Abstract:
A vortex reducing mower blade for use with a rotary lawn mower having a motor and a depending drive shaft has a cutting edge on each leading edge thereof, an airlift on each trailing edge thereof, and outboard ends extending between the terminations of the leading and trailing edges. The outboard ends generally meet with the trailing edges at respective trailing corner- or tip-regions. Each outboard end has margins formed as a boundary-layer fence that is angled either upwardly or downwardly relative to a given relative up direction which is parallel to the central axis of the depending drive shaft. These boundary-layer fences reduce the production and/or strength of vortices in the wake of the trailing corner- or tip-regions of the blade. Each boundary-layer fence may be angled either upwardly or downwardly at generally a right angle. To produce a blade this way, generally the blade might be produced from flat steel stock including that each boundary-layer fence is formed as separate weldment from comparable flat steel stock for attaching in position by means of welding. Alternatively, each boundary-layer fence may be angled either upwardly or downwardly in generally a curving sweep. Producing a blade this way can be accomplished by producing the blade as a unit from a single stock piece of flat steel including that the boundary-layer fences are configured therein by means of a brake, stamping or press-forming operation.

Description:
CROSS-REFERENCE TO PROVISIONAL APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application No. 60/098,041, filed Aug. 27, 1999. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention generally relates to a vortex reducing mower blade and, more particularly, to a mower blade arranged in accordance inventive structures for managing and/or reducing the production and/or strength of vortices in the wake of the trailing corners of the blade tips. 
     It is an object of the invention to provide a rotary mower blade with vortex reducing structures to reduce the production and/or strength of vortices in the wake of the trailing corners of the blade. 
     It is an alternate object of the invention that the above vortex reducing mower blade reduce the production and/or strength of vortices in the wake of the trailing corners of the blade such that the vortices do not interfere with or decrease the suction (or lift) effect created by the airlifts in the trailing edges of the blade. 
     It is an additional object of the invention that the foregoing vortex reducing mower blade provide a more even trim of grass rather than an uneven trim seen when vortex production and or strength is too great. 
     It is a further object of the invention that the foregoing vortex reducing mower blade allow slower speed of operation to get the same suction power as given by a conventional blade not having vortex reducing structures operated at a higher speed. 
     These and other aspects and objects are provided according to the invention in a vortex reducing mower blade for use with a rotary lawn mower having a motor and a depending drive shaft has a cutting edge on each leading edge thereof, an airlift on each trailing edge thereof, and outboard ends extending between the terminations of the leading and trailing edges. The outboard ends generally meet with the trailing edges at respective trailing corner- or tip-regions. Each outboard end has margins formed as a boundary-layer fence that is angled either upwardly or downwardly relative to a given relative up direction which is parallel to the central axis of the depending drive shaft. These boundary-layer fences reduce the production and/or strength of vortices in the wake of the trailing corner- or tip-regions of the blade. Each boundary-layer fence may be angled either upwardly or downwardly at generally a right angle. To produce a blade this way, generally the blade might be produced from flat steel stock including that each boundary-layer fence is formed as separate weldment from comparable flat steel stock for attaching in position by means of welding. Alternatively, each boundary-layer fence may be angled either upwardly or downwardly in generally a curving sweep. Producing a blade this way can be accomplished by producing the blade as a unit from a single stock piece of flat steel including that the boundary-layer fences are configured therein by means of a brake, stamping or press-forming operation. 
     Another way of reckoning the vortex reducing mower blade includes the following. It comprises an elongated mower blade extending span-wise between spaced outboard ends. A central mounting portion allows mounting to a depending spindle. There are leading cutting portions proximate the outboard ends of the blade which are formed with respective leading cutting edges for rotating through a common cutting plane. There are also trailing lift portions respectively located behind the leading cutting portions and inclined upwardly from the cutting plane to terminate in trailing edges. 
     Wherein the location where each pair of trailing edges and outboard ends meet generally happens to define a respective trailing corner- or tip-region. Proximate each outboard end the blade further includes a chord-wise extending boundary-layer fence. Each boundary-layer fence is angled either upwardly or downwardly and as previously mentioned, acts to reduce the production and/or strength of vortices in the wake of the trailing corner- or tip-regions of the blade. 
     Generally speaking, absent the vortex reducing structures, the mower blade is conventional in at least some of the following respects. It is a rotary mower blade adapted for rotation about an upright axis. It extends span-wise between spaced end portions that terminate in outboard edges. Each end portion extends chord-wise between a leading flat portion sharpened to define a cutting edge and a trailing lift portion joined to and angled upwardly in trailing relationship to the leading flat portion and terminating in a trailing edge. The inventive improvement of said vortex reducing mower blade relates to a boundary-layer fence proximate to or forming a margin of the outboard edge of each lift portion. Each boundary-layer fence is angled either upwardly or downwardly as for reducing the production and/or strength of vortices in the wake of the trailing corner- or tip-regions of the blade. 
     It is an inventive aspect that each boundary-layer fence may be angled downwardly and given the shape of such a wedge as defined between an upper border common with the respective upwardly-angled lift portion and a lower border defined by an imaginary trailing continuation of the outboard edge of the respective leading flat portion. Each boundary-layer fence may be angled upwardly or downwardly in either a sharp right angle or else a curving sweep. If angled in a curving sweep, then each boundary-layer fence may be angled in the curving sweep such that the termination of which is generally oriented straight up or down as applicable. 
     Preferably but without excluding any other configuration, the trailing edges extend generally straight and generally parallel to a span-wise-extending plane containing the upright axis. Likewise, preferably but without excluding any other configuration, the outboard edges are generally contained in a chord-wise-extending plane that is parallel to the upright axis such that the trailing corner- or tip-regions are generally right-angled corners. 
     Optionally the vortex reducing mower blade may further comprise one or more span-wise spaced, chord-wise elongated vortilons distributed across either the upper or lower surfaces of the end portions. 
     Additional aspects and objects of the invention will be apparent in connection with the discussion further below of preferred embodiments and examples. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     There are shown in the drawings certain exemplary embodiments of the invention as presently preferred. It should be understood that the invention is not limited to the embodiments disclosed as examples, and is capable of variation within the scope of the appended claims. In the drawings, 
     FIG. 1 is a perspective view of a vortex reducing mower blade in accordance with the invention; 
     FIG. 2 is an enlarged scale detail from FIG. 1 of one of outboard ends of the mower blade (the other outboard end being a mirror opposite thereof); 
     FIG. 3 is an end elevational view of the outboard end of FIGS. 1 or  2 ; 
     FIG. 4 is an end elevational view comparable to FIG. 3 except showing the further provision of an upper boundary layer fence; 
     FIG. 5 is an end elevational view likewise comparable to FIG. 3 except showing the further provision of a vortilon; 
     FIG. 6 is a perspective view comparable to FIG. 2 except showing an alternate version of the boundary-layer fence configuration on the outboard end of the mower blade, and with portions broken away than in FIG. 2; and, 
     FIG. 7 is a perspective view comparable to FIG. 6 except showing another version of the boundary-layer fence configuration on the outboard end of the mower blade. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a perspective view of a vortex reducing mower blade  20  in accordance with the invention. The inventive mower blade  20  as it is shown in various example embodiments by the drawings herein, is arranged with alternative structures  50 ,  60  (eg., FIG. 4) and/or  70  (eg., FIG. 5) and so on, for managing and/or reducing the production and/or strength of trailing vortices, as will be more particularly described below. This provides highly desirable advantages for users of mower blades, as also will be more particularly described below. 
     The prospective use environment for the inventive mower blade  20  foreseeably includes, to date, the conventional use environments of prior art mower blades (not shown), ranging from without limitation a rather simple walking mower having a single-blade deck, to high-end riding mowers having multi-blade decks (neither shown). The operative use environment can include grass-cutting situations in which typically the mower deck has a chute for discharge of the clippings (and sometimes to an optional grass catcher), as well as include other situations in which the mower deck has no chute or the chute is blocked off as is sometimes desirable for mulching situations (none of this is shown). 
     The mower blade  20  in accordance with the invention is preferably formed from standard blank stock. Typically, standard blank stock is provided in the form of flat steel having a uniform thickness as well as a uniform width between opposite edges  22  and  24 , and which is cut to measure between opposite ends  28 . The blank stock is formed during fabrication to give the resultant blade  20  a central portion  32  flanked by opposite formed portions  34 . The central portion  32  is formed with the mounting formations for allowing the blade  20  to mount on a depending spindle (eg., drive shaft of the motor thereof) of a given rotary mower. One example mounting arrangement as shown by the drawings has the central portion  32  bored through with an enlarged center hole  36  and a pair of flanking mounting holes  38  for attaching the blade  20  to a spindle-mounting adapter (not shown) as is known in the art. The blade  20  is driven by the powerplant(s) of the particular mower it is mounted to as is also known in the art (and also not shown). 
     The blade  20  as shown in the drawings is arranged for revolving clockwise. However, the blade  20  is shown this way merely for convenience in the drawings and hence this is not limiting because the blade  20  can be formed in a mirror opposite arrangement as is commonly done to render it suitable for operating in the counterclockwise direction. 
     Each formed portion  34  extends between a leading edge  22 L or  24 L and a generally parallel trailing edge  22 T or  24 T, both which terminate in corners with the respective outboard end  28 . The leading edge  22 L/ 24 L is ground with a beveled cutting edge, usually at about a 30° angle or so. The formed portions  34  are bent along a fold line  40  that lies between and extends generally parallel with the leading and trailing edges  22 L/ 24 L and/or  22 T/ 24 T. The bend at the fold line  40  produces in the blade  20  both a flat panel  42  that originates behind the leading edge  22 L/ 24 L and a ramp panel  44  that terminates in the trailing edge  22 T/ 24 T. This ramp panel  44  is more commonly termed an “airlift.” 
     The airlift  44  (which is sometimes referred to as the “camber”) acts as a fan to create a suction or a least reduce or evacuate the air pressure. Suction is useful for straightening bent or reclining grass-blades to a more upright erect position to gain as much of an even trim of the grass-blades as possible (not illustrated). Suction is also useful for swirling around the clippings for mulching purposes and/or for discharging the clippings out an appropriate chute for them. 
     In FIG. 2, the corner  48  between each trailing edge  22 T or  24 T and the respective outboard end  28  forms what is termed here the “trailing tip.” 
     A shortcoming with prior art mower blades involves vortex production in the wake of such trailing tips  48  of the airlifts  44 . In general, a vortex is a swirling current created by differences in air pressure and velocity between the high pressure (low velocity) region above the airlift  44  and the low pressure (high velocity) region below. Physically, this corresponds to high pressure airflow from above the airlift  44  rolling down around the outboard end  28  to join the low pressure airflow below the airlift  44 , causing a downwardly and inwardly swirling vortex shedding off the trailing tip (these flows and/or currents are not illustrated). 
     Strong vortices are problematic because they swirl the grass-blades around in spiral reclining positions or even blow them down flat by virtue of strong down eddies. Grass-blades being swirled around or blown flat is counter-productive to the useful work of the airlift  44 :—ie., in suctioning up the grass-blades into an upright erect position. 
     Vortices are detrimental to the overall trim of the grass because the trim height is correspondingly undesirably uneven. The problem of the vortices is aggravated by speeding up any of the prior art mower blades (but this condition is not as strictly applicable to the inventive blade  20 , as will be described more particularly below). Whereas a higher speed does induce a greater suctioning force, it correspondingly produces stronger vortices from the prior art blades such that the gains in suctioning force are not just offset but worsened by such stronger vortices. 
     Moreover, the problem of vortices is compounded in mowers having multi-blade decks. Where the swaths of two blades overlap, they create interfering vortices. The sum of the detrimental effects left by the trail of the interfering vortices is greater than the vortex trail left by one blade alone. Users of multi-blade mowers—especially with counter-rotating blades—are familiar with stripes of long grass they leave behind that corresponds to where the swaths of adjacent blades overlap. 
     What is needed is an improvement in prior art mower blades to provide management and/or reduction in the production of and/or strength of such vortices. Therefore these and other aspects and objects are provided according to the invention in a mower blade  20  in accordance with the invention, of which one version of vortex management and/or reduction for mower blades is shown by FIGS. 1 through 3. 
     The outboard ends  28  are provided with an inventive, wedge-shaped boundary-layer fence  50 . As best shown by FIG. 3, the wedge-shaped boundary-layer fence  50  fills the wedge-shaped space defined by the bent-up airlift panel  44  and an imaginary continuation of the flat panel  42 . With the fence  50  arranged as shown, a portion of the high pressure flow from above the airlift  44  rolls around the fence  50  and deflects the low pressure flow below the airlift  44  in opposition to the normal rotation of a shedding vortex, and thereby weakens the resultant vortex. The physical phenomenon of this flow interaction is more fully given by reference literature elsewhere, including without limitation, what is disclosed by U.S. Pat. No. 4,108,43—Finch, the disclosure of which is incorporated herein by this reference to it. 
     Trials with the fence arrangement  50  depicted by FIGS. 1 through 3, have shown that weakening the vortices provides numerous advantages. Apparently, the vortices are weakened such that they depress much less grass in counter-action to the suction of the airlift  44 . Hence the apparent “lift” of the grass is better. Perhaps there is less “loss” to what is physically available for lift and so there is an apparent “gain” in the lift or suction of the grass. Regardless, observed improvements and advantages gained by the inventive mower blade  20  provided with the boundary-layer fence  50  as shown, include without limitation a few of the following. 
     By one easy measure, a user gains—as plainly evident by even merely casual observation—a much more cleaner cut for the grass. Simply put, the trim height is plainly more even. 
     Also, the inventive blade  20  works better on wet grass. In wet grass, individual grass-blades are already partially depressed by the weight of the wetness, and that also makes them heavier to lift and in some cases they are stuck together in clumps. Gains in lift or suctioning mean that the inventive mower blade  20  handles wet grass better than its prior art counterparts. 
     For another thing, the speed of the blade  20  can be slowed for safer operation. That is, the inventive blade  20  provides as much or comparable lift as its prior art counterparts when revolved at relatively slower speeds. 
     Still further, speeding up the revolving of the blade  20  provides gains in lift or suctioning whereas in prior art blades, speeding them up only creates a worsened situation with vortices. 
     Additionally, gains in lift allow a user to let the height of the blade  20  remain relatively higher for suctioning up heavy matter such as leaves of the like. By way of background, a user of a prior art blade might drop his or her normal blade height for grass (perhaps corresponding to 3½ or 4 inches or so, or 9-10 cm), down by about half (eg., to about 2 inches or 5 cm) for suctioning up leaves in a mulching operation. Whereas a lowering a blade does provide gains in lift, a lower blade is more generally undesirable because it exposes the blade to more risk of damage on rocks or tree-root knees and the like. 
     In accordance with the invention, gains in lift provided by the inventive blade  20  allow a user to keep the blade height at his or her normal height even for leaf-mulching operations and the like. 
     FIGS. 4 and 5 show alternative examples  60  and/or  70  for the management and/or reduction in the production and/or strength of vortices in mower blades, whether used in combination or not with the wedge-shaped fence  50 . 
     FIG. 4 shows a low, boundary-layer fence  60  established on the upper surface of the blade  20 , extending substantially across the width of both the flat panel  42  and the airlift panel  44 . This upper fence  60  as shown is located flush along the outboard edge  28 . However, it might be preferred to deploy a set of such an upper fence  60  as distributed along the span of the leading edges  22 L or  24  L from a given inboard extreme (not shown) to an outboard terminus at the very outboard edge  28  (again, this is not shown). This upper fence  60  is believed to act to contain some fractional amount of the high pressure flow that potentially would roll around the outboard end  28  of the blade  20 , and in consequence act to reduce vortex production and strength. In FIG. 4, the upper fence  60  is intentionally low with respect to the bevel of the cutting edge  22 L. That way, the upper fence  60  does not interfere with grinding of the bevel  22 L in re-sharpening operations for a dull blade  20 . 
     FIG. 5 shows a special case of a boundary-layer fence  70 , known as a “vortilon.” Vortilons on aircraft typically have noses that jut ahead of the leading edge of the wing they are mounted on (no “wing” is shown by the drawings), as well as typically are established on the high pressure side of an aircraft wing. Hence, on aircraft wings, vortilons are typically suspended beneath the wing but here, the vortilon  70  is positioned on the upper surface of the blade  20  at the outboard end  28 . Also, a vortilon  70  such as this one is typically used in a set, the members of which are distributed along the span of the respective airlift  44  or aircraft wing to which they are attached (eg., as commonly seen on Long EZ aircraft which were originally designed by the Rutan brothers, Burt and Dick). Likewise it is preferred if this vortilon structure  70  here is used in a set that is distributed across the span of the leading edge  22 L or  24 L at spaced inboard-to-outboard locations (not shown). 
     Referring back to FIG. 2, one way of configuring the mower blade  20  with the vortex-reducing fence  50  is the following. The fence  50  is pre-cut from a separate stock of flat steel material that is comparable to the flat steep material forming the main body of the mower blade  20  (this is not shown). The pre-cut piece that will become the fence  50  is cut generally in the shape of a wedge. The shape of this wedge is described above. Briefly, that is, as best shown by FIG. 3, the shape of the wedge corresponds to the wedge-shaped space defined by the bent-up airlift panel  44  and an imaginary continuation of the flat panel  42 . Given that shape, the pre-cut wedge is then fitted in the above-described space for it and welded in place. Grinding off excess weld material blends the contours of the mower blade  20  and fence  50  to give the results which are best shown by FIG.  2 . 
     FIG. 6 shows an alternate version of the FIG. 2 style vortex-reducing fence  50 , wherein FIG. 6 shows a fence  50 ′ which is produced by a stamping operation. More particularly, that is, the FIG. 6 fence  50 ′ is formed as a unit from the same stock piece that constitutes the main body of the mower blade  20 ′. In other words, during a single braking or stamping operation, the mower blade  20 ′ is formed from a flat stock piece into the formed mower blade  20 ′ all at once. This includes not only the formed portion  34  and airlift  44 ′ but also the fence  50 ′ as well. Comparing FIGS. 2 and 6 shows that the FIG. 6 fence  50 ′ has rounded fold lines whereas the FIG. 2 fence  50  defines a sharp right-angle crease that is the product of welding and grinding. 
     FIG. 7 shows another version of the FIG. 6 style vortex-reducing fence  50 ′. wherein FIG. 7 shows a fence  50 ″ likewise produced by a stamping operation. Comparing FIGS. 6 and 7 shows that the FIG. 7 fence  50 ″ is folded on an angle that is coming back inboard slightly rather than as in FIG. 6, being fairly close to parallel with a chord-wise axis. This is explained better by more difficult language as follows. The outboard edge  28  of the leading flat portion  42  generally extends along an axis C. This axis C extends in the chord-wise direction relative to the span of the blade  20 ″. To understand these relative axes, it is easiest to reckon the blade  20 ″ as mounted to an upright spindle of a rotary mower such that the spindle on flat ground is more or less vertical and the plane which the cutting edges  22 L sweep through is generally horizontal. 
     Given the configuration of this blade  20 ″, its trailing edge  24 T generally extends along an axis which is parallel to a span-wise axis or spoke extending through the spindle (not shown) and which is horizontal. Again, the trailing edge  24 T extends along a horizontal axis indicated by reference letter H that is parallel to a span-wise axis or plane (not indicated) containing the vertical spindle the blade  20 ″ mounts to. That portion of the outboard edge  28  that extends along the leading flat portion  42 , extends along a true, horizontal chord-wise axis C. The trailing corner  48  of this blade is defined by where the trailing edge  24 T meets the boundary layer fence  50 ″. If a vertical axis V is dropped from this corner  48  to the horizontal plane containing horizontal chord-wise axis C, and then the axis F is drawn in, it being the projection in this horizontal plane of the fold line for downwardly-angled fence  50 ″. Therefore, axis F is the projection down of the fold line angle of boundary-layer fence  50 ″ in the horizontal plane that not only contains horizontal chord-wise axis C but also the leading flat portion  42 . 
     Given the foregoing, FIG. 7 shows that the boundary layer fence can be bent down from the web of the airlift  44  but at slightly cocked angle not true to the vertical plane containing the outboard edge  28 . The drawing shows this slightly cocked angle being the divergence between axes C and F which are commonly contained in a horizontal plane containing leading flat span  42 . It is preferred that the FIG. 7 version of the invention be limited to cases where the boundary-fence  50 ″ is angled downwardly and not upwardly relative to the web of the airlift  44 . This is especially more preferred in cases where the divergence between axes C and F becomes progressively larger. 
     The purpose behind the FIGS. 6 and 7 embodiments is particularly for accommodating blades stamped from thick gauge plate, a thickness being in mind of ¼-inch (6 mm) or so (and not excluding thicker or thinner materials). The common steel that blades are presently made of (and known to the inventor) start not to bend easily along sharp fold lines for right angles when the material gets about ¼-inch (6 mm). Materials of other alloys experience bending this way with difficulty at greater or lesser thicknesses, but this is not exactly known. In fact, FIG. 7 shows an inventive way of accommodates the truly least pliant of materials for adaptation in accordance with the invention. 
     The invention having been disclosed in connection with the foregoing variations and examples, additional variations will now be apparent to persons skilled in the art. The invention is not intended to be limited to the variations specifically mentioned, and accordingly reference should be made to the appended claims rather than the foregoing discussion of preferred examples, to assess the scope of the invention in which exclusive rights are claimed.