Patent Publication Number: US-10306835-B2

Title: Rear discharge mower deck

Description:
TECHNICAL FIELD 
     This invention relates to the field of lawn mowers and, more particularly, to a multi-bladed, rear discharge mower deck for connection to a self-propelled traction unit, such as the frame of a riding mower. 
     BACKGROUND OF THE INVENTION 
     Many lawn mowers are known which comprise a self-propelled traction unit of some type, such as the frame of a riding mower. Many of these mowers carry a multi-bladed rotary cutting deck having a plurality of blades that rotate in substantially horizontal cutting planes to cut grass over a relatively wide swath as the mower makes a single pass over the ground. Such cutting decks often utilize three cutting blades arranged in a staggered configuration comprising a forward central cutting blade flanked on each side by trailing side cutting blades. Such a fore-and-aft staggered configuration allows the deck to cut an unbroken swath of grass during forward motion of the mower without there being any danger of the blades hitting one another. 
     In many cases, such multi-bladed cutting decks have used cutting blades that are the same as each other and that rotate in the same direction, i.e. all towards the left side of the deck or the right side of the deck. In many cases, such decks have had a discharge opening arranged on the side of the deck towards which the clippings were directed by the blades to allow the clippings to be thrown outwardly past the side of the deck. However, such a blade arrangement does not work well in a rear discharge deck where one desires that the clippings be thrown out to the rear of the deck through a rear discharge opening. In such a case, the unidirectional rotation of all the cutting blades causes the grass clippings to be thrown out to the rear in a windrow along one side of the deck. This is not aesthetically pleasing and additionally prevents the grass clippings from breaking down into mulch as quickly as they would have broken down had such clippings been more evenly distributed over the cut grass swath. 
     Various attempts have been made to improve the distribution of clippings to the rear when a rear discharge opening is provided on a mower deck. However, many such attempts have embodied fairly complicated baffling structure on the underside of the mower deck to create entirely separate flow paths for the grass clipping streams generated by the various cutting blades. While this may in some cases cause a more even distribution of clippings, the cost of extensive baffling can be expensive to manufacture and maintain. More significantly, the presence of the baffling can affect how well the cutting blades cut the grass in the first place, as unevenly cut streaks of grass might appear along the lines of the baffling or elsewhere. Thus, there is a need in the art for a rear discharge mower deck that accomplishes a more even and uniform distribution of grass clippings across the width of a rear discharge opening while maintaining a high quality of cut. 
     SUMMARY OF THE INVENTION 
     One aspect of this invention relates to a rear discharge mower deck for attachment to the traction frame of a lawn mower. The mower deck comprises a top wall, a front wall, and a pair of side walls forming a downwardly opening space. The space is open along a rear side thereof to form a rear discharge opening through which grass clippings may be discharged. Three rotary cutting blades having substantially vertical spindles are rotatably journalled in the top wall with the cutting blades being positioned beneath the top wall to rotate in horizontal cutting planes within the space defined by the walls to cut grass. The cutting blades comprise a center cutting blade and a pair of side cutting blades that collectively cut a substantially continuous swath of grass during forward motion of the mower deck. The center cutting blade and a first side blade have unidirectional rotation in the same direction as one another and a second side blade counter-rotates in an opposite direction. Two flow deflectors are arranged within the space defined by the walls with a first flow deflector being located generally between the center blade and the first side blade and a second flow deflector being located generally between the center blade and the second side blade. The first and second flow deflectors have cross-sections formed from a pair of side surfaces that join together along an apex. However, the first and second flow deflectors are inverted relative to one another such the apex of the first deflector faces downwardly within the space while the apex of the second deflector faces upwardly within the space. 
     Another aspect of this invention relates to a mower deck for attachment to the traction frame of a lawn mower. The mower deck comprises a plurality of walls forming a downwardly opening space. At least a pair of cutting blades is positioned within the space to rotate in substantially horizontal cutting planes within the space defined by the walls to cut grass. The blades are disposed laterally adjacent to one another within the space and the blades counter-rotate in opposite directions relative to one another. A flow deflector is located within the space generally between the blades. The flow deflector has a pair of side surfaces that join along an apex. The side surfaces of the flow deflector are inclined relative to vertical and the apex of the flow deflector faces upwardly within the space such that one side surface of the deflector intercepts a first air flow and grass clipping stream generated by one blade to redirect the first air flow and grass clipping stream upwardly within the space and the other side surface of the deflector intercepts a second air flow and grass clipping stream generated by the other counter-rotating blade to also redirect the second air flow and grass clipping stream upwardly with the space. 
     Yet another aspect of this invention relates to a rear discharge mower deck for attachment to the traction frame of a lawn mower. The mower deck comprises a top wall, a front wall, and a pair of side walls forming a downwardly opening space. The space is open along a rear side thereof to form a rear discharge opening through which grass clippings may be discharged. Three rotary cutting blades having substantially vertical spindles are rotatably journalled in the top wall with the cutting blades being positioned beneath the top wall to rotate in horizontal cutting planes within the space defined by the walls to cut grass. The cutting blades comprise a center cutting blade and a pair of side cutting blades that collectively cut a substantially continuous swath of grass during forward motion of the mower deck. The center cutting blade and a first side blade have unidirectional rotation in the same direction as one another and a second side blade counter-rotates in an opposite direction. A front flow control baffle extends substantially across the width of the top wall and extends downwardly from the top wall with the front flow control baffle being located between the front wall and the cutting blades. The first side blade has greater clearance between the blade and an immediately adjacent portion of the flow control baffle ahead of the first side blade when the first side blade is in a directly fore-and-aft orientation than a clearance between the center blade and an immediately adjacent portion of the flow control baffle ahead of the center blade when the center blade is in a directly fore-and-aft orientation to decrease the ability of the first side blade to pump or move grass clippings to the center blade to promote more even distribution of grass clippings across the rear discharge opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This invention will be described in detail hereafter in the Detailed Description, when taken in conjunction with the following drawings, in which like reference numerals refer to like elements throughout. 
         FIG. 1  is a perspective view of the top of a rear discharge mower deck according to one embodiment of this invention; 
         FIG. 2  is a bottom plan view of the deck of  FIG. 1 , but with first and second flow deflectors having been omitted from the view to more particularly illustrate the shape of a front flow control baffle; 
         FIG. 3  is a bottom plan view similar to  FIG. 2 , but illustrating the first and second flow deflectors in their installed conditions within the deck; 
         FIG. 4  is a perspective view of the underside of the deck of  FIG. 3 , particularly illustrating a bottom cover for the second flow deflector in an exploded condition relative to the rest of the flow deflector; 
         FIG. 5  is a cross-sectional side elevational view of the deck of  FIG. 3 , particularly illustrating the first flow deflector; 
         FIG. 6  is a cross-sectional side elevational view similar to  FIG. 5 , but particularly illustrating the second flow deflector; and 
         FIG. 7  is a perspective view similar to  FIG. 1 , but particularly illustrating trailing rear shields behind the downwardly and rearwardly inclined side sections of the rear portion of the top wall of the deck. 
     
    
    
     DETAILED DESCRIPTION 
     A mower deck according to one embodiment of this invention is generally illustrated as  2  herein. Deck  2  is suited to be attached in a conventional manner to the self-propelled traction frame of a conventional riding mower. This may be a mower such as the Lazer Z mower which has long been manufactured and sold by Exmark Manufacturing Company, Inc., the assignee of this invention. In the Lazer Z mower, deck  2  is mounted in a mid-mount fashion beneath the frame of a hydraulically driven, zero radius turn mower that carries a seated operator. U.S. Pat. Nos. 5,816,033 and 5,865,020, which are hereby incorporated by reference, describe various aspects of the Lazer Z mower. The traction frame may be of other types as well, such as the Exmark Vantage mower which carries the operator in a standing position atop an operator support platform at the rear of the mower. In addition, deck  2  may be mounted in a forward position on the traction frame, may be a wing deck that is attached to one side of the traction frame, or may be a deck that trails the traction frame and is towed by the traction frame. 
     Deck  2  has a top wall  4  that includes a substantially horizontal front portion  6  and a downwardly inclined rear portion  8 . Top wall front portion  6  has a substantially V-shaped front edge  10  that includes a short central portion  12  that slightly truncates the V-shape of the front edge at the apex of the V-shape. Deck  2  includes a front wall  14  that extends downwardly from top wall front portion  6 . Thus, front wall  14  of deck  2  has the same slightly truncated, substantially V-shaped configuration as front edge  10  of top wall front portion  6 . 
     Top wall  4  of deck  2  further includes a pair of laterally spaced side edges  16 . Side edges  16  extend rearwardly from the corners of front edge  10  of top wall  4  of deck  2  back along the remaining length of front and rear portions  6  and  8  of top wall  4  of deck  2 . Side edges  16  terminate at the rear of deck  2  at the corners of a narrow, substantially horizontal lip  18 . Lip  18  forms the extreme rear end of top wall rear portion  8  of deck  2 . 
     Deck  2  includes side walls  20  that extend downwardly from side edges  16  of top wall  4  except that the rear sections  22  of side walls  20  curve laterally to the inside away from side edges  16 . Curved rear sections  22  of side walls  20  underlie opposite sides of top wall rear portion  8 . There is no rear wall on deck  2  similar to the vertically extending front and side walls  14  and  20  of deck  2 . Each curved rear section  22  terminates in a steeply inclined tip  23  whose height rapidly decreases as tip  23  extends inwardly with such inclination of tip  23  minimizing the tendency of grass clippings to hairpin or catch on the tips  23  of rear ends  22 . The open lateral distance extending between the curved rear sections  22  of side walls  20 , which distance is indicated as w in  FIG. 2  and which distance comprises a substantial majority of the width of top wall rear portion  8  of deck  2 , is left open to form a laterally extending, rear discharge opening  24  for grass clippings. For these purposes, inclined tips  23  are considered to be part of rear discharge opening  24  due to their rapidly vanishing height resulting from their steep inclination and are thus shown as part of the width w of rear discharge opening  24 . 
     Downwardly inclined rear portion  8  of top wall  4  of deck  2  is formed in a plurality of sections  26 . Sections  26  comprise a wide center section  26   c  and two side sections  26   s  that are narrower in width than center section  26   c . Side sections  26   s  adjoin center section  26   c  and are connected to opposite lateral sides of center section  26   c  by triangular, vertically slanted connecting walls  28 . Wide center section  26   c  is longer in a fore-and-aft direction than side sections  26   s  such that center section  26   c  protrudes further forwardly than do side sections  26   s . 
     Substantially horizontal front portion  6  of top wall  4  of deck  2  includes three circular holes therein which will mount the spindles  30  of three rotary cutting blades  32  that are located beneath top wall  4  of deck  2 . As is shown in  FIGS. 1 and 2 , the center hole is located directly in front of wide center section  26   c  of top wall rear portion  8 . The side holes are rearwardly staggered relative to the center hole to be located in advance of side sections  26   s  of top wall rear portion  8  adjacent the sides of the forwardly protruding portion of center section  26   c . Due to this staggered configuration, the cut grass paths of the three cutting blades  32  will overlap slightly across the width of deck  2  to cut a single generally unbroken swath of grass during each pass of deck  2 . Rather than use this staggered blade configuration, it would also be possible to use three cutting blades  32  that are arranged in a straight line side-by-side configuration with the orbits of the side blades overlapping that of the center blade. This alternate blade configuration would require the use of a timed drive system, such as a cogged timing belt, that would prevent the blades from striking one another. 
     The purpose of center section  26   c  and side sections  26   s  forming top wall rear portion  8  is to form rearwardly extending, downwardly inclined ramps to smoothly deflect the grass clippings being generated in the interior of deck  2  by cutting blades  32  in a downward direction as such clippings flow rearwardly towards and eventually through rear discharge opening  24  of deck  2 . Center section  26   c  and side sections  26   s  all terminate along their rear edges at the same vertical elevation. This is an elevation corresponding to the elevation of lip  18  that forms the terminus of top wall rear portion  8  of deck  2 . The elevation of lip  18  is above the elevations of the lower edges of front and side walls  14  and  20  of deck  2 . See  FIGS. 5 and 6 . Given the different fore-and-aft lengths of center section  26   c  and side sections  26   s , center section  26   c  is less steeply inclined than side sections  26   s . 
     Referring now to  FIG. 2 , cutting blades  32  do not all rotate in the same direction. The center blade  32   c  and one side blade  32   s1  rotate in one direction as indicated by the arrows A when deck  2  is viewed from the underside. The other side blade  32   s2  rotates in an opposite direction as indicated by the arrow B when deck  2  is viewed from the underside. These directions of rotation are achieved by a conventional belt and pulley drive system (not shown) located above top wall  4  of deck  2 . This drive system rotates the tops of spindles  30  of cutting blades  32  in the appropriate directions to achieve the directions of blade rotation shown in  FIG. 2 . Other alternative drive systems, e.g. gearboxes, hydraulic or electric motors, could be used for achieving blade rotation. 
     A front flow control baffle  34  is provided in the front of deck  2  between front wall  14  of deck  2  and the tips of cutting blades  32 . Front flow control baffle  34  extends vertically downwardly from the underside of top wall  4  of deck  2  to an elevation that is substantially equal to or slightly above the elevation of the substantially horizontal planes in which cutting blades  32  rotate. Front flow control baffle  34  extends across deck  2  with the ends of front flow control baffle  34  being joined to side walls  20  of deck  2 . Front flow control baffle  34  includes three generally rounded or arcuate sections  36  with some straight portions. One baffle section  36  is positioned ahead of and surrounds a substantial portion of the forward half of the circular orbit of the tip of each cutting blade  32 . Adjacent baffle sections  36  of front flow control baffle  34  join with one another to form a pair of substantially vertical, V-shaped apexes  38   a  and  38   b . Arrows C and D in  FIG. 2  pass through apexes  38   a  and  38   b  and have been created in  FIG. 2  by bisecting the angles α and β between the joined portions of each pair of adjacent baffle sections  36  that form the apexes  38   a  and  38   b  such that arrows C and D can be considered to generally illustrate the rearwardly extending direction in which the respective apexes  38   a  and  38   b  are disposed or point. As can be seen in  FIG. 2 , arrows C and D illustrate that apexes  38   a  and  38   b  point toward the midsection of rear discharge opening  24  of deck  2 . 
     Referring to  FIG. 3 , there are two flow deflectors  40  and  50  that are joined to and extend rearwardly from the apexes  38   a  and  38   b  of front flow control baffle  34 . The first deflector  40  comprises a V-shaped structure having two triangular side surfaces  42  that form an apex  44  therebetween. First deflector  40  extends downwardly from top wall  4  of deck  2  such that apex  44  of first deflector  40  faces downwardly. In addition, side surfaces  42  of first deflector  40  progressively decrease in height as first deflector  40  extends rearwardly. Thus, first deflector  40  has its greatest depth within deck  2  where first deflector  40  attaches to front flow control baffle  34  with apex  44  of first deflector  40  rising upwardly as first deflector  40  extends rearwardly due to the decrease in the height of side surfaces  42  of first deflector  40 . For definitional purposes herein, the word apex is intended to mean throughout this application the elongated zone where the surfaces that form the apex come together to be substantially contiguous to or to border one another, whether such zone is formed as a relatively sharp line or edge, or is truncated by a shape such as a curved surface having a radius or as a planar surface, etc. For example, first deflector  40  is preferably formed by bending a piece of sheet metal into the shape that is shown in the drawings such that apex  44  has a small radius at the bend where side surfaces  42  come together. 
     First deflector  40  is attached to front flow control baffle  34  at the apex  38   a  of front flow control baffle  34  that is generally between cutting blades  32   c  and  32   s1  that rotate in the same direction as one another. When so attached, apex  44  of first deflector  40  is aligned with and extends in the same direction as the direction C of apex  38   a  of front flow control baffle  34  to which it is attached, as best shown in  FIG. 3 . In addition, first deflector  40  is fairly long and extends substantially rearwardly so that the rear end of first deflector  40  is closely adjacent to or touches a straight line  46  that connects the centers of rotation of cutting blades  32   c  and  32   s1 . Any portion of first deflector  40  that overlies any of the orbits of cutting blades  32   c  and  32   s1  is obviously vertically spaced above cutting blades  32   c  and  32   s1  to prevent cutting blades  32   c  and  32   s1  from hitting or striking first deflector  40 . The purpose of first deflector  40  will be described in more detail hereafter. 
     Second flow deflector  50  is attached to those portions of front flow control baffle  34  that form the other apex  38   b  of front flow control baffle  34 . Similarly to first deflector  40 , second deflector  50  comprises a substantially V-shaped structure having two side surfaces  52  that form an apex  54  therebetween. Second deflector  50  is truncated at the rear of deflector  50  so that side surfaces  52  of second deflector  50  are polygonal in shape rather than triangular as in first deflector  40 . In addition, second deflector  50  is much shorter in length than first deflector  40 , thus extending far less to the rear as compared to first deflector  40 . Second deflector  50  is short enough in length that it lies entirely outside of the orbits of center cutting blade  32   c  and the counter-rotating side cutting blade  32   s2 . 
     More importantly, second deflector  50  has an inverse orientation compared to the orientation of first deflector  40 . Second deflector  50  is positioned at the bottom of front flow control baffle  34  and is seated in a notch in the lower edge of front flow control baffle  34 . Second deflector  50  extends forwardly past front flow control baffle  34  with a front end of second deflector  50  attaching to the backside of front wall  14  of deck  2 . When so mounted, second deflector  50  actually extends upwardly with apex  54  of second deflector  50  facing upwardly towards top wall  4  of deck  2 . Moreover, second deflector  50  has a maximum height along the other apex  38   b  of front flow control baffle  34  (approximately ⅓ rd  the height of apex  38   b  where second deflector  50  joins apex  38   b ) that is substantially less than the maximum height of first deflector  40  (at least approximately ½ the height of apex  38   a  where first deflector  50  joins apex  38   a ). A cover  56  (as only shown in  FIG. 4  in exploded form) may be used to close off the open bottom and the open truncated rear end of second deflector  50  to prevent grass clippings from collecting inside second deflector  50  and to provide additional structural support. 
     Finally, there is a physical difference between the various cutting blades used in deck  2 . The two blades that rotate in the same direction as one another, namely center blade  32   c  and  32   s , are blades of the type shown in U.S. Pat. No. 6,675,569, which patent is hereby incorporated by reference. The opposite ends of such blades  32   c  and  32   s1  have a relatively high, relatively long, upturned sail  58  that is serrated to provide a plurality of sail sections on the trailing edges of the blades adjacent the tips of the blades, e.g. a sail  58  that is approximately 0.88 inches high for the outer most sail section and 1.125 inches high for each of the three narrower inboard sail sections and 6 inches long for blades having a tip to tip length of 20.5 to 24.5 inches. Such high sails  58  generate a relatively strong circumferential and upwardly directed air flow which helps stand the grass up beneath such blades for cutting. By contrast, the side cutting blade  32   s2  that is counter-rotating in  FIG. 2  is a lower lift blade, namely a blade without any sail on the trailing edges of the blade or with lower and shorter sails  60  compared to the height and length of the sails  58  on the other cutting blades, e.g. a sail  60  that is approximately 0.63 inches high and 2.5 to 4 inches long for blades having a tip to tip length of 20.5 to 24.5 inches. This lower lift blade  32   s2  generates far less in the way of air flow than do the other two blades, though enough to carry the grass clippings generated by the lower lift blade around in a circumferential direction. Other blade designs providing other lower lift and higher lift characteristics may be used in place of blades  32  as described herein. 
     The Applicants have found that a deck  2  constructed as described above and equipped with cutting blades  32  as described above provide improved distribution of the grass clippings through rear discharge opening  24  without any deleterious effect on the cutting performance of deck  2 . In this regard, improved distribution means fairly even distribution of the grass clippings across rear discharge opening  24  to minimize the clippings being more heavily concentrated in particular areas of rear discharge opening  24 . This minimizes undesirable windrowing or clumping of the clippings on top of the cut grass swath. This also allows the clippings to be more evenly dispersed into the cut grass swath for decomposition of the clippings into mulch. While a majority of the clippings will flow down along the downwardly inclined ramp created by center section  26   c  of the rear portion of deck  2  as they pass through rear discharge opening  24 , some of the clippings from the two side cutting blades  32   s1  and  32   s2  will flow down along the ramps created by side sections  26   s  of the rear portion of deck  2  in achieving even distribution of the clippings. 
     With regard to the achievement of a fairly even distribution of the clippings, first deflector  40  helps ensure that the grass clippings generated by the two cutting blades  32   c  and  32   s1  that rotate in the same direction do not all flow substantially around the front portion of center cutting blade  32   c . The Applicants have found that first deflector  40 , being positioned near top wall  4  of deck  2  in the path where the grass clippings tend to flow, intercepts a substantial portion of the grass clippings being generated by the side blade  32   s1  and perhaps some of the grass clippings being generated by the center blade  32   c  and causes such clippings to be directed out through the portions of rear discharge opening  24  on that side of deck  2  in which the side cutting blade  32   s1  is installed. Without such first deflector  40 , the Applicants found that the grass clippings would be less evenly distributed across the width of rear discharge opening  24 , and would be more heavily concentrated towards the side of deck  2  having the counter-rotating side blade  32   s2 . Moreover, referring to  FIG. 3 , the tip of side cutting blade  32   s1  is spaced further away from front baffle  34  (e.g. approximately 2.7 inches indicated by distance ds 1  in  FIG. 3 ) than the tip of center cutting blade  32   c  in a corresponding position relative to front baffle  34  (e.g. approximately 1.5 inches as indicated by the distance d c  in  FIG. 3 ). This approximately 80% increase in the tip to baffle spacing of side cutting blade  32   s1  compared to center cutting blade  32   c  further decreases the ability of side cutting blade  32   s1  to pump or move clippings towards the center of deck  2 , thus working in concert with first deflector  40  in achieving more even distribution of clippings across rear discharge opening  24 . 
     Second deflector  50  also serves a function in helping to redirect the convergence of the air flows and clipping streams generated by the center blade and the counter-rotating side blade  32   c  and  32   s2  where those two air flows and clipping streams would otherwise meet at the other apex  38   b  on front flow control baffle  34 . The second deflector  50  redirects the air flows and clipping streams to reduce the down pressure in this specific area of the deck and allow the uncut grass to remain upright and be cut by the blades  32 . Without second deflector  50 , the Applicants found that the converging air flows and clipping streams in this location from these two cutting blades  32   c  and  32   s2  would tend to leave a streak in the cut grass swath in which the grass was not as precisely and evenly cut as in other portions of the cut grass swath. When second deflector  50  was added, the Applicants found that this streak in the grass substantially disappeared. The Applicants believe that this advantageous result is due to the upwardly sloped side surfaces  52  of second deflector  50  redirecting the two converging air flows and clipping streams enough that any deleterious effect on the cut grass swath is mitigated. In addition, second deflector  50  is thought to also cause the clippings generated by the center blade  32   c  and the counter-rotating side blade  32   s2  to fall out in a more even fashion across the width of rear discharge opening  24  behind these two blades. The shape and size of the sloped side surfaces  52  of second deflector  50  assists to redirect the air flows and clipping streams upward and toward the rear of the deck as opposed to what would have happened with side surfaces having substantially vertical configurations. 
     Deck  2  as described above improves the performance of deck  2  by improving the distribution of the grass clippings through rear discharge opening  24  while maintaining or improving the quality of cut over that achievable by prior art mowers. This would be true even if all cutting blades  32  used in deck  2  were of the same type, i.e. all higher lift blades. However, an additional incremental improvement is believed to be achieved by having the unidirectional blades  32   c  and  32   s1  be higher lift blades and the counter-rotating blade  32   s2  be a lower lift blade. While this physical difference in the blades is not strictly necessary and could be dispensed with, it is preferred to provide a rear discharge deck with the best possible performance. 
     Referring to  FIG. 7 , those portions of rear discharge opening  24  in back of side sections  26   s  of top wall rear portion  8  could be protected by trailing rear shields  70 . This would help prevent any debris or foreign objects from being thrown to the sides of deck  2 . In addition, a rearwardly extending shield, chute or tunnel (not shown) could be attached to the rear of deck  2  generally in back of center section  26   c  to help direct clippings rearwardly. 
     Various modifications of this invention will be apparent to those skilled in the art. For example, the downwardly inclined rear portion of top wall  4  could be replaced by a top wall  4  which is substantially horizontal over its entire extent. The downwardly and rearwardly inclined ramps would then be constructed of a separate fixed or removable ramp structure that is attached to the underside of top wall  4  of deck  2  over the portions previously occupied by the center and side sections  26   c  and  26   s  of top wall rear portion  8 . Moreover, the use of second deflector  50  between two counter-rotating blades  32  could be expected to improve the quality of cut and decrease streaking in the grass regardless of the type of deck as long as such deck has two adjacent counter-rotating blades in which the air flows are directed towards one another. Accordingly, the scope of this invention is to be limited only by the appended claims.