Abstract:
A belt tensioning system configured to more effectively maintain the proper tension in a belt that can be engaged and disengaged. Proper tension in the belt is maintained even if the belt stretches or contracts by including a spring biased member between a tension wheel and a pivot frame. The spring member is preloaded such that when the belt stretches the tension wheel is biased against the belt by the force of the spring. Also, by selectively engaging the tension system one can avoid overloading the engine without the need to incorporate a clutch.

Description:
[0001]    This application is being filed on 1 May 2008, as a PCT International patent application in the name of Vermeer Manufacturing Company, a U.S. national corporation, applicant for the designation of all countries except the US, and John T. Bouwers and Justin J. Humpal, citizens of the U.S., applicants for the designation of the US only, and claims priority to U.S. Provisional Patent Application Ser. No. 60/928,861, filed May 10, 2007, which is herein incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to a belt tensioning apparatus. 
       BACKGROUND OF THE INVENTION 
       [0003]    Belt tension systems are found in many different types of machinery including, for example, chippers and grinders. Chippers are used to reduce branches, trees, brush, and other bulk wood products into small chips. A chipper typically includes a feed system for controlling the feed rate of wood products into the chipper, a chipping mechanism, a drive system for powering the feed system and the chipping mechanism, and a discharge chute. 
         [0004]    The chipping mechanism is commonly a large drum that includes blades thereon which is driven by a belt. The belt rotates the drum, enabling the drum to grind, flail, cut, or otherwise reduce the material fed into the chipper into small chips. The proper tension in the belt between the motor and the drum can be difficult to maintain as the belts tend to stretch and contract over time or even during use. Accordingly, there is a need in the art for an improved belt tension system. 
         [0005]    Accelerating chipper drums and other cutting tools from a stopped position to maximum speed can be a challenge because the drums and other cutting/grinding tools are relatively large and heavy. If the belt is fully engaged between the output shaft and the drum during start up, the engine can be overloaded. To avoid overloading the engine in the start up process, typically a clutch is used to interface between the engine and the wheel that drives the belt. The clutch typically mounts adjacent the output shaft of the engine which is typically perpendicular to the length of the chipper or grinder frame. Accordingly, the inclusion of the clutch constrains how narrow the machine can be constructed. Also, since the clutch mechanism is lighter than the engine, the inclusion of the clutch typically undesirably shifts the center of gravity of the machine off to one side of the frame. A belt tension arrangement that could eliminate the need for a clutch is desirable. 
       SUMMARY OF THE INVENTION 
       [0006]    The present disclosure relates to a belt tensioning system that is configured to more effectively maintain the proper tension in the belt that is driven by the motor to drive a cutting/grinding tool. The system of the present disclosure is configured so that the tension in the belt can be maintained even if the belt stretches or contracts. The present disclosure also relates to a belt tension system and method of starting the drum rotating that eliminates the need for a clutch. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of a chipper according to the principles of the present invention with portions of the engine and drum housing removed; 
           [0008]      FIG. 2  is a side view of the drum, engine, and belt tension system of  FIG. 1 . 
           [0009]      FIG. 3   a  is a cross-sectional view of a portion of torsion bar in an unloaded position; 
           [0010]      FIG. 3   b  is a cross-sectional view of a portion of torsion bar in a loaded position; 
           [0011]      FIG. 4  is a side view of an alternative embodiment of the belt tension system of  FIG. 1 ; and 
           [0012]      FIG. 5  is a top view of the embodiment of the belt tension system of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    Referring to  FIG. 1  the tensioning assembly  40  is shown on a chipper. In the depicted embodiment the chipper  10  is mounted to a frame  12  (chassis) that rests on wheels  14 , which enable the chipper  10  to be conveniently moved. The depicted chipper  10  includes a feed chute  16 , which is also commonly referred to as a feed table. The feed chute  16  can be any structure located at the rear of the chipper  10  that facilitates the loading of materials to be chipped into the chipper  10 . (The material to be chipped can be any material that the user desires to reduce to chips. The material is most commonly brush and tree parts, therefore, for convenience the material to be chipped will be referred to herein interchangeably as wood, trees, or brush.) In the depicted embodiment the feed chute includes a flat table portion  24  and two side walls  26 ,  28 . It should be appreciated that many other configurations of the feed chute  16  are possible. Feed chutes are described in greater detail in a related application filed on May 10, 2007 titled WOOD CHIPPER INFEED CHUTE, which is incorporated herein by reference (No. 60/928,937). 
         [0014]    The chipper  10  in the depicted embodiment includes an feed system  18  that grabs and pulls brush from the feed chute  16  into the body portion  20  of the chipper  10  which houses cutters  80  (see  FIG. 2 ) that cut the brush into small chips. The cutter  80  shown has blades  82  mounted on a drum  81 . However, it should be appreciated that the cutter can be any structure that is capable of breaking the material to be chipped into chips. Once the material is broken into small chips, the chips are then projected out of the chipper  10  through a discharge chute  22 . Feed rollers are described in greater detail in a related application filed on May 10, 2007 titled SYSTEM FOR CONTROLLING THE POSITION OF A FEED ROLLER, which is incorporated herein by reference (No. 60/928,926). The cutter drums are described in greater detail in a related application filed on May 10, 2007 titled CHIPPER DRUM WITH INTEGRAL BLOWER which is incorporated herein by reference (No. 60/928,928). In the depicted embodiment the longitudinal axis  11  of the chipper  10  is parallel to the general direction that material to be chipped flows through the chipper  10 . 
         [0015]    Referring to  FIG. 2 , a belt tension assembly  40  is shown. In the depicted embodiment the belt tension assembly  40  includes a belt  42  that extends around a first wheel  87  that is fixed to an end of the drum  81  such that by rotating the wheel  87  the drum  81  rotates. The belt  42  also extends around second wheel  83  attached to the output shaft  84  of the engine  85 . A tensioning wheel  90  presses against the inside of the belt to apply tension to the belt  42  to enable it to frictionally engage the first wheel  87  and the second wheel  83 . 
         [0016]    The tension wheel  90  is mounted to an arm  92 . The arm  92  is connected to a frame  94  that pivots relative to engine  85 . The frame  94  pivots when the cylinder  96  is extended and retracted. To apply tension to the belt  42  the cylinder  96  is extended. To release the tension in the belt  42 , the cylinder  96  is retracted. In the depicted embodiment, the arm  92  is connected to the frame by a torsion spring member  98 . The torsion spring member  98  biases the tension wheel  90  outwardly (upwardly towards the belt) which applies tension to the belt  42 . In use the cylinder  96  is extended to engage the belt  42  and preload the torsion spring member  98 . In the depicted embodiment, the preloading occurs when the frame  94  is pivoted clockwise and the arm  92  is pivoted counterclockwise as a result of the extension of the cylinder  96 . If the belt  42  stretches during operation, the cylinder  96  need not be extended further to compensate because the torsion spring member  98  will bias the tension wheel  90  against the belt  42 . The torsion spring member  98  keeps a relatively constant tension force on the belt  42  to dampen the motion of the belt  42 . 
         [0017]    Referring to  FIGS. 3   a  and  3   b , the torsion spring member (torsion bar)  98  in the depicted embodiment operates according to the rubber torsion spring principle. Four rubber inserts  100  are located in the corners of a square tube  102  and a smaller square tube  104  is located therein. From the neutral position shown in  FIG. 3   a  the square tube  104  is designed to rotate in either the clockwise or counterclockwise direction as shown in  FIG. 3   b . When the square tube  104  rotates, the rubber inserts  100  deform. In the depicted embodiment the larger square tube  102  is mounted to the frame  94  which pivots, and the smaller square tube is mounted to the arm  92 . 
         [0018]    The above arrangement provides a way for applying tension to a belt  42  while the belt  42  stretches or contracts, without having to adjust the extension of the cylinder  96 . The belt tension system  40  above also enables the belt  42  to be smoothly and continuously engaged and disengaged. In the depicted embodiment, there is no clutch positioned between the output shaft  84  and the wheel  83  that drives the belt  42 . To bring the drum  81  up to operating speed from a stopped position, the cylinder  90  can be selectively extended and retracted to cause the belt  42  to grab and release for short periods of time. This pulsing engagement of the belt  42  can be use to gradually increase the rotational speed of the cutter  80  to avoid overloading the engine  85 . 
         [0019]    Referring to  FIGS. 4 and 5  an alternative embodiment of the belt tension system is shown. Similar to the first embodiment, the belt tension assembly  40 ′ of the second embodiment includes a belt  42 ′ that extends around a first wheel  87 ′ that is fixed to an end of the drum (e.g., the drum  81  of the first embodiment) such that by rotating the wheel  87 ′ the drum rotates. The belt  42 ′ also extends around second wheel  83 ′ attached to the output shaft  84 ′ of the engine  85 . In the second embodiment the tensioning wheel  90 ′ presses against the outside rather than the inside of the belt  42 ′ to apply tension to the belt  42 ′. Also, instead of using a cylinder  96  to apply the pressure a lever  110  is used to manually apply the tension to the belt  42 ′. 
         [0020]    In the depicted embodiment, the tension wheel  90 ′ is mounted to an arm  92 ′. The arm  92 ′ is pivotally connected to a frame  94 ′ at pivot  114 . To apply tension to the belt  42 ′ the lever  110  is raised. To release the tension in the belt  42 ′, the lever  110  is lowered. A coil spring  112  is used instead of the torsion spring member  98  of the first embodiment to maintain tension in the belt  42 ′ as the belt stretches. Though in the depicted embodiment the lever  110  is generally straight and arranged horizontally, it should be appreciated that it can be arranged in other orientations as well and can be of other geometric configurations. For example, the lever  110  could be L-shaped and/or arranged vertically. In the depicted embodiment the lever  110  is generally parallel the side of the frame  94 ′ and perpendicular to the output shaft  84 ′. In some embodiment the lever  110  is positioned at an angle relative to the side of the frame  94 ′. The lever  110  could be, for example, within +/−30 degrees from being parallel to the frame  94 ′ (i.e., 30 degrees from being perpendicular to the output shaft  84 ′). It should be appreciated that features from the first embodiment can be combined with features from the second embodiment. For example, the spring  112  could be used with the cylinder  96  instead of with the lever  110 . 
         [0021]    Referring to  FIG. 5 , the distance L 1  from the inside edge of the second wheel  83  to the flywheel mounting plate  116  is relatively small. For example, the distance L 1  on a prior art type machine that includes a clutch and an engine horsepower of 185 is typically about 16 inches. Utilizing the principles described above, the distance L 1  for a chipper with an engine horsepower rating anywhere between 185 HP and 330 HP can be decreased to eight inches or less. In the depicted embodiment, the chipper includes a 215 HP engine and the distance L 1  is only about six inches. Both embodiments depicted show a bearing supported stub shaft as the drive coupler to the engine, however, it should be appreciated that many other configurations are also possible. For example, an engine drive direct coupled shaft that has both an inboard and an outboard bearing could also be used. 
         [0022]    The above arrangement provides a way for applying tension to a belt  42 ′ while the belt  42 ′ stretches or contracts without having to readjust the position of the lever  110 . The belt tension system  40 ′ above also enables the belt  42 ′ to be smoothly and continuously engaged and disengaged. In the depicted embodiment, there is no clutch positioned between the output shaft  84 ′ and the wheel  83 ′ that drives the belt  42 ′. To bring the drum up to operating speed from a stopped position, the lever  110  can be selectively raised and lowered to cause the belt  42 ′ to grab and release for short periods of time. This pulsing engagement of the belt  42 ′ can be use to gradually increase the rotational speed of the cutter to avoid overloading the engine. Alternatively, the lever  110  can be gradually raised causing the belt  42 ′ to transition from slipping to gripping over a longer period of time to allow the drum to gradually increase its speed. 
         [0023]    In both depicted embodiments the engine can be mounted along the longitudinal axis of the chipper  10  so that the weight on the wheels of the chipper on the left and right sides is balanced. In the depicted embodiments the weight on the wheels on either side is within (70-30) percent and more preferably within (60-40) percent. The absence of a clutch, which is typically mounted near the output shaft of the engine, enables the weight of the engine to be distributed closer to the center of the chipper. 
         [0024]    It should be appreciated that the belt tension systems of the invention can be used in other types of machinery as well. The use of the belt tension system in a chipper is only one potential environment for the system. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.