Crankshaft  40  further includes an axial slot  48  that terminates at an end  40   a  of crankshaft  40 .  
         [0018]     Clutch assembly  30  includes clutch plates  50  which have a front end  50   a  and a nose portion  50   b . Clutch plates  50  further include an axial central bore  52  therethrough. Crankshaft  40  and rotor  42  are received through bore  52  and are separated therefrom by clutch bearings  54 . Bearings  54  allow rotor  42  and crankshaft  40  to rotate freely within bore  52 . Clutch assembly  30  is engaged and disengaged in a manner which will be well known to those of ordinary skill in the art.  
         [0019]     In accordance with a specific feature of the present invention, clutch assembly  30  is provided with a cooling system  38 . As is shown in  FIG. 4 , cooling system  38  comprises a fan  56  which is secured to and rotates with crankshaft  40 . Fan  56  has a disc-shaped body  58  having a plurality of fins  60  radiating outwardly away from a central aperture  62 . Fins  60  further each include a flange  64  extending outwardly away from a rear surface  58   a  of body  58  and substantially at right angles thereto. It will be understood that fan  56  may be of any other desirable configuration without departing from the spirit of the present invention.  
         [0020]     A threaded bolt  66  is inserted through a first washer  68 , through aperture  62  in fan  56 , through a second washer  70  and into threaded slot  48  of crankshaft  40 . Fan  56  has an outer diameter A-A′ ( FIG. 4 ) which is smaller than the outermost diameter B-B′ of clutch plate  50 , but larger than the outermost diameter C-C′ of the nose portion  50   b  of clutch plates  50 . Furthermore, washer  70  has a diameter D-D′ which is greater than the outer diameter E-E′ of rotor  42 . Washer  70  does not therefore extend upwardly over the entire side surface of bearings  54 . Washer  70  covers approximately one third of the side surface of bearings  54  as shown in  FIG. 4 . Fan  56  is positioned so that flanges  64  extend toward front end  50   a  of clutch plates  50  and any air moved by fan  56  is driven toward front face  50   a  of clutch plates  50  as is shown by  FIG. 4 . Fan  56  is separated from end  42   a  of rotor  42  by washer  70 , whereby a space X-X′ separates fan  56  and outermost surface  72  of bearings  54 . As may be seen from  FIG. 4 , bearings  54  are preferably recessed in nose portion  50   b  of clutch plate  50 , such that the outermost surface  72  of the bearings  54  lies inwardly of outer surface  74  of nose portion  50   b.    
         [0021]     Clutch assembly  30  is covered with and protected by a plate  76  ( FIG. 1 ) which includes a plurality of air holes  78  therein. Plate  76  may be formed as a portion of deflection plate  34  or may be a completely separate entity which interlocks with deflection plate  34 . Plate  76  is disposed so that air holes  78  lie adjacent fan  56  when plate  76  is in position over clutch assembly  30 .  
         [0022]     In operation, power source  28  is engaged causing a rotation “Y” in crankshaft  40  ( FIG. 4 ). Crankshaft  40  is keyed to rotor  42  and consequently rotor  42  also rotates in the direction of arrow “Y”. Fan  56  is fixedly secured by bolt  66  to crankshaft  40  and consequently fan  56  also rotates in unison with crankshaft  40  and rotor  42 . As fan  56  rotates, air is sucked through holes  78  in plate  76  ( FIG. 1 ) and is driven toward the front face  50   a  of clutch plates  50 . Because washer  70  has a reduced diameter relative to that of the bore  52  of clutch plates  50 , air drawn through air holes  78  is forced inwardly toward bearings  54  (shown by the arrows in  FIG. 4 ). This forced air cools bearings  54  and the surrounding parts of the clutch plate  50  that it contacts. It has been found that including a fan  56  in clutch assembly  30  causes a reduction of around 30% in the temperature of bearings  54 . This reduces the tendency of the bearings  54  to overheat and fail and the fan  56  thereby extends the life of the clutch assembly  30  and reduces the need for maintenance, repair and replacement of the same. It should be noted that because fan  56  is secured directly to crankshaft  40 , fan  56  is driven by the engine  28  whether the clutch is engaged or disengaged.  
         [0023]     In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed.  
         [0024]     Moreover, the description and illustration of the invention is an example and the invention is not limited to the exact details shown or described.