Abstract:
A concrete saw for cutting concrete and other hard surfaces or substrates. The concrete saw includes a multispeed drive for transmitting power from the saw&#39;s engine to the saw&#39;s cutting blade. The multispeed drive includes a flexible belt for transmitting rotational energy from the drive shaft of the engine to the drive shaft for the blade, and a releasable tension device for placing tension on the belt and ensuring good engagement between the sprockets of the drive shafts. Upon release of the tension device, a user may move the belt to an alternate position on the sprockets and retension the belt, thereby providing a different drive ration and speed for the cutting blade at a constant engine speed.

Description:
FIELD OF THE INVENTION 
     The present invention is related to an internal combustion powered saw for cutting concrete, stone, asphalt and other similar surfaces, and in particular, to a concrete saw equipped with a multispeed drive system. 
     BACKGROUND OF THE INVENTION 
     In the concrete industry, when building bridges, buildings, roads and the like, it is often necessary to pour large horizontal slabs of concrete. Once poured, it is usually necessary to machine the slab. Such machining may include cutting seams completely through the slab (to form expansion joints and to allow for foundation shifting), cutting notches partially into the slab (to create stress cracks along which the slab will split), cutting multiple grooves into the slab to create a high friction surface such as for bridges, grinding the surface of the slab and the like. Various types of concrete saws may be utilized to carry out these machining tasks. In larger industrial applications, large self-propelled saws are used which are powered in a variety of manners, such as by gasoline, diesel, electric, propane and natural gas engines mounted on the saw. While performing a cut, the operator walks behind the saw to control the direction, cutting speed, cutting depth and the like. 
     Typical self-propelled concrete saws are mounted upon rear drive wheels and upon a hinged front axle assembly which raises and lowers the front end of the saw. The front axle assembly includes a height adjustment cylinder that is attached to a front axle assembly having the front wheels thereon. The front axle assembly pivots downward away from, and upward toward, the saw frame when the cylinder extends and retracts thereby raising and lowering the saw. The saw blade is mounted upon a blade support shaft proximate the front of the saw and thus as the front end is raised and lowered, the cut depth is varied. 
     Conventional concrete saws include a gasoline, diesel, propane (internal combustion), hydraulic and air or electric engine aligned along an axis transverse to the longitudinal axis of the saw frame. This transverse arrangement aligns the engine crankshaft parallel to the rotational axis of the saw blade, to afford an easy design for interconnecting pulleys upon the crankshaft and the saw blade. 
     Conventional internal combustion (nonelectric) powered concrete saws utilize a mechanical governor for controlling the RPMS (revolutions per minute) of the engine and the saw blade. Every type of saw blade operates at a different optimal rotational speed. The optimal speed for a given blade is maintained by using a specific pulley size to blade size ratio. This requires changing the pulleys in the drive system to accommodate specific blade sizes. If optimal speed is not maintained, engine power is lost and blades can be damaged. Most nonelectric powered concrete saws are designed to operate with a plurality of blade sizes and they are capable of rotating at extremely high speeds. 
     Most prior art internal combustion saws only operate at one cutting blade speed. Because different saw blades operate at peak performance at different rotational speeds, saw performance is limited due to a single speed drive system. Thus, there is a need to vary blade speed based on the particular blade being used or the sawing conditions encountered. The prior art provides multispeed drive systems for concrete saws. However, such saws rely on complex, costly and/or limited service life transmissions or hydraulic drive systems. Some hydraulic systems require water cooling that prevents use of the saw for dry cutting operations. Also, in some prior art multispeed machines, the pulleys are so large that they interfere with a saws ability to make a cut of acceptable depth. Thus, the need exists for an internal combustion powered concrete saw capable of operating at different rotational cutting speeds having a dependable and simple multispeed drive system. 
     SUMMARY OF THE INVENTION 
     The present invention provides a new and improved saw for cutting concrete, asphalt, stone and other hard or tough surfaces. The saw of the present invention includes a multispeed drive that allows an operator or user to easily vary the speed of the cutting blade, thereby helping to facilitate optimum cutting speeds and performance. 
     In a preferred embodiment, the saw of the present invention includes a multispeed drive for transmitting power from the engine to the cutting blade. The multispeed drive includes a flexible belt for transmitting rotational energy from the drive shaft of the engine to the drive shaft for the blade, a releasable tension device for placing tension on the belt and ensuring good engagement between the sprockets of the drive shafts. Upon release of the tension device, a user may move the belt to an alternate position on the sprockets, and retension the belt, thereby providing a different drive ratio and speed for the cutting blade and at a constant or set engine speed. The belt preferably includes a series of teeth along its inner diameter or surface. 
     The foregoing and other features of the invention are hereinafter more fully described and particularly pointed out in the claims, the following descriptions setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principals of the present invention may be employed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a side view of a saw made in accordance with the present invention; and 
     FIG. 2 is a perspective exploded view of the multispeed drive system of the saw shown in FIG. 1; 
     FIG. 3 is a top view of a portion of the multispeed drive system of FIG. 2; 
     FIG. 4 is a side view of the portion of the multispeed drive system shown in FIG. 3; 
     FIG. 5 is another side view of the portion of the multispeed drive system shown in FIG. 3 in the engaged position; and 
     FIG. 6 is a schematic representation of an alternate form of a tensioning device assembly for use in a multispeed drive system made in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, and initially to FIG. 1 there is shown a saw  10  for cutting concrete, asphalt, stone and other hardened surfaces made in accordance with the present invention. Saw  10  includes a blade  12 , an engine  14 , a frame  16  and a set of front  18  and rear  20  wheels. Saw  10  is preferably a self-propelled saw, and thus the rear wheels  20  are driven in a conventional manner (e.g., a hydraulic drive system). However, it will be appreciated that saw  10  could be a push-type saw. 
     Referring now additionally to FIGS. 2-5, the details of the multispeed drive system  30  are more clearly illustrated. System  30  includes a drive or jack shaft  32  supported at each end by bearings  33  for transmitting power across the front of the saw  10  and to the blade  12 . Shaft  32  includes at one end a multi-sheave pulley  34  for driving V-belts  36  and multi-sheave pulley  35 . Pulley  35  is connected by shaft  39  to blade  12 . Located at the fore end of shaft  32  is a sprocket assembly  40  comprising a pair of sprockets  42  and  44 . Sprockets  42  and  44  are of different diameters. 
     Provided on the output shaft  46  of engine  14  is a sprocket assembly  47  comprising a pair of sprockets  48  and  50 . Sprockets  48  and  50  are of different diameters. Extending between the sprocket assemblies  40  and  47  is a flexible belt  52 . Belt  52  includes a plurality of teeth extending along the inside surface or diameter  54  of belt  52 . The teeth of belt  52  engage the teeth formed along the outer diameter of the sprockets  42 ,  44 ,  48  and  50 . 
     Located between sprocket assemblies  40  and  47  is a releasable tensioning unit or assembly  56 . Tension assembly  56  includes an idler sprocket  58  which is supported for rotation upon idler arm  60  by axle screw  61  and bearings  63 . Idler arm  60  is supported upon idler block  65  that is mounted to the frame  16  of the saw  10 . Idler arm  60  is supported for pivotal rotation on idler block  65  by capscrew  64  and bearing  66 . Assembly  56  also includes tension arm  70  that is pivotally mounted to tensioner mount block  73  by screw  74  and bearing  75 . Mount block  73  is also mounted to the frame  16  of the saw  10 . Tension arm  70  includes a tensioning screw  80  that may be adjusted (threaded) up and down relative to platform  83 . As the end of screw  80  engages tab  82  of idler arm  60 , sprocket  58  is pushed harder against the inner surface  54  of belt  52 , thus putting greater tension on the belt  52 . 
     Idler arm  60  includes a handle  86 . Handle  86  allows a user to pull on idler arm  60  and place greater tension on belt  52 . While pulling on handle  86 , tension is released as between the end of screw  80  and tab  82  and thus a user can flip the tension arm  70  back and out of engagement with tab  82 . This allows idler arm  60  to swing down out of engagement with belt  52  and into the position shown in FIG. 4, relieving all tension on belt  52 . In the untensioned mode, belt  52  can move freely and easily along sprocket assemblies  40  and  47 , allowing the user to select the specific diameter of sprocket desired as best seen in FIG. 3, thereby altering the drive rate for the cutting blade  12 . A user can then retension the belt  52  by pulling on handle  86  and flipping tension arm  70  up such that the end of screw  80  engages tab  82 . Screw  80  can then be adjusted to produce the desired tension. Of course, it will be appreciated that sprocket assemblies  40  and  47  may comprise more than the illustrated two sprockets of differing diameter. Depending upon the bearing load limits of engine  14  and space constraints, three or more sprockets of differing diameter could be utilized. Of course, it will also be appreciated that sprocket assemblies  40  and  47  could be formed of a single piece. 
     Belt  52  may comprise any number of conventionally available toothed flexible rubber belts. However, a preferred belt is a POLYCHAIN® synchronous belt available from the Gates Rubber Company. Such synchronous belts resist slipping and they normally do not require continual retensioning. This type of belt does an excellent job of transferring energy. One synchronous belt can do the job of many V-belts thereby saving valuable space. The use of a synchronous belt affords several advantages over conventional V-belts. For example, synchronous belts operate at zero slip and they do not require near the load that V-belts require for proper tensioning. Lower tension levels reduce load levels on shafts, thereby helping to extend bearing life. Engine crankshafts are especially sensitive to high tension loads. High belt tension loads create a bending effect upon the crankshaft which reduces engine life. Generally, engines are designed with light shell type bearing to support the crankshaft. These shell type bearings are not capable of withstanding major side loads over a substantial period of time. The use of a synchronous belt, that requires minimal tensioning, avoids all of the excessive loading issues presented by V-belts. 
     The ability to quickly and easily alter the cutting speed of the blade provides a distinct advantage. Specifically, it allows a user to quickly match the cutting speed to the particular blade being used and/or specific sawing conditions. Depending upon the condition of the surface being cut, a slower or faster cutting speed at a particular engine rpm can be desired. 
     The particular configuration of the present drive system  30  provides several distinct advantages. First, the configuration provides for engagement along the inner surface  54  of belt  52 , thereby saving room and thus minimizing the size of the drive system  30 . Also, in the present design the V-belts  36  are at the end of jack shaft  32  thereby facilitating the replacement of such belts. The configuration also allows one to use small pulleys to drive the V-belts  36 , thereby facilitating good cutting depths. Use of the jack shaft  32  that extends across the width of the saw  10 , along with V-belts  36  and toothed belt  52  also provides an advantage. Specifically, such arrangement minimizes the width of the saw, reduces loads on the engine bearings, and because it employs V-belts  36  it allows for slip in the event that the blade  12  becomes trapped or stalled. With this particular arrangement, because pulley and sprocket sizes are so small, one could easily mount the jack shaft on the engine itself (e.g., the engine base or frame) thereby saving additional room and making the tensioning of the V-belts very simple. 
     Referring now to FIG. 6, there is schematically illustrated another embodiment of a tension assembly made in accordance with the present invention. In FIG. 6, the same numerals have been used to identify elements that are common to FIGS. 1-5. Also, in FIG. 6 only the inner sprockets  42  and  48  are shown for sake of simplicity. In FIG. 6 the tension device assembly  99  includes a handle  86 , a smooth surfaced idler roller or sprocket  100  engaging the outer surface  101  of toothed belt  52 , an idler arm  102 , and an idler block or support  108  mounted to the saw frame  16 . Roller  100  rotates freely on screw and bearing assembly  107  that is attached to arm  102 . Assembly  99  also includes a bolt  109  that can be loosened with a wrench to allow arm  102  to pivot freely, or tightened to lock arm  102  into position. Upon loosening of bolt  109 , a user can swing arm  102  out of engagement with belt  52  thereby allowing a user to change the position of the belt on the sprockets. Using handle  86 , a user can then push roller  100  into engagement with belt  52  to apply the desired tension, and then tighten bolt  109  and arm  102  into position. Of course, it will be appreciated that in the embodiments shown in FIGS. 1-6, any one of a variety of means may be employed to hold the idler arm in place. For example, a hydraulic cylinder or spring could be utilized to apply the required force on arm  102  or arm  60 . 
     While the invention has been shown and described with respect to a specific embodiment thereof, this is for the purpose of illustration rather than limitation, and other variations and modifications of the specific device herein shown and described will be apparent to those skilled in the art all within the intended spirit and scope of the invention. Accordingly, the patent is not to be limited in scope and effect to the specific embodiments herein shown and described, nor in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention.