Abstract:
Apparatuses and methods are provided for preventing damage to a lawnmower engine and crankshaft when the lawnmower cutting blade encounters an obstructive object. A cutting device for a lawnmower is provided and can include an elongate base member, at least one cutting element pivotably attached to the elongate base member, and a biasing mechanism that engages the cutting element and elongate base member. The at least one cutting element can include a blade portion and a drive engagement portion. The cutting element can pivot when the blade portion strikes an obstructive object such that the blade portion absorbs the impact and retracts to form a blunt shape to prevent damage to the cutting element. The pivoting of the cutting element causes the drive engagement portion to disengage from the crankshaft of the lawnmower to prevent damage thereto.

Description:
TECHNICAL FIELD 
   The subject matter disclosed herein relates generally to apparatuses and methods for preventing damage to a lawnmower engine and crankshaft when a lawnmower cutting blade encounters an obstructive object. More particularly, the present subject matter relates to providing retractable blade cutting apparatuses and methods where a cutting blade can disengage from the crankshaft when the cutting blade strikes an object. 
   BACKGROUND 
   Lawn mowing machines include cutting blades that are attached to a shaft, such as a crankshaft, within the mowing machines that rotate at high speeds for cutting grass. In operation, a mowing machine engine powers the crankshaft to rotate, which in turn rotates the cutting blade that is secured to the crankshaft. Thus, the crankshaft can become damaged when the cutting blade encounters or strikes an obstructive object, for example a rock, because rotation of the blade is interrupted and in some instances the object can completely prevent rotation of the blade and the crankshaft. Meanwhile, the engine continues to attempt to overcome this force, which can lead to damage to the engine and overheating. Furthermore, the crankshaft can become bent after striking an object such as a rock, which requires straightening by a technician that leads to lawn mower downtime. 
   Previous solutions to such problems have included attaching breakaway or yieldable blade tips to a cutting blade in a fixed manner to the rotating crankshaft. Although these blade tips may yield to an obstructive object, the blade tips continue to repetitively strike the object, thereby causing damage to the blade tips that can make the blade tips dull. Also, the cutting blade is still fixed to the rotating shaft in an unyielding manner, thereby continuing to strain the engine as it continues to attempt to overcome the resistive force applied by the object. 
   Therefore, it would advantageous to employ a cutting device that includes a cutting blade coupled with a base member such that the cutting blade can retract within the base member to form a blunt object when striking an object to prevent damage to the blade tip. The cutting blade can also pivotably disengage from the crankshaft when the cutting blade retracts to thereby prevent strain on the crankshaft to avoid overheating and damage to the mower engine. 
   SUMMARY 
   According to one aspect, a cutting device for a mowing machine can comprise an elongate base member. The cutting device can further comprise at least one cutting element pivotably attached to the elongate base member and can have a blade portion and a drive engagement portion. A biasing mechanism engages the blade portion and the elongate blade housing. 
   According to another aspect, a mowing machine can comprise a prime mover and a cutting device having at least one cutting element and an elongate base member. The elongate base member can include a first end, a second end, and an intermediate portion wherein the intermediate portion can define an aperture for receiving a shaft and further wherein the first end and second end both can have upper and lower lips that define a recess. The at least one cutting element can have a blade portion and a drive engagement portion and wherein the at least one cutting element is pivotably attached to the intermediate portion of the elongate base member and the blade portion is disposed within the recesses of elongate base member at the first end and the second end and further wherein the drive engagement portion is configured to rotatably engage the shaft. A biasing mechanism engages the blade portion and the elongate blade housing within the recesses such that the blade portion retracts into the recess when the blade portion strikes an obtrusive object, which thereby causes the cutting element to pivot with respect to the elongate base member, resulting in disengagement of the drive engagement portion from the shaft to prevent damage to the shaft while in rotation. 
   Methods are also provided for preventing damage to a mowing machine shaft during rotation of the shaft when a blade rotatably coupled to the shaft encounters an obstructive object. The methods generally comprise providing a mower housing having a prime mover attached to the mower housing for propelling the mowing machine and providing a cutting device rotatably attached to a shaft of the mowing machine. A handle can be attached to the mower housing. The cutting device provided can include an elongate base member and at least one cutting element pivotably attached to the elongate base member and having a blade portion and a drive engagement portion. A biasing mechanism engages the blade portion and the elongate base member. The methods further can comprise operating the mowing machine to cut grass wherein the at least one cutting element pivots when the blade portion strikes a large object, thereby causing the drive engagement portion of the cuffing element to disengage the shaft and preventing damage to the blade portion and mowing machine. 
   It is therefore an object of the present disclosure to provide retractable blade cutting device apparatuses and methods for preventing damage to a cutting blade and driving mechanism of a mowing machine, such as a crankshaft, when the cutting blade encounters an obstructive object. 
   An object having been stated hereinabove, and which is achieved in whole or in part by the subject matter disclosed herein, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full and enabling disclosure of the present subject matter including the best mode thereof to one of ordinary skill in the art is set forth more particularly in the remainder of the specification, including reference to the accompanying figures in which: 
       FIG. 1  illustrates a perspective view of a mowing machine including an aspect of a cutting device provided in accordance with the subject matter disclosed herein; 
       FIG. 2  illustrates a cross-sectional plan view of an embodiment of a cutting device in a fully engaged position according to the present subject matter; 
       FIG. 3  illustrates a cross-sectional plan view of an embodiment of a cutting device in a partially engaged position according to the present subject matter; 
       FIG. 4  illustrates a cross-sectional plan view of an embodiment of a cutting device in a fully disengaged position according to the present subject matter; 
       FIG. 5  illustrates a cross-sectional view of the embodiment of the cutting device in a fully engaged position according to  FIG. 2 ; 
       FIG. 6  illustrates a cross-sectional view of the embodiment of the cutting device in a partially engaged position according to  FIG. 2 ; and 
       FIG. 7  illustrates a cross-sectional side view of the lower section of a mowing machine with a cutting device attached thereto according to the present subject matter. 
   

   DETAILED DESCRIPTION 
   Reference will now be made in detail to presently preferred embodiments of the present subject matter, one or more examples of which are shown in the figures. Each example is provided to explain the subject matter and not as a limitation. In fact, features illustrated or described as part of one embodiment can be used in another embodiment to yield still a further embodiment. It is intended that the present subject matter cover such modifications and variations. 
   Referring now to  FIG. 1 , a self-propelled lawn mowing machine generally designated LM having a cutting device disclosed generally designated as  20  is illustrated in phantom by way of example. Lawnmower LM can comprise any suitable configuration generally known to persons skilled in the art or later developed. In one aspect, lawnmower LM can comprise a housing such as a mower deck MD, which can include a front portion, a rear portion, an upper exterior portion, and a lower, interior portion. A handle generally designated H can be coupled to the rear portion of mower deck MD by any suitable structure, and can extend upwardly therefrom at an angle appropriate for comfortable grasping and manipulation by an operator. Handle H provides an area to be gripped by an operator and includes a proximal end section, generally designated  12 , which can be the section farthest away from the main operational components of lawn mower LM, such as prime mover or motor M and transmission T. In one aspect, proximal end section  12  of handle H can be generally U-shaped. 
   Mower deck MD can be supported for rolling movement over a surface by a set of wheels and can include one or more idle (non-driving) wheels, such as wheels W, and one or more driving wheels, such as driving wheels WD. There is no limitation as to which one or more of wheels W functions as driving wheel or wheels WD, although typically the rearmost wheel or wheels serve this function. 
   Lawnmower LM can also include a powered drive system or assembly. The powered drive system can include any suitable prime mover such as motor M, which can be an electric motor or an internal combustion engine. The drive system can further include a transmission T illustrated in phantom in  FIG. 1 . Both motor M and transmission T can be mounted to the upper exterior portion of mower deck MD in a suitable manner. As shown in  FIGS. 1 and 7 , a driven member such as a crankshaft  14  or any other suitable output shaft of motor M can rotate cutting device  20  and can be disposed within the interior portion of mower deck MD. Cutting device  20  can be axially restrained on crankshaft  14  by a flanged bolt B (shown in  FIG. 7 ) secured to crankshaft  14 . For example, an end of crankshaft  14  can have a threaded bore therein in which a threaded stem of flanged bolt B can be screwed. 
   Motor M also can transfer power to driving wheels WD through transmission T in any suitable manner, thereby rendering lawnmower LM self-propelled in response to control by an operator. Torque from crankshaft  14  can, for example, be transferred to an input shaft (not shown) of transmission T via an endless belt (not shown). Torque from the input shaft can be transferred to an additional output shaft (e.g., an axle or half-shaft coupled to respective driving wheels WD) through an appropriate reducing or transfer means such as a gear set (not shown). Transmission T can be a variable-speed transmission. 
   The different types, structures, and functions of components of lawnmower LM in addition to those described above are known to persons skilled in the art, and therefore are not further described. 
   Referring now to  FIGS. 1-4 , cutting device  20  having a construction in accordance with the present disclosure is illustrated by way of example. In one aspect, cutting device  20  can include an elongate base member  40  and a plurality of cutting elements or blades  80 . In another aspect, cutting device  20  can include elongate base member  40  and a plurality of cutting blades  80  that can be constructed to perform in accordance with the present disclosure. Elongate base member  40  can be constructed of a rigid plastic material. Cutting blades  80  can be constructed of a metal material, ceramic material, or any other suitable material. 
   As shown in  FIGS. 2-4 , elongate base member  40  can have a first end generally designated  42 , a second end generally designated  44 , and an intermediate portion generally designated  46 . Elongate base member  40  can also include an aperture generally designated  48  for receiving a crankshaft  14 . Aperture  48  can be defined by intermediate portion  46  and can be substantially centered between first end  42  and second end  44 . Intermediate portion  46  can be substantially elongate and can be integral with first and second ends  42 ,  44 . Intermediate portion  46  can also include a plurality of pivoting mechanisms  50  for facilitating a pivoting motion by cutting blades  80  when pivotably attached to elongate base member  40 . Pivoting mechanisms  50  can include screws, bolts, pins, rivets or any other suitable mechanism for facilitating a pivoting action. 
   In one aspect, first and second ends  42 ,  44  can be positioned on opposite ends of intermediate portion  46  and can be substantially identical. In one aspect, first and second ends  42 ,  44  can be club-shaped, that is that first and second ends  42 ,  44  are shaped similarly to the head of a golf club driver. First and second ends  42 ,  44  can have a front blade section generally designated  52  and a rear section generally designated  54 . Rear section  54  can be shaped for providing balance to cutting device  20  so that as cutting device  20  rotates at a high speed it remains balanced due to centrifugal force. Rear section  54  can also be fin-shaped as shown in  FIGS. 5 and 6  to improve lift for standing the grass blades to an erect position so that cutting blades  80  are perpendicular to the grass blades at the moment the grass blades are cut. By improving lift, cutting blades  80  can be slowed, which in turn can reduce noise emission levels. First and second ends  42 ,  44  can be any suitable shape for housing cutting blades  80  or for mounting thereto. 
   As illustrated in  FIGS. 5-6 , front blade section  52  can have an upper lip  56  and a lower lip  58  that can extend beyond upper lip  56 . In other aspects, upper lip  56  and lower lip  58  can extend the same distance or upper lip  58  can extend beyond lower lip  58  such that a blunt surface is created when cutting blades  80  pivot into a retracted position. Any suitable design or shape for first and second ends  42 ,  44  that can create a blunt shaped face can be utilized. Upper lip  56  and lower lip  58  can define an elongated recess generally designated  60  for at least partially housing cutting blades  80 . Elongate recess  60  can extend into intermediate portion  46  such that cutting blades  80  can pivot within elongate base member  40 . 
   As shown in  FIGS. 2-4  and  7 , cutting blades  80  can be encapsulated within elongate base member  40 . The hatched portion represents the solid portion of elongate base member  40  and the non-hatched portion represents elongate recess  60 , which can extend from first and second ends  42 ,  44  through intermediate portion  46  to aperture  48 , whereby drive engagement portion  86  can extend into aperture  48  to matingly engage crankshaft  14 . In this aspect, cutting blades  80  can be substantially encapsulated within elongate base member  40  except for a small portion of cutting blades  80 , as discussed below. These top-down cross-sectional views eliminate the portions of elongate base member  40  that extend over cutting blades  80  according to this aspect. According to this aspect, cutting blade  80  is sandwiched between a top side  70  and a bottom side  72  of elongate base member  40 , as illustrated in  FIGS. 5-7 . 
   In another aspect, cutting blades  80  can be positioned on top of or underneath elongate base member  40  provided that cutting blades  80  can retract to a position such that no portion of cutting blades  80  extends beyond elongate base member  40 . For example, if the illustrations in  FIGS. 2-4  were not cross-sectional views, then cutting blades  80  would be positioned on top of elongate base member  40  such that in a plan view of this particular embodiment cutting blades  80  would be entirely visible, as opposed to simply the cutting portion of cutting blades  80  as shown in  FIGS. 2-4  and  7 . 
   Cutting blades  80  can be pivotably attached to elongate base member  40  with pivoting mechanisms  50 . Cutting blades  80  can have a blade portion  82 , a middle portion  84 , and a drive engagement portion  86 . Cutting blades  80  can be substantially shaped like a butcher&#39;s knife, or any other suitable shape, with blade portion  82  being wide and middle portion  84  being elongate. Drive engagement portion  86  can be shaped like a hook or any other suitable design for matingly engaging crankshaft  14 . Crankshaft  14  can include notches or any other suitable configuration for receiving drive engagement portion  86 . Cutting blades  80  can be pivotably attached to elongate base member  40  at points on middle portion  84  that are proximate aperture  48 . Blade portion  82  can have a beveled end  88  that is sharpened for efficiently and effectively cutting blades of grass. 
   In one aspect, cutting blades  80  can be used wherein drive engagement portions  86  are linked in some suitable manner such that disengagement of multiple blades can occur simultaneously. In another aspect, a single blade can be used such that cutting device  20  is no longer rotatably coupled to crankshaft  14 . In other aspects of the present disclosure, multiple blades can be used with each having drive engagement portions  86  to be matingly coupled to crankshaft  14  such that each blade can separately disengage therefrom. 
   For each of the cutting blades  80 , a biasing mechanism  100  can extend between and contact blade portion  82  of cutting blade  80  and elongate base member  40  within elongate recess  60  of first and second ends  42 ,  44 . Biasing mechanism  100  can be used to bias blade portion  82  of cutting blade  80  to extend beyond upper lip  56  and lower lip  58  such that blade portion  82  is positioned to effectively cut blades of grass in a cutting position. In one aspect, biasing mechanism  100  can be implanted within elongate base member  40  to extend through elongate recess  60  to attach to cutting blade  80 . Biasing mechanism  100  can be a spring or any other suitable structure for biasing cutting blade  80  to extend beyond upper lip  56  and lower lip  58 . Biasing mechanism  100  can be compressible such that cutting blade  80  can retract within elongate recess  60  when cutting blade  80  strikes a resistive object such that cutting blade  80  is in a non-cutting position. The tension strength of biasing mechanism  100  can be adjusted such that the strength is commensurate with the expected forces that are associated with the aforementioned problems. 
   Cutting blades  80  can be interchangeable and replaceable. Thus, biasing mechanism  100  can be fixed to cutting blade  80  in a manner that permits detachment from one another, wherein a new cutting blade  80  could be attached to biasing mechanism  100 . Alternatively, biasing mechanism  100  can be permanently affixed to cutting blade  80  and removably detachable from elongate base member  40 . In another aspect, biasing mechanisms  100  can be permanently fixed to cutting blades  80  and elongate base member  40 . It is envisioned that cutting device  20  can be completely replaced with a replacement cutting device  20  when cutting blades  80  become worn or damaged. In one aspect, flanged bolt B can be removed to permit cutting device  20  to be removed from engagement with crankshaft  14 . A replacement cutting device  20  can then be positioned on crankshaft  14  and secured with flanged bolt B to provide a new cutting device  20  having newly sharpened cutting blades  80 . Alternatively, elongate base member  40  can be constructed of multiple parts such that elongate base member  40  can be disassembled and cutting blades  80  can be removed and then replaced with new replacement cutting blades  80 , after which elongate base member  40  can be reassembled. 
   As illustrated in  FIG. 7 , cutting device  20  can be rotatably coupled to crankshaft  14  of lawnmower LM. In this aspect, one of the two cutting blades  80  is illustrated and is shown partially in phantom such that cuffing blade  80  is encapsulated within elongate base member  40  and beveled edge  88  of cutting blade  80  extends from elongate recess  60  for cuffing blades of grass. Bolt B can axially restrain cutting device  20  on crankshaft  14 . Crankshaft  14  matingly receives drive engagement portion  86  of cutting blade  80 . Front blade section generally designated  52  and rear section generally designated  54  can be seen in this embodiment and face opposite directions such that both ends can cut blades of grass during rotation of cutting device  20 . 
   In operation, cutting device  20  can matingly engage crankshaft  14  by having crankshaft  14  receive drive engagement portion  86  of cutting blades  80 , as shown in  FIG. 2 , such that cutting device  20  can rotate about crankshaft  14  in a grass cutting mode when motor M and transmission T transfer torque to crankshaft  14 . When cutting device  20  is in a grass cutting mode, cutting blades  80  can be biased by biasing mechanism  100  such that beveled end  88  of blade portion  82  of cutting blades  80  extends beyond upper lip  56  and lower lip  58  of first and second ends  42 ,  44  of elongate base member  40 , as illustrated in  FIG. 5 . Cutting blades  80  can therefore rotate at a high speed to cut blades of grass in a cutting position. 
   When blade portion  82  of each cutting blade  80  strikes an obstructive object (e.g., a rock), each cutting blade  80  can absorb the impact and retract within elongate recess  60  in a direction A 2  such that biasing mechanism  100  is in a compressed state and beveled end  88  can be retracted to a position wherein beveled end  88  does not extend beyond upper lip  56  and lower lip  58 , as shown in  FIGS. 3 ,  4  and  6 , thereby creating a blunt shape to strike the object wherein cutting blade  80  moves from a cutting position to a non-cutting position. The action of blade portion  82  retracting into elongate recess  60  can cause the corresponding cutting blade  80  to pivot at pivoting mechanism  50  positioned on intermediate portion  46  of elongate base member  40 . Simultaneously, the drive engagement portion  86  of the cutting blade  80  is pivoted away from crankshaft  14  in direction A 1 , as shown in  FIG. 3 , thereby disengaging the cutting blade  80  and cutting device  20  from crankshaft  14 . The other cutting blade  80  that is not encountering the obstructive object can remain engaged to crankshaft  14  until it encounters the same obstructive object during the same rotation of cutting device  20 , and upon encountering the object can pivot and retract in the same manner. 
   After mower deck MD passes the obstructive object or blade portion  82  rotates past the object, biasing mechanism  100  can force blade portion  82  and beveled end  88  out of elongate recess  60  such that beveled end  88  once again extends beyond upper lip  56  and lower lip  58 , resulting in lawnmower LM operating in a cutting mode wherein cutting blade  80  is in a cutting position. Simultaneously, cutting blade  80  can pivot at pivoting mechanism  50  to permit drive engagement portion  86  of cutting blade  80  to re-engage crankshaft  14 , for example the hooks of drive engagement portion  86  being received within the notched section of crankshaft  14 , thereby facilitating rotation of cutting device  20  about crankshaft  14  within mower deck MD. 
   As illustrated in  FIG. 4 , it is also possible for drive engagement portions  86  can be disengaged from crankshaft  14  simultaneously such that cutting device  20  is no longer rotatably coupled to crankshaft  14 , causing cutting device  20  to free spin and slow until rotation of cutting device  20  is terminated. 
   It will be understood that various details of the disclosed subject matter may be changed without departing from the scope of the disclosed subject matter. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation.