Patent Publication Number: US-2006012238-A1

Title: Power take off

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This is a continuation of Ser. No. 10/100,502, filed Mar. 18, 2002, now U.S. Pat. No. 6,945,608, incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTIONS  
      1. Field of the Invention  
      This relates to power take off assemblies, and saws using power take off assemblies, for example concrete and slab saws and self propelled saws.  
      2. Related Art  
      Power saws typically include a motor, engine or other system for producing drive power, a saw blade or other cutting device and a support frame structure for supporting the engine and cutting blade. The power system may be an internal combustion engine, a hydraulic motor, an electric motor or the like. The power system can drive the cutting blade through a mechanical or hydraulic drive system, but a belt drive system is common. The size and dimensions of the saw will vary according to usage and application.  
      For large projects, higher horsepower levels are desired for the saw. Higher horsepower allows the use of larger cutting blades, reduces cutting time and may provide higher cutting speeds. However, higher horsepower levels usually mean larger engines and often larger saw dimensions. Larger saws may also mean less maneuver ability.  
      In some applications, structures may be such that access to an area for cutting may be limited. For example, in high-rise buildings, concrete floors and/or walls may be poured or installed on an ongoing basis, and detail work may come later. Access openings such as door ways, floor openings, and the like, as well as concrete openings for fixtures may be formed after concrete slabs and walls are poured and the concrete hardened. Similar work may also be done on other concrete projects after the concrete has hardened. However, the equipment to be used for cutting in those areas may be limited by such restrictions as access opening size, elevator size and the like. For example, door ways in buildings may be 32 inches in width, thereby limiting the width of the saw to less than 32 inches. Therefore, the amount of horsepower for a saw and other operating characteristics such as blade size and the like may be limited for a given application by such factors as access opening size and the like.  
      Increasing the horsepower for a saw often results in a larger saw. The consequences of a larger saw may be most noticeable where the saw engine is oriented sideways relative to the forward direction of motion of the saw. In these saws, the engine crank shaft and the stub shaft attached to it extend sideways from the engine, and one or more drive belts couple the stub shaft sheave to a sheave for driving a saw blade shaft. If the engine is made larger, the width of the engine with the stub shaft typically increases, which may make the saw less maneuverable. Therefore, saw improvements may have undesirable consequences for some users.  
      In saws with a belt drive for the saw blade, the sheave is typically mounted to and held on the stub shaft using a shaft key fitting into a longitudinal groove in the stub shaft and a corresponding groove in an internal surface of the sheave. The stub shaft, key and sheave are subjected to side loading by the belts during normal operation. The side loading and the rotation in turn produces a cyclical fatigue load on the stub shaft, often focused in the area of the shaft key. Such loads sometimes produce fatigue and sometimes fractures in the shaft, leading to drive failure. Increasing the saw horsepower produces more cyclical fatigue loads on the shaft and may increase the likelihood of shaft failure.  
     SUMMARY OF THE INVENTIONS  
      Apparatus and methods are described for providing a saw with a smaller profile. A saw and method of operation are also provided that would allow a higher horsepower engine with the same overall saw dimension as conventional saws, or even smaller. A saw and saw operating method are shown that separate the drive function for the saw output and the support function for the saw output, or reducing the load function of the stub shaft so the primary function of the stub shaft is to turn the output sheave. Additionally, a saw and operating method are further described that reduces cyclical fatigue on the rotating shaft, and that may also reduce load placed on the engine crank shaft. Engine operation and performance can be improved and made more reliable, engine horsepower can be increased without adversely affecting the overall size of the saw, and in some cases, the saw size can be reduced.  
      In one example of an assembly described herein, a power takeoff assembly includes a drive element, in one example a stub shaft, for rotation with a rotating element. A stationary support supports an output element. The output element rotates with the drive element, for example while being supported by the stationary support. With such an arrangement, load on the rotating element can be reduced and applied more to the stationary support, and the loading is preferably fixed and non-movable for example when the output element is positioned on the stationary support. In such a configuration, the load bearing function and the drive function can be separated. In one example, the drive element may be a stub shaft attached to a fly wheel of an engine extending into a bearing supporting shaft mounted to an engine housing, and the output element rotates on the bearings. The output element can be coupled to the stub shaft through a coupling element. The output element is supported by the shaft mounted on engine housing, and is driven about the shaft by the stub shaft through the coupling element.  
      In another example of a power takeoff assembly, a drive element rotates with a rotating element and a stationary support supports an output element that rotates with the drive element. The drive element and the stationary support preferably extend in the same direction, and in one preferred form they are co-axial. For example, the drive element can be a stub shaft and stationary support can be a hollow shaft supported by the engine housing with the stub shaft extending through the hollow shaft. The output element rotates on bearings on the hollow shaft and is driven by the stub shaft through a coupling element.  
      In a further example described herein, a drive assembly and method has a rotating drive and a stationary support. An output element is supported by the stationary support and coupled to the rotatable drive so as to rotate about the stationary support. The output element also includes surfaces for receiving a flexible element to be driven by the output element. The drive assembly separates the drive function for the output element and the support function for the output element so the drive assembly is more reliable. In one example, the rotating drive can be a drive shaft such as a stub shaft and may be mounted to an engine fly wheel through a removable drive plate. The drive shaft can include splines for engaging a coupling element which in turn engages the output element. The stationary support in one example includes a hollow shaft into which the drive shaft extends and engages with the coupling element. The stationary support is preferably mounted to a housing or other stationary support structure so as to reliably support the output element. In the context of an engine, the housing may be the engine block, and the stationary support can be the hollow shaft mounted, fixed or otherwise supported by a fly wheel cover. In another example of a drive assembly and method, the drive assembly may be used for driving a saw blade or other cutting device. The output element may include one or more surfaces for receiving drive belts, which are then run around an input sheave for the saw blade.  
      In an additional example of a method and apparatus described herein, a saw includes an engine with a rotatable output shaft and a support stationary relative to the engine. An output element is supported by the stationary support and rotates with the rotatable output shaft. A cutting blade is driven by the output element, for example through one or more drive belts or the like. In one such example, the stationary support can be a support shaft and the support shaft can be mounted to the engine block, or another portion of a stationary structure can be used to support the support shaft. The output element may be a sheave turning on bearings on the support shaft.  
      In one method of providing a drive assembly, a rotating drive can drive an output element supported by a rotationally fixed support. The output element is then rotated by the rotating drive, which rotation is transferred to a work piece such as through drive belts or the like. The output element thereby rotates on a structure other than the rotating drive, thereby allowing the load on the output element to be supported by the fixed support rather than being applied to the rotating drive. This drive method can be used as a power takeoff, for example on saws, cutting devices and other apparatus.  
      In another example of apparatus, a kit may be provided for assembling a power takeoff assembly onto a structure such as an engine, a saw or other machine. The kit may include an output support for supporting a rotatable output device, for example a sheave, and a coupling element for coupling the output device to a rotatable element, for example a stub shaft. The kit may also include the stub shaft itself, especially where the stub shaft may have engagement surfaces, such as for receiving the coupling element, different from the stub shaft on the original equipment. In one example, the output support is a hollow shaft into which the stub shaft extends. The output support can include a mounting plate, web or other mounting structure for mounting the output support to a non-rotatable structure, for example an engine block. The output support preferably includes bearings between the support and the output device so that the output device can rotate freely about the support once assembled.  
      These and other structures and methods are described further in the following detailed description, with reference to the drawings, a brief description of which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a side elevation and partial cutaway view of a machine with a power takeoff assembly, in the form of a slab saw such as that with which the apparatus described herein can be used.  
       FIG. 2  is a front elevation view and partial schematic of the saw of  FIG. 1 .  
       FIG. 2A  is a detail cutaway of the fly wheel assembly of  FIG. 2 .  
       FIG. 3  is a partial exploded view of one example of a power takeoff assembly that can be incorporated on a saw or retrofit onto an existing saw.  
       FIG. 4  is a transverse section and isometric view of one example of a power takeoff assembly that can be incorporated on a saw or retrofit onto an existing saw.  
       FIG. 5  is a transverse section and partial exploded isometric view of one example of a power takeoff assembly that can be incorporated on a saw or retrofit onto an existing saw.  
       FIG. 6  is an isometric view of a drive assembly for use with the power takeoff assembly of  FIG. 4 .  
       FIG. 7  is a front elevation view of the drive assembly of  FIG. 6 .  
       FIG. 8  is a transverse section of the drive assembly take along line  7 - 7  of  FIG. 7 .  
       FIG. 9  is an isometric view of a coupling element for use with a power take off assembly of  FIG. 4 .  
       FIG. 10  is a front elevation view of an output element in the form of a sheave for use with the power takeoff assembly of  FIG. 4 .  
       FIG. 11  is a transverse section of the output element of  FIG. 10  taken along line  11 - 11 .  
       FIG. 12  is a front elevation view of the coupling element of  FIG. 8 .  
       FIG. 13  is a transverse section of the coupling element taken along line  13 - 13  of  FIG. 12 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The following specification taken in conjunction with the drawings sets forth the preferred embodiments of the present inventions in such a manner that any person skilled in the art can make and use the inventions. The embodiments of the inventions disclosed herein are the best modes contemplated by the inventor for carrying out the inventions in a commercial environment, although it should be understood that various modifications can be accomplished within the parameters of the present inventions.  
      Mechanical drives and power takeoff assemblies find applications in a number of areas. For the present descriptions, examples of power takeoff assemblies will be given in the context of flat saws or concrete slab saws such as those used to cut pavement, concrete in buildings and other structures, and the like. However, it should be understood that the inventions are not limited to the examples, and can be extended and are applicable to other methods and apparatus as well.  
      Concrete saws with which the present inventions can be used include flat or slab saws such as  20  shown in  FIGS. 1 and 2 . The saw includes an engine  22  mounted to and extending along the width-wise axis of a saw frame  24 . The engine  22  is reliably mounted to and supported by the frame  24  through an engine mount  25  or other mounting means. The drive end of the engine crank shaft is coupled to a drive plate assembly  26  so that the rotational motion of the crank shaft can be transferred to the drive plate assembly  26 . In the example of the saw shown in  FIGS. 1 and 2 , the engine is mounted transversely of the frame allowing a substantially direct drive between the engine crank shaft and a pulley used for driving the saw blade. For transversely mounted engines, changes in engine design may affect how the saw is used. In an example where the engine size is increased for greater horsepower, the length of the engine and therefore the width  27  ( FIG. 2 ) of the saw may increase significantly, even to the point where the saw may no longer fit through a standard 32 in. wide doorway. Therefore, practical limitations may otherwise preclude desirable improvements to saws. However, improved designs such as those described here may nonetheless allow improvements to the engine without significantly affecting how and where the saw can be used. Additionally, retrofit of existing saws using apparatus described herein may allow those saws to have a narrower width than presently exists.  
      A transmission  28  is mounted at a rear portion of the frame  24  for engaging and driving wheels  30  through a chain or other drive link  32 . A blade depth control mechanism  34  is mounted on the lower side of the frame  24  to control the depth of cut by the saw blade  36 . Rollers  38  support and help to control the depth of cut of the blade as they rest on the work surface. The work surface may be concrete or other pavement or floor, or any other work surface. A control handle  40  and control handle linkage  42  control a Hydro-static pump, the transmission  28  and the depth control assembly  34 .  
      In some conventional saws, as with many other types of motor-driven the equipment, the motor crank shaft  44  ( FIG. 2 ) extends from the engine  22  and turns a fly wheel  46 . In the embodiment of the saw shown in  FIG. 2 , the fly wheel is enclosed within a bell housing or cover plate  48  mounted to the engine block through fasteners  50 , two of which are shown in phantom in  FIG. 2 . A conventional stub shaft  52  is mounted to the fly wheel  46  through a drive plate  54  using appropriate fasteners, as is known to those skilled in the art. The stub shaft  52  extends through the cover plate  48  through bearings (not shown). A sheave  54  is mounted to and supported by the stub shaft  52  and is fixed to the stub shaft by a key and set screw or other fastener, as is also known to those skilled in the art. The sheave  54  may include a number of grooves or other surfaces for receiving one or more belts  56  for driving a blade pulley  58  mounted to a blade shaft  60 . The blade shaft  60  is mounted and supported relative to the frame in a conventional manner.  
      Considering the fly wheel in more detail, the fly wheel  46  is mounted to crank shaft  44  within the housing defined by the engine block  22 . The fly wheel is mounted to the engine crank shaft  44  by conventional means. The side of the fly wheel opposite crank shaft includes a number of pockets, recesses or seats into which parts of a power takeoff assembly are mounted. Specifically, an inner seat  62  receives a power takeoff drive disk  64  held in place by one or more fasteners. A drive shaft is then mounted and fixed to the drive disk  64  through one or more fasteners. Other means may also be provided for mounting and supporting a drive shaft relative to the crank shaft  44 .  
      In operation, the engine may be started with the blade raised so that the crank shaft  44  then turns the fly wheel to rotate the sheave  54 . The sheave  54  drives belts  56  which in turn rotates the blade shaft  60  turning blade  36 . The blade is brought down into contact with the work surface and a groove cut into the work surface. In one example of one aspect of the present inventions, a power takeoff assembly  66  ( FIG. 4 ) can be used on an engine such as a saw or other equipment on which such assemblies are used, for example to form part of a drive assembly such as for driving a saw blade. For present purposes, the power takeoff assembly in the present example will be described for use on a slab saw or flat saw such as that described with respect to  FIGS. 1 and 2 , but it is understood that the assembly can be used on structures other than saws. Additionally, fewer than all of the features of the power takeoff assembly  66  described herein as an example may be used on the equipment while still achieving at least one of the benefits of the assembly, even though one or more features are omitted. Fewer than all of the components can still be used to achieve some of the benefits of the inventions.  
      The power takeoff assembly  66  preferably includes a drive element  68 , a stationary support  70  and an output element  72 . In one preferred form, the drive element  68  moves with the motion of the engine, which in the present case is rotational motion, while support  70  is stationary relative to the engine by being mounted to the engine. Alternatively, the support for the output element  72  can also be moving, but possibly slower than the drive element  68 . One benefit of having the support for the output element  72  separate from the drive element  68  is that the output element would not be applying the same load and forces to the drive element  68  compared to the loads and forces experienced by conventional stub shafts. However, a preferred configuration is to have the support  70  stationary relative to the engine while allowing the drive element to move freely with the drive of the engine.  
      The power takeoff assembly also preferably includes a coupler or coupling element coupled between the drive element  68  and the output element  72 . The coupling element  74  can take a number of forms, and preferably transfers the drive motion from the drive element  68  to the output element  72 .  
      Considering the drive element  68  in more detail ( FIGS. 3-8 ), the drive element  68  includes a mounting element  76 . The mounting element  76  mounts the drive element  68  to the engine or other power source. The mounting element  76  in the form described herein is a plate  78  having a configuration similar to a conventional power takeoff drive plate and includes one or more openings  80  for receiving fasteners to mount the drive plate onto the fly wheel of a saw engine. The mounting element  76  can take any number of forms, but is generally configured to complement the drive structure to which it is mounted.  
      The drive element  68  also preferably includes a drive shaft  82 . The drive shaft  82  transmits the drive motion of the engine to the output element  72 . In the present example, the drive shaft  82  is preferably splined to more reliably transmit the drive motion of the engine to the coupler  74 . The drive shaft  82  is mounted to the drive plate  78  through a spline drive  84 . The spline drive  84  includes complementary internal splined surfaces for receiving the splined drive shaft  82 , and the two components are preferably welded to each other on each side of the drive plate  78  about the circumference  86  and  88 , respectively, of the drive shaft  82 . The spline drive  84  fits into a similar-sized opening in the drive plate  78  and is preferably welded on each side of the drive plate around the circumference  90  and  92 , respectively, of the spline drive  84 .  
      The drive shaft  82  includes an end portion  94  opposite the spline drive  84 . The end portion  94  is also splined and forms an engagement surface  96 . The engagement surface  96  is used in this example to engage the coupler for transferring the rotating engine motion to the output element  72 . The longitudinal or axial extent of the engagement surface is preferably sufficient to reliably engage the coupler  74 . The drive shaft  82  also preferably includes a mounting surface such as a threaded opening  98  for receiving a mounting bolt or other fastener ( FIG. 4 ) for mounting the coupler  74  on the drive shaft.  
      When the drive assembly  68  is mounted to the engine, it will rotate about a central axis  100  ( FIG. 3 ) with rotation of the engine crank shaft. It transfers the engine rotational motion to the coupler  74 . As described more fully below, the only significant loading on the drive element  68  results from the counter rotational or resisting force produced by the saw blade as returned through the coupler  74 .  
      The output support  70  ( FIGS. 3 and 4 ) is configured to be stationary relative to the engine or other motion-generating device. The output support in the example shown in  FIGS. 3 and 4  is mounted and secured to the bell housing of the engine so as to be stationary relative to the engine. The output support can also be supported by another structure other than that which produces the movement in the drive shaft, including the support frame or structures which are themselves supported by the support frame. Additionally, the output support can also function, though not as well, even if it were rotating on its own and separate from the rotating drive shaft, because the side loading or cyclical loading on the drive shaft would be reduced or still eliminated. However, the preferred configuration is to have the output support stationary relative to the engine producing the rotational movement of the drive shaft.  
      The output support  70  is preferably in the form of a fly wheel cover with an axially-extending support for an output element, for example output element  72 . In the example shown in  FIGS. 3 and 4 , the output support  70  includes a plate or cover in the form of a bell housing  102  having a flange  104  for mounting the bell housing to the engine block. The flange includes a number of openings  106  for receiving fasteners (not shown). The number of openings is preferably sufficient to securely mount the bell housing to the engine block as well as to maintain stationary the axially-extending support for the output element under normal operating conditions.  
      The output support  70  includes a preferably hollow cylinder forming a housing tube  108 . The housing tube is preferably rigidly mounted, fixed or otherwise supported by the bell housing  102 , such as by welding. The housing tube may also include a radially-extending disk  110  to help support the housing tube  108  in the bell housing. The housing tube  108  is preferably a right circular cylinder having a smooth outer surface and smooth inner surface with a counter bore. The outer surface receives and supports an output element, and the tube also receives and houses the drive shaft  82 , allowing the drive shaft to freely rotate within the housing tube, preferably with sufficient clearance to provide an air gap between the outer surface of the drive shaft and the inside surface of the housing tube  108 . As can be seen in  FIG. 4 , the drive shaft  82  has a length that when properly positioned within the housing tube  108  extends slightly past the open end of the tube  108 . The length of the drive shaft  82  permits access to the drive shaft for the coupler  74 . The open end of the housing tube includes a counter bore having an inside diameter slightly larger than an inside diameter of the remainder of the housing tube, also to accommodate a portion of the coupler  74  while leaving an air gap between the housing tube and the coupler.  
      Mounting arrangements can be used for the housing tube  108  other than a bell housing or plate structure. However, using a structure similar to existing bell housings permits easy retrofit on existing saws and other equipment. Additionally, support surfaces other than a housing tube can be used to support the output element. Surfaces other than a smooth surface on a hollow shaft can be used, but the smooth surface of the housing tube  108  easily supports the output element, as will be apparent from the description set forth below. The support element  70  is preferably configured in the manner shown in  FIGS. 3 and 4  for ease of use, its compact size and its simplicity.  
      The output element  72  in the example shown in  FIGS. 3 and 4  is configured to rotate with the drive shaft about the housing tube  108 . The output element  72  in this example has the form of a sheave  112  having at least one surface  114  for transmitting the rotation of the sheave to a belt, such as belt  56 , extending about the sheave. The sheave is preferably supported by bearings, such as first, second, third and fourth bearings  116 - 122 , respectively, which are in turn supported by the housing tube  108 . The bearings can be part of the sheave as an assembly, as represented in  FIG. 3 , or they can be part of the support formed by the housing tube  108 . The sheave preferably includes five grooves  124   a - e  for receiving respective belts  56  for driving corresponding pulleys  80  on the blade shaft  60  ( FIG. 2 ). A sixth groove  126  may be deeper and larger to accommodate a drive belt for the transmission system on the saw.  
      The sheave  112  includes engagement surfaces for coupling to the drive element, such as through the coupler  74 . In the example shown in  FIGS. 3 and 4 , the engagement surfaces are threaded openings  128  for receiving screws, bolts or other fasteners (not shown) for securely mounting the coupler  74  on the sheave. Other mounting arrangements can be used.  
      The sheave preferably rotate freely about the housing tube  108 , and is properly positioned axially relative to the housing tube  108  through engagement with the coupler  74 , as will be apparent from the description below. Other ways for reliably positioning the sheave axially relative to the support  70  can also be used.  
      The bearings  116 - 122  preferably extend almost the entire axial length of the interior of the sheave and preferably the entire outside length of the housing tube  108 . The bearings provide adequate support for the sheave during normal operation. Adjacent bearings may be separated by shims  130 , as would be known to those skilled in the art. The bearings are preferably sealed bearings or other friction-reducing components.  
      The coupling element or coupler  74  couples the drive shaft  82  to the output element  112 . It takes what is in the present example rotational motion from the engine and transfers it to the output element in the form of the sheave  112 . The coupler  74  can take any number of configurations.  
      Preferably, it securely engages both the drive shaft  82  and the sheave  112  under normal operating conditions. In the example of the coupler  74  shown in  FIGS. 3, 4 ,  12  and  13 , the coupler includes a drive coupler  132  and a spline coupler  134 . The drive coupler  132  is rigidly and securely fixed to the spline coupler  134 , such as by welding or otherwise. The drive coupler and the spline coupler can also be formed integral with each other or as more than two parts joined together.  
      The spline coupler  134  includes complimentary spline surfaces  136  for engaging the spline drive shaft  82 . As shown in  FIG. 4 , the spline surfaces  136  engage the engagement portion  96  on the output shaft  82  over a sufficient length to insure reliable transfer of rotational motion from the spline drive shaft  82  to the coupler  74 . The spline coupler has an outside dimension slightly smaller than the inside diameter of the counter bore in the housing tube  108  so that the drive shaft  82  and the coupler  74  can freely rotate within the housing tube  108 . Additionally, the drive coupler  132 , when the coupler  74  is mounted to the drive shaft  82 , is spaced sufficiently from the end of housing tube  108  to provide an air gap and minimize any possible frictional engagement.  
      The coupler  74  is preferably formed strong enough to withstand the stresses and forces applied to it during normal operation, especially the sheer forces applied through rotation of the drive shaft  82  and the counter forces developed in the sheave  112 . In the example of the coupler  74  shown in  FIGS. 12 and 13 , the coupler is formed from two parts, but other configurations are possible. In that example, the spline coupler  134  is welded to the drive coupler  132  about the circumferential wall  138  of the spline coupler in a recess  140  formed in the back of the drive coupler. A weld is preferably formed about the entire circumference of the spline coupler. The base  142  of the spline coupler is also preferably welded to the drive coupler  132  through one or more openings formed through the front of the drive coupler. In the example shown in  FIG. 12 , two pair of holes  144  are formed in the front of the drive coupler outside of a central opening  146 , where each pair is positioned on a diameter of the drive coupler and perpendicular to a diameter on which the other pair is formed. Each hole is preferably formed with a counter sink surface  148 , and each of the four openings in the example shown in  FIGS. 12 and 13  are filled with weld material. Additional welds may also be used or other attachment methods may be used. Additionally, the opening  146  receives a bolt or other fastener (not shown) for securely mounting the coupler  74  onto the drive shaft  82 .  
      The drive coupler  132  includes a mounting flange  150  having a thickness approximately half the overall thickness of the drive coupler. The mounting flange  150  mounts the coupler  74  onto the sheave  112 . The mounting flange engages the sheave and transmits the rotational motion of the drive shaft  82  to rotational motion of the sheave  112 . In the example shown in  FIGS. 12 and 13 , the mounting flange includes engagement surfaces in the form of fastener openings  152 , each of which is preferably formed with a counter sink surface  154  for receiving the head of an appropriate fastener threaded or otherwise set into the corresponding engagement surfaces in the form of threaded openings  128  in the sheave  112 . Other methods of engaging the coupler with the sheave are also possible. The engagement surfaces in the form of splines  136  on the coupler  74 , and the mounting flange  150  with the fastener openings  152 , together couple the rotating drive shaft  82  to the sheave  112 .  
       FIG. 3  shows various components that can be used to assemble a power takeoff assembly or drive assembly for such things as engines, saws for example slab and other concrete saws, and other devices.  FIG. 4  shows parts assembled into such a power takeoff assembly or drive assembly, and a form of the assembly that may be supplied in kit form. To assemble the components, for example onto a saw, drive assembly  68  is mounted onto the fly wheel  46  through fasteners. The bell housing and support shaft forming the support element  70  are then mounted to the engine block. The housing tube  108  and drive shaft  82  are dimensioned in such a way as to leave an air gap between them when the shaft extends within the tube and leaving sufficient clearance during normal operation to minimize the possibility of contact between the drive shaft and the tube. The bearings  116 - 120  are placed over the housing tube  108 , if they were not previously installed on the tube, and the sheave  112  slipped over the bearings. The coupler can already be mounted to the sheave, or the coupler can be fastened to the sheave after the sheave is placed over the bearings, and the coupler  74  securely mounted to the drive shaft  82  through a fastener. Alternatively, the support element  70 , bearings, sheave and coupler can be pre-assembled and installed after the drive element  68  is mounted. Appropriate belts  56  and a transmission drive belt can then be placed on the sheave and appropriate pulleys for operation.  
      The assembly of the foregoing example may reduce and even entirely eliminate side loading and cyclical loading on the drive shaft, and therefore on the engine crank shaft. Consequently, the drive shaft is more reliable and has an increased life span. Additionally, the overall spacing from the fly wheel to the outer surface of coupler may sometimes be reduced, which may also allow smaller saw dimensions for example a narrower saw that can more easily pass through restricted openings. Smaller dimensions may also permit use of larger engines with more horsepower, for a given size of equipment, which may translate into better operation and sometimes faster turnaround times. Additionally, by separating the support function from the drive function, driving the load may sometimes be more efficient, which may translate to more horsepower being applied to the load or work piece. Furthermore, manufacturers may be given more flexibility in selecting materials and components for the various parts of the assembly.  
      Once assembled on an engine or other motion producing device, for example an engine of a saw, the sheave  112  is coupled to and rotates with the drive element  68 , and therefore the crank shaft. The bell housing, mounted to the engine block, and therefore the housing tube  108  is stationary relative to the engine block and the sheave is supported by the bearings on the housing tube  108 . The drive shaft  82  extends along the axis  100  and housing tube is coaxial with the drive shaft. The sheave  112  rotates with the drive shaft about the axis  100  while being supported by the housing tube, through which the drive shaft  82  extends. The coupler transfers the rotational motion of the drive shaft  82  into rotational motion in the sheave  112 .  
      Having thus described several exemplary implementations of the invention, it will be apparent that various alterations and modifications can be made without departing from the inventions or the concepts discussed herein. Such operations and modifications, though not expressly described above, are nonetheless intended and implied to be within the spirit and scope of the inventions. Accordingly, the foregoing description is intended to be illustrative only.