IE43172B1 - Cutter disc assembly for rotary lawn mower - Google Patents

Abstract

1526519 Lawn mowers ROPER CORP 25 Aug 1976 [8 Sept 1975 18 Aug 1976] 35376/76 Heading A1F A cutter disc assembly for a rotary lawn mower having a vertical shaft comprises a disc 20, preferably made of plastics, having a central portion 21, a peripheral portion 23, a number of radially aligned resilient plastics cutter pins 33 held in cantilever mountings adjacent their heads 35 to extend radially across and outwardly of the peripheral portion 23; the pins being of tapered construction and/or being provided with curved support means 41 to smoothly distribute curvature in the pin when deflected by an obstruction in use; the pins being capable of bending to a position where they are wholly protected by the peripheral portion, Fig. 11 (not shown). The pin may be tapered and may be inclined so that its tip 38 is below the level of the cutter disc. Vents (61, 63) Fig. 4a (not shown) in the central portion cause an updraft of air. In alternative embodiments the pins 130 are held in flared grooves 137-139 in the underside of the peripheral portion 123, Fig. 12, and the grooves have a ceiling 147 connected by a rib 157 to the centre of the disc, the ribs being provided for reinforcement and to cause a turbulent air current. The ceilings hold the pins in their inclined positions and to dampenout oscillation; the curved walls 142, 143 of the grooves serve to distribute curvature in the pins both on bending backwards after striking an obstruction and on subsequent forward bending, Fig. 16. The pins, which may have non-circular cross-sections, e.g. cruciform Fig. 26, may be located by passing through two depending annular walls 122', 122", Fig. 14, or may be held in two saddles 122', 122" Fig. 20. A floor below the pins may also be provided, Figs. 32-34 (not shown).

Description

FA'!ENT APPLICATION BY (71) ROPER CORPORATIONA DELAWARE CORPORATION HAVING A PRINCIPAL PLACE OF BUSINESS AT 1905 WEST COURT STREET, KANKAKEE, ILLINOIS 60901, UNITED STATES OF AMERICA.

Prtci I2d 43173 Many designs of mower blades have been devised, made of plastics-or the like, for the purpose of overcoming the hazards of the conventional steel rotary mower blade. Notwithstanding the fact that the cutter elements are made of plastics, the prior structures are capable of flinging missiles and capable of inflicting serious injury by direct impact upon the foot of the operator or upon the hand of a curious child. Thus there has been recent concentration upon weed cutters θ employing a thin, relatively limp whirling filament of plastics, namely nylon. It will suffice to say that filamentary cutters are ineffective in a thick stand of grass or against heavy or fibrous weed stalks, and are subject to constant breakage.

It is accordingly an object of the present invention to provide a cutter disc assembly for a rotary mower which reduces the hazards of steel blade cutter designs, which reduces the potential of serious injury either by missile or direct impact, and which is, at the same time, highly effective in. cutting grass or weeds. -3Advantageously, a cutter disc is employed with sockets for mounting cutter elements in the form of pins of plastics material having relatively stiff shank portions terminating in long flexible stiffly resilient tip portions. The shank portion of each pin is anchored inwardly of the edge of the disc so that only the flexible stiffly resilient tip portion extends beyond the disc for severing grasp and weeds with whiplash action but which, by reason of low mass, yields harmlessly when striking any more weighty object.

The disc itself, by reason of its generally circular shape, is incapable of striking a blow. Consequently, the safety of the unit far exceeds that of conventional constructions .

In an embodiment of the present invention there is provided a cutter disc assembly which is, in addition, self protecting and in which the cutter elements, instead of being exposed and vulnerable, are shielded and fully protected against damage or breaking off, even under the most severe conditions, as, for example, encountered in the mowing of a wild area or a vacant lot strewn with heavy debris. Advantageously, there is provided a self-protecting cutter disc assembly in which the tip portions of the pins, upon striking constructions are free to bend back toward, or into, the protection of the disc upon which they are mounted, with the edge of the disc limiting the bending to safe degree.

In a preferred embodiment of the invention there is provided a cutter disc assembly having long flexible stiffly resilient plastics pins which are mounted cantilever fashion inwardly of the disc periphery, and, in which assembly each pin has means for insuring smooth bending of the pin to avoid concentration of stress. As a - 4 result, the service life of a pin is greatly extended, and the need for constant renewal, as in filamentary type cutters, is avoided.

It is an important advantage of the invention that the cutter disc assembly is not only highly efficient and self-protecting, but also, by reason of the resilient yielding of the light, flexible stiffly resilient cutter pins upon striking a pebble, piece of glass or similar foreign object, makes it substantially impossible for the object to be ejected, as a missile, from the mower housing. If ejection should, in rare circumstances, occur, the speed of ejection is in any event reduced to a level considerably less than with conventional blades.

In another preferred embodiment of the invention, there is provided a cutter assembly in which the shank portion of the pin is nested in a downwardly facing groove having a curved outwardly flaring rear wall against which the pin is bent upon striking an obstruction as well as a curved outwardly flaring front wall upon which the pin bends upon rebound, the effect in both cases being to distribute the bending to avoid concentrated stress which would result in eventual breakage. Advantageously, there is provided a disc construction in which the groove has a ceiling which is utilized to hold the tip portion of the pin in a downwardly-angled cutting position, with the engagement of the pin and ceiling serving to dampen pin movement.

Embodiments of the invention are hereinafter described, by way of example with reference to the accompanying drawings, in which:Figure 1 is a perspective view of a rotary mower including the present invention with a portion of the 43173, - 5 housing broken away to reveal the cutter disc assembly.

Figure 2 is a perspective view of the underside of the mower of Figure 1.

Figure 3 is a perspective top view of the cutter 5 disc assembly.

Figure 4 is a top view of the cutter disc assembly looking along the line 4-4 in Figure 5.

Figure 4a is a fragmentary view of a modification of the central portion of the cutter disc assembly of Fig10 ure 4.

Figure 5 is a section taken along line 5-5 in Figure 4.

Figure 6 is an enlargement of a portion of Figure .

Figure 7 is an enlarged fragmentary underside view looking along line 7-7 in Figure 6.

Figure 8 is an enlarged fragmentary top view looking along line 8-8 in Figure 6 and showing the bending back of a cutter pin into the protection of the disc upon striking of a weighty obstruction.

Figure 9 is a partial section similar to Figure 6 but showing a modified structure.

Figures 10 and 11 correspond to Figures 6 and 8 but show substitution of a straight-sided pin as a modification of - 6 4 317 2 the invention.

Figure 12 is a perspective view of the underside of a mower employing a modified form of cutting assembly.

Figure 13 shows the top side of a cutter disc of 5 Figure 12.

Figure 14 is a cross section of the cutter disc taken along the line 14-14 of Figure 13 with a cutter pin in place.

Figure 15 is a fragmentary elevation of the cutter 10 disc looking along line 15-15 in Figure 13.

Figure 16 is a fragment showing the underside of the disc at one of the pin positions with the pin shown both in its extended and bent 'conditions.

Figure 17 is a fragmentary elevation looking along 1.5 the line 17-17 in Figure 13 showing the overhanging ledge providing protection for a pin in bent condition.

Figure 18 is a view similar to Figure 16 but showing a modified form of the invention.

Figure 19 is a fragmentary top view of the disc 0 taken at one of the groove positions.

Figure 20 is a radial section looking along line 20-20 in Figure 19.

Figures 21-24 are a series of parallel, transradial sections taken on corresponding section lines in Figure 19. 43l7:i - 7 Figure 25 shows the underside of the portion of the disc shown in Figure 19.

Figure 26 shows a preferred form of pin employed with the structure shown in Figures 19-25, Figure 27 is an end view of the pin of Figure 26.

Figure 28 is a sectional view similar to Figure 20 and showing the cooperating dies employed to form the disc.

Figure 29 is a vertical section looking along line 29-29 in Figure 28.

Figure 30 is a view similar to Figure 25 and showing the protected area relationships.

Figure 31 is a fragmentary vertical section of a modified form of disc looking along line 31-31 in Figure 32.

Figure 32 is a fragmentary top view looking along the line 32-32 in Figure 31.

Figure 32a is a fragmentary section looking along line 32a-32a in Figure 32.

Figure 33 is a fragmentary perspective of a further 20 modification of the invention.

Figure 34 is a vertical section looking along line 34-34 in Figure 33.

Figure 35 is a vertical fragmentary section Of a still further modification of disc looking along line 35-35 - 8 in Figure 36.

Figure 36 is a fragmentary top view looking along the line 36-36 in Figure 35.

While the invention will be described primarily in connection with a number of preferred embodiments, it will be understood that we do not intend to be limited to any particular embodiments shown but intend, on the contrary, to cover the various alternative and equivalent constructions included within the scope of the appended claims.

Turning to Figures 1 and 2, there is shown a type of rotary mower in common use and to which the present invention is applicable. It includes a frame 11 in the form of a shallow inverted enclosure having an encircling sidewall 12, a set of wheels 13, a handle 14 to provide guidance, and an engine 15 which may, alternatively, be an electric motor, having a vertical drive shaft 16 which is conventionally tapped for receiving a clamping screw 17.

A discharge chute 18 projects from one side of the housing to dispose of the clippings.

Secured to the drive shaft in horizontal position is a cutter disc 20 which carries the cutting elements.

Such a disc, which is preferably molded of a durable and resiliently deformable plastic, has a circular central portion 21 (Figures 3-5), a shallow wall or offset portion 22 and an annular outer portion 23. Secured axially in the center portion 21, to provide durability, is a metallic hub 25 which may, for example, be made of aluminium alloy. The hub, in addition to a central opening 26, has a set Of peripheral openings 27 registering with projections 28 formed in the molded piece for locking the hub in place. - 9 Evenly spaced, radially extending openings, or sockets,31,32 are formed in the shallow wall 22 for receiving cutter pins 33,34, respectively.

Referring to a typical cutter pin 33, as shown in Figure 5, it includes a head 35, a shank portion 36 and a long tapering relatively flexible tip portion 37 merging with the shank portion and terminating in an outer tip 38. The pin 33 is made of a tough resilient abrasion-resistant resilient plastics material and has a cross-section such that the flexible tip portion 37 is stiffly resilient. The inner end of the shank portion 36 of the pin is dimensioned to fit snugly, cantilever fashion, in the radial opening 31. The opening 31 serves as a mounting means holding the pin in a position in which it is spaced upwardly from the undersurface of the outer portion of the disc. More specifically, the opening 31 is formed in the lower portion of the shallow wall or offset 22 so that the annular outer portion 23 of the disc closely underlies and protects the relatively stiff shank portion 36 of the pin while the tip portion 37 of the pin projects beyond the periphery 24 of the disc into cutting engagement with the grass G. Because the shank portion 36 of the pin 33 is spaced well inwardly of the periphery 24 of the disc, approximately one-half of the length of the pin being included within the disc perimeter, the shank portion of the pin is completely shielded against radially encountered obstructions, the tip portion 37 of the pin being free to bend increasingly into the protection afforded by the disc upon striking of an obstruction. At the same time, the shank portion of the pin, by reason of its position above the underside of the disc,is shielded against obstructions which engage the disc axially. While about one-half of the length of the pin extends beyond the perimeter of the disc, preferably the length of the pin is at least one and one-half times the radial width of the outer portion of the disc utilizing the pin. In any event the pin should project from the disc at least a half-inch and preferably at least two inches. - 10 There are located adjacent the radial openings 31, 32, upstanding radial backstops 41,42, respectively securely joined to the disc and having a retreating curvature for engaging and providing lengthwise-distributed support for the associated pin during its backward bend and also serving as air vanes. Thus, taking the backstop 41 by way of example (Figure 6), it has a lower edge 43 which is integrally joined with respect to the peripheral portion 23 of the disc and an inner edge 44 which is integrally joined with respect to the shallow wall 22 to provide radial reinforcement.

In carrying out the invention, the backstop is shaped to present a curved face 45 (Figures 7 and 8) lying adjacent the pin 33 and which terminates in an end 46 which is spaced inwardly from the periphery 24 by a clearance distance shown at D in Figure 8.

Thus when an obstruction is encountered, for example, in the form of a rock or pebble P, its mass applies reaction force against the pin 33, causing the pin to be bent back in the most extreme case to the curved position shown dot-dash in Figure 8. Only the tip portion 37 of the pin 33 is accessible to the rock or pebble, and since it is highly resilient, and of low mass, the backward bending takes place to relieve the force before the force, indicated at F, can increase to a degree which might create a dangerous missile.

For the purpose of promoting radial air flow so that the clippings are blown clear of the disc, sector shaped through-openings 61 (Figure 4a) may be formed in the central portion 21 of the disc defined by radially extending spokes 62. - 11 The radially extending surfaces of the openings may be beveled as shown at 63 so that air is forced through the center portion of the disc by scooping action.

While the function has been described in connection with backstop 41, it will be understood that backstop 42, which is diametrically opposite, acts in the same way.

In the preferred form of the invention two cutter pins 33, are used. However, the invention is not limited to use of two cutter pins and either a single cutter pin may be used or additional cutter pins may be spaced about the periphery of the disc, for example, cutter pins 33a, 34a with their associated backstops 41a, 42a (Figure 4).

As one of the features of the present construction, the annular outer portion 23 of the disc, and the openings (for example opening 31) which register the pins, are not oriented perfectly horizontally but are, instead, angled downwardly at a shallow angle. The bottom surface of the disc may be angled downwardly by an angle a (Figure 6) of at least 1 degree but preferably 2 degrees or more to form a shallow conical surface, while the opening 31, and hence the pin which it contains, is angled downwardly by a slightly greater angle β which may be on the order of 2 to 8 degrees, and preferably 4 to 5 degrees, the difference between α and β preferably being no greater than 3 degrees. As a result, the outer tips 38 of the pins lie at a lower level than the periphery 24 of the disc, to insure that cutting takes place at lower than disc level. Thus it is not necessary for the disc to drag or brush against the standing blades of grass in the cut condition. This, in turn, reduces the effort required to push the mower. - 12 It is a further feature of the present invention that the pins are angled with slight retreat, that is, opposite to the direction of rotation of the disc, by an angle γ with respect to the radius as shown in Figure 7, which angle is in the range of from 1° to 9° and preferably of the order of 6°.

It will be apparent in view of the above that the cutting pins are protected in at least two different ways. Because of the closely underlying annular portion 23 of the disc, any obstructions which may be encountered by the mower either radially or axially of the disc are prevented from having access to the shank portions of the pins which are relatively stiff and thus subject to breakage, if unprotected. Conversely any obstruction is limited to engagement by the light, stiffly resilient tip portion 37 of the pin which, bending backwardly about its backstop and into the radial confines of the disc, simply lets the object go by without developing a force capable of converting the object into a hazardous missile. To minimize transfer of momentum from the flexible cutting element, the weight of the projecting tip portion 37 should be kept low, for example, below about 2 grams.

While a pin made of durable plastics, inherently protected by the disclosed disc construction, may be expected to have a long life, it is one of the features of the present mower that any pin may be replaced, without special tools, in a few seconds time. The head 35 of the pin, protected in its recess 39, may simply be pushed inwardly for removal by grasping the outer end of the pin, without use of tools, or may be pried by any edge tool such as a screwdriver, toward the dotted position shown in Figure 6. Once the shank portion 36 has been loosened, the pin may be retracted radially inwardly by the fingertips, 43ί 72 - 13 and a new pin substituted.

Also in the preferred form of the invention, and to facilitate replacement of the pins when replacement becomes necessary, the outer, or peripheral, portion 23 of the disc is, as shown in the drawings and stated to be, at a lower level than the circular central portion 21. It is not essential , however, that these two portions 21 and 23 be at a different level and they may, indeed, be at the same level and form a radial continuation of one another.

There is also provided an axially offset portion at the junction between the central portion and outer portion providing a plurality of radially extending openings for registration of tapered pins, with the shanks of the pins being held, cantilever fashion adjacent the pin head, in a protected position extending just above the outer portion of the disc and with the pins being of tapered construction to secure smooth curvature and freedom from concentrated stress. Such a structure is shown in Figure 9 in which the same reference numerals as in Figure 6 have been used to designate similar parts with addition of subscript c. Such construction may be used without a backstop.

The embodiment shown in Figure 9 possesses the same general advantages as the earlier embodiment except that th pins are not quite so readily replaceable, requiring re ioval of the disc; such captivity may be considered as an advantage in some applications. The wall 22c is preferably annular.

One of the features of the embodiments of the invention described above, has been the fact that each pin is of tapered, configuration, providing a high degree of flexibility and low mass at the tip portion 37 but with - 14 a shank portion 36 of relatively larger diameter resulting in a natural cantilever bending curvature which increases in the direction from the shank portion to the outer tip 38. However, it is understood that the invention may be practiced, if desired, employing a cutter pin which is of substantially constant thickness, with a curved backstop to prevent concentration of bending stress. Such a parallel-sided pin is illustrated in Figures 10 and 11 which correspond to Figures 6,7 and 8 of the earlier embodi mentj similar reference numerals being employed with addition of subscript d. As in the earlier embodiments, the tip is protected by bending retreatingly toward, or into, the confines of the disc periphery, the main difference being that the section of the tip portion 33d adjacent the outer tip 38d of the pin tends to remain more straight than in the case of the tapered pin. One advantage of the parallel-sided pin is that the pins may be produced easily and cheaply by extrusion, with the head being formed, for anchoring purposes, by a separate terminal heading operation. A further advantage is that there is more material available for wear and abrasion at the tip, which may be desirable when using the mower for heavy weeds, brush and like, either with or without an increase in driving horsepower.

Turning to Figure 12, there is shown another embodi ment of the present invention. Secured to the drive shaft in a horizontal position is a cutter disc 120 which carries the cutting elements. Such disc has a circular central portion 121 (see also Figures 13 and 14), an axially offset or wall, portion 122, and a periphery portion 123 of relatively thin average cross section extending from a dropoff 124 and presenting an outer edge 125. Centered in the disc is a mounting hole 126 which may be optionally reinforced by a metal reinforcing disc either secured to or - 15 molded in the disc structure.

Evenly spaced openings 127, 128, 129 are provided in the wall portion 122 of the disc for receiving outwardly extending cutter pins 130. Each pin includes a head 131, a shank portion 132 and a stiffly resilient tip portion 133. terminating in an outer tip 134. The shank portion 132 is dimensioned to fit snugly, cantilever fashion, in a radial opening, for example, the opening 127.

The annular outer portion 123 is formed, on its 1° underside, with radially extending grooves in register with the respective openings for receiving the shank portions of the pins, each groove having a downwardly angled ceiling, a narrow neck portion, and a curved, outwardly flaring rear wall against which the pin bends as the projecting tip portion strikes an obstruction as well as a curved outwardly flaring front wall against which the pin may bend upon rebound, thereby to support the shank portion of the pin with the bending distributed along the length thereof for avoidance of concentrated stress.

Referring to Figtres 12-16, the grooves are indicated at 137, 138, 139 in respective alignment with the pin receiving openings 127,128, 129. Taking the groove 137 as representative, and referring to Figures 13,16, the groove has a relatively narrow neck 141 having a width d which just slightly exceeds the diameter on the shank portion 132 of a pin 130. The groove has a curved, outwardly flaring rear wall 142 which is of increasing curvature and which is tangentially flared into the periphery of the disc. The rear wall 142 serves as a support on backstop for the shank of the pin as the tip portion of the pin strikes an obstruction,for example, in the form of a rock or other - 16 weighty piece of debris, R (Figure 16), with the bending of the pin against the curved wall serving to distribute the bend smoothly in the pin so as to avoid the setting up of concentrated stress. The groove, in addition, has a front wall 143 adjacent the pin which is curved and outwardly flaring so that when the pin 130 is released, tending, because of its resilience, to rebound in the forward direction through an angle θ , the pin bends about the curved front wall 143 with the bending, again, being distributed along the length dimension of the pin for avoidance Of concentrated stress. The flaring curvature and the narrowness of the throat 141 produce a groove profile which, viewed vertically, is of trumpet shape. Since the curvature of the rear wall 142 causes it to merge smoothly into the periphery 125 of the disc, there is no abrupt discontinuity and the outer portion of the pin is supported, in bent condition, upon the periphery.

In this embodiment of the present invention, a substantially horizontal bridge is provided closely overlying the pin at the periphery of the disc, for the purpose of providing a ceiling surface for holding the pin in downwardly angled working position over its range of lateral motion. Thus each groove includes an inclined but substantially flat ceiling 144 which is oriented outwardly and downwardly at a shallow angle thereby to provide a superimposed guide surface for not only holding the pin to the work but also for damping the lateral movement of the pin. The angling of the ceiling from the horizontal, indicated at β in Figure 14, is preferably within the range of 2° to 8°.

The projection of the tip portion 133 of the pin below disc level tends to insure that the cut grass will not drag on the bottom surface of the disc. The ceiling 43178 - 17 144 of the groove, by its contact with the pin, overcomes the tendency of the pin to ride at a higher level, that is, to straighten out horizontally as a result of centrifugal force, tending to keep the tip portion of the pin at a desired cutting level in spite of variations in the centrifugal force. The ceiling is of such height h (Figure 14), i.e. the groove 137 has such axial depth, as to contain the shank portion 132 of the pin 130 and thus shield and protect it against abrasion from the underside of which occurs when the rapidly rotating disc is, during the course of mowing, brought against some sharp projection on the surface of the ground.

In this embodiment of the present invention the ceiling suriaces 144 of the respective grooves 137 , 138, 139 are formed by integral reinforcing bridges 147,148, 149. Taking the groove 137, and its bridge 147, as representative, it will be seen in Figure 15 that the bridge 147 is a region of the outer portion 123 of the disc where the disc has augmented thickness t. The region of augmented thickness extends peripherally over a length L which substantially overlaps the side walls of the groove, and extends radially from the dropoff 124 to the outer edge 125 of the disc. Each bridge thus serves to reinforce the disc to make it uniformly strong.

Referring to Figures 13, 14 and 15, vanes 157, 158, 159 extend from the central portion of the disc radially outwardly for joining at their outer ends to the trailing edges of the respective bridges. The vanes are of special upwardly-swept cross-section (Figure 15) so as to create upward movement of the air in the immediate vicinity of the pins. Where the disc has no through-openings the vanes tend to cause a partial vacuum above the disc which causes the grass to be agitated as it is being cut. The - 18 vanes not only create desired air flow as the disc rotates at high speed, but also insure that the disc is reinforced in multiple directions, the bridges providing peripheral reinforcement while the connected vanes provide radial reinforcement.

Lightness is enhanced by specially constructing the wall portion 122 of the disc. Preferably the wall portion 122 is relieved by forming therein a circular groove 160 to define two ribs 122', 122 (see Figure 14) which are concentric and radially spaced from one another over most of their length with aligned openings so that the shank portion 132 of the pin is gripped at longitudinally spaced regions to provide firm cantilevered support with a minimum of supporting structure.

However, to practice the invention it is not necessary for the wall 122 to be continuous or for there to be a single central recess for removal and replacement cf the pins. If desired, the wall portion 122, in which the pins are retained, may be discontinuous and the wall may be formed of separate segments 165 formed at one end of an individual radial recess 166 provided for each of the pins (see Figure 18).

Advantageously, there is provided, at the point where the rear wall 142 merges with the periphery 125 of the disc, a ledge 161 which overlies the tip portion 133 of the pin 130 as it is bent backwardly upon striking of an obstruction, the ledge merging at its forward end with the periphery of the disc to facilitate the disc's wiping by the obstruction. Referring particularly to Figures 13,16 and 17, it will be noted that the bridge 147, along its trailing edge, is extended radially outward to form an overhanging ledge 161 which projects beyond the periphery 125 by an amount indicated at r (Figure 13), which approximates the thickness of the pin at the point of exit. The bridge 147 is preferably smoothly flared with respect to the periphery of the disc at its leading edge indicated at 162 to insure that the obstruction is cammed away from the pin so that the pin is protected from radial abrasion. Since the amount of material which forms the periphery of the disc is substantially greater than the amount of material used in the tip portion of the pin, the disc is well able to absorb the impact and forces of abrasion while imparting to the pin a much longer life in the face of rough usage.

While the shank portions of the pins are protectively enclosed in downwardly facing grooves, it is found that grooves remain free of crushed grass and other debris which might affect the freedom of the pin to bend backwardly and forwardly under stress. The reason for such freedom is believed to be the fact that each pin, in the normal operation of the mower, constantly works back and forth and the grooves, being of flaring shape, are inherently self-shedding.

In addition to holding the cutter pin 130 (Figure 14) in a downwardly angled position, so that the cutting tends to take place below disc level, the ceiling 144 of the groove performs the function of damping the movement of the pin. High speed movies taken under actual operating conditions show that the pin 130 upon being released from an obstruction does indeed swing forwardly, due to its resilience and with a snakelike action, until it contacts the front wall 143 of the groove just as illustrated in Figure 16. Contact uetween the upper surface of the pin and the ceiling 144 ·>£ the groove, particularly in the region of the periphery, is assured because of the leveling action of cen30 - 20 trifugal force, that is, the tendency of centrifugal force to radially align the pin with its point of attachment. The force of the pin against the ceiling is not great enough to cause aggravated wear but is great enough to 5 produce a frictional drag which inherently inhibits oscillation of the pin through a wide angle after striking an obstruction by reason of the pin's inherent resilience. The result is to produce a more even and consistent cutting action in spite of striking of obstructions and in spite of the uneven growth of the grass being cut.

The wall portion 122 which is divided by the annular groove 160 to form concentric ribs 122', 122 is intersectioned by radially spaced recesses in the top surface of the disc and which extend downwardly to form radially-aligned saddle openings in the ribs. Thus referring to Figures 19 and 20, the disc, at each pin location, has recesses 171, 172 which penetrate downwardly into the ribs 122', 122 to form aligned, pin-receiving saddle openings 173,174. The recesses 171, 172 are shown in profile in Figures 21, 23. To reinforce the pin-receiving openings 173, 174, the annular groove 160 is radially bridged at each pin position by reinforcing walls 175,176. In order to achieve clearance of the pin between the reinforcing walls, the underside of the groove is provided with an upwardly extending recess 181, shown in section in Figure 22, and which axially overlaps the recesses 171, 172 to define a through-opening for the pin having the profile illustrated at 182, in Figure 24.

While the bottoms of the recesses 171, 172 and 181 may be circularly profiled, for reception of a pin of circular cross section, it is preferred to employ a pin of non-circular cross section as indicated at 190 in Figures - 21 26 and 27. As here shown the pin is of fluted construction having axially extending ribs 191-194, and provided with a head 195 and terminating in an end rip 196. Such a ribbed pin has a number of advantages, but it will suffice for present purposes to say that the pin shown in Figure 26, registered in the ribbed opening 182 shown in Figure 24, is non-rotatable in the opening so that the pin maintains a constant and predetermined orientation to provide a relatively narrow line of impact with the grass, while being reversible through 180°. By use of aligned saddle openings the pin may be positively anchored, and tightly cantilevered, using a minimum amount of material in the disc. Moreover, because of the saddle openings, the pin is gripped over only a limited amount of area, and on opposite sides, so that replacement of the pin is much easier than where the pin is wedged tight in an opening which encircles the pin.

Finally, the access provided through the lower recess 181 permits entry of a prying tool for pin removal in those instances where the head of the pin has become damaged.

The recesses 171, 172 and 181 can be readily formed in a two piece mold having mold sections Ml, M2 (Figure 28). The mold section Ml is provided with projections 171a, 172a, while the lower section has a projection 181a, corresponding to the similarly numbered recesses. It is preferred that the tips of the projections be of scalloped profile to produce a cruciform opening (182 in Figure 24) for keyed reception of the cross section of the pin, but the tips of the projections may be circularly profiled if desired.

In describing a preferred form of the invention, (which utilizes a groove 137, 138 or 139 or trumpet profile - 22 with a ceiling 144 in between) no mention has been made of the total area of the ceiling. Advantageously the ceiling area is limited so that it is no more than about two to three times the area of the pin projected upon the ceiling.

Thus referring to Figure 30, where the total cross hatched area of the ceiling is indicated at 144, such area should, not exceed the projected area of the pin, shown by the doubly hatched area, by a factor of more than 2 to 3. The result is to produce a notch which is sufficiently wide for adequate flexing of the pin as it strikes an obstruction, and upon rebound, yet sufficiently small so that the notch is not capable of serving as a pocket or pouch for catapulting small stones and other debris.

In the preferred form of the invention the pin is .5 recessed, as described, in a groove formed in the underside of the peripheral portion of the disc. However, it is not essential to provide a groove, and the invention may be employed in modified form as illustrated in Figures 31,32 and 32a where corresponding numerals have been employed with addition of subscript a. Thus the disc assembly has a disc-shaped body including a central portion 121a and a peripheral portion 123a, the central portion having a rotary drive connection 117a. Means indicated at 122a are provided for anchoring the pin 130a in a radially extending opening 127a which is angled downwardly at a shallow angle, with the tip portions of the pin projecting radially beyond and below the periphery of the disc. A backstop surface 142a (Figure 32) is arranged in the path of bending movement of the shank portion of the pin to support the pin as the projecting tip portion strikes an obstruction, and a corresponding frontstop surface 143a, pieferably curved, is placed in the path of forward movement oi the pin to support it upon rebound. A bridge, indicated - 23 at 147a, closely overlies the pin at the periphery of the disc. The bridge serves to hold the pin in a downwardly angled working position notwithstanding the elevating effect of the centrifugal force, while producing a dampening effect upon the pin by reason of frictional engagement with the ceiling surface 144 as the pin bends backwardly and forwardly below the bridge.

It is further within the scope of the present invention to provide the groove 137, 138 or 139 of the preferred embodiment of Figures 12-16, and in which the pin is recessed, with a floor thereby enclosing the groove on the underside. Such structure is illustrated in Figures 33 and 34, in which the floor surface is indicated at 200 opposed to the ceiling surface 144b and with all other corresponding elements being designated by corresponding reference numerals with addition of subscript b. By enclosing the groove on the underside, the groove is converted into a radially extending recess, completely enclosing the pin, while permitting swinging movement thereof between a backstop surface 142b and a front wall 143b.

The floor not only prevents entry of small stones which conceivably could become missiles, but it also provides additional frictional damping for the pin, while preventing the shank portion of the pin from moving downwardly beyond the undersurface of the disc. In short, the floor insures that the pin is at all times contained and fully protected in all directions. Finally, it will be understood that the integral floor 200 serves to further strengthen the disc structure. If desired, the floor may be extended radially outward to provide a lower protective ledge having the same profile of the ledge 161 (Figure 13).

In the various embodiments of the invention described above, the pin has an enlarged head and is intended to be inserted from the inside out. In one embodiment of the present invention provision is made for inserting a pin from the outside in by avoiding an enlarged head and by providing latching members for example, in the disc structure. Such a modified embodiment is shown in Figures 35 and 36 in which corresponding reference numerals, with addition of subscript c, are employed to indicate corresponding parts. In this embodiment the head 131c of the pin has the same diameter as the shank portion. The pin is engaged and retained by a pair of resilient latch members 201, 202 which may either be separate or integrally formed when molding the disc and which are oriented in inwardly-sprung positions engaging a reduced section 203 of the pin immediately under the head 131c, Upon insertion head first, when the head strikes the latch members 201,202 they are cammed outwardly and then snap into the reduced section 203 to hold the pin firmly in place against the effects of centrifugal force. When pin replacement is necessary the old pin may be squarely severed at the periphery of the disc and tapped inwardly by means of a drift pin or the like, thereby freeing the opening for insertion of a new pin. This may be accomplished without having access to the top of the disc so that the disc need not be removed from the mower for pin replacement.

While it is preferred to employ a wall 22, 122 for mounting the pins which is of continuous, annular shape, it will be understood by one skilled in the art that the wall may be non-circular, for example, of polygonal shape, if desired. Also the wall may be discontinuous, that is, in the form of a short segment of a circle or polygon and either curved or straight without departing from the invention. Thus the term circular center portion of the disc refers generally to that portion which immediately - 25 surrounds the hub and which need not be circularly bounded by the wall. Indeed, the term wall refers to any upstanding structural means on the disc, either integral with the disc or not, for engaging and thus rigidly securing to the disc, in generally radial position, the shank portions of the respective pins. Similarly, the term annular outer portion of the disc is directed to a portion having an outer edge which has a sufficiently gradual curvature so that it is impossible for the outer edge of the rotating element to strike a hammer blow against a pebble or piece of debris sufficient to turn the same into a missile. The terms disc” and disc assembly refer to a shape which sufficiently approaches a smooth circular shape so that the member is incapable of being blocked by, or striking a direct hammer blow against, a concentrated obstruction.

The term stiffly resilient has been used to characterize the long, flexible tip portion of the cutter pin. This term has been used in order to distinguish over rigid and relatively non-yielding, or backed-up, cutting elements which have been used in the prior art and which are capable of inflicting serious injury upon the hand or foot of the operator. The term is also used to distinguish over filamentary cutting elements, for example formed of nylon, which are relatively limp, which tend to sag under their own weight or rely upon centrifugal force to keep them in a cutting posture. Indeed, the pin is stiff enough so that the tip remains downwardly angled, to cut at or slightly below disc level in spite of the elevating, or leveling, effect of centrifugal force. It is nevertheless of sufficiently low mass, and sufficiently resilient and yielding so as to retreat to an out-of-the-way position upon striking an obstruction ir eluding the hand or foot of the operator. While the tip is capable of applying a painful blow to an exposed limb, severe injury of the type inflicted - 26 172 by a steel blade is avoided.

It has been found preferable to use a type of plastics material for the cutter pins which has a resilient, elastic nature, which is flexible in this section, which resists surface abrasion, which has a high impact strength which resists notching and is capable of repeated stressing without fatigue. Various forms of nylon manufactured, for example, by Ε. I. duPont de Nemours possess the above characteristics in desired combination. However, it is .0 found that nylon is not the only material which can be successfully employed and DELROM (Registered Trade Mark) (acetyl homopolymer), also manufactured by duPont, may be successfully used. Poly carbonate and phenylene oxide plastics materials sold respectively under the Regis.5 tered Trade Marks Lexan and Noryl and manufactured by General Electric Company, are also plastics having high performance characteristics and which may be expected to have a long life in the present usage. Common varieties of polyethylene and polypropylene will also serve and have the advantage of economy. The plastics materials which have thus far been acceptable for cutter pins have the following approximate minimum mechanical properties: tensile strength 8,000 psi; compressive strength 11,000 psi; flexural yield strength 6,000 psi. ; and flexural mod5 ulus 100,000 psi.

While it is preferred to employ a pin having an enlarged head with a cylindrical shank portion adjacent thereto and a flexible tip portion of constant taper, it will he apparent to one skilled in the art that the inven3 tion is not limited to the particular shape which is disclosed. Indeed, instead of using a constant taper resulting in a sharp conical shape, with straight, convergent sides, the sides may be slightly concaved, or even slightly convexed if desired. Because of the variations in shape 43173 - 27 the terms shank portion and tip portion, as applied to a given structure, may shift or overlap. Generally stated, the shank portion is the portion which is permanently within the confines of the disc whereas the tip portion may be defined as that portion which normally extends beyond the disc. By taper is meant gradual reduction in area free of any abrupt changes in cross section. The diameter of the tip portion, near the outer tip 38 of the pin, is, for the most common size of mower, on the order of 0.050 to 0.125 inch, preferably about 0.09 inch, providing a cross sectional area of about .0064 square inch. Pins having a shank diameter of about 0.250 to 0.375 inch have been used, corresponding to a cross sectional area of about 0.049 to about 0.110 square inch. The average thickness of the pin should preferably be greater than 0.20 Inch. In the case of a tapered pin, the shank portion of the pin should have a cross sectional area which is at least four, and preferably about five to ten, times that at the outer tip. The size of the pin may be scaled downwardly, in proportion, for a hand held weed trimmer, or may be scaled upwardly, for heavy work, where higher horsepower is available.

The invention is not limited to any particular cross section, and the cross section may be round, oval, star-shaped, square, or even somewhat rectangular provided there is sufficient cross section so that the tip portion of the pin can be characterized as stiffly resilient. The term head is not necessarily limited to an enlargement and is intended, more generally, to denote the inner end of the pin, provided that suitable retaining means are used to hold the pin anchored in the disc. Thus it is possible, within the scope of the invention, even - 28 though not preferred, for the head portion of the pin to be threadedly retained in its registering opening. The term plastics includes tough flexible materials having a density which is characteristic of synthetic plastics in general, exhibiting abrasion resistance comparable to the high performance synthetic materials already mentioned and capable of self-restoration to substantially radial position after bending at right angles around a curved backstop.

In carrying out the invention, the disc itself has been manufactured from plastics materials having characteristics similar to those materials used in the cutter pins and capable of resisting abrasion while resiliently deforming, for purposes of self-protection, in the face of suddenly applied impact as, for example, upon the striking of a sharp embedded object when rotating at rated speed. However, durable materials other than plastics for example, steel, may be used for the disc. A typical disc, in a push type mower powered by a 3 horsepower engine and designed to cut a 20 inch wide swath, is 14 inches in diameter with cutter pins mounted in the disc as shown in Figures 2 and 12, each pin being about six inches long. Such disc and pin assembly will have rotational inertial equal to or somewhat less than that of the usual unitary steel blade. A disc, with pins installed to make the effective cutting width 20 inches has been operated at a rotational speed on the order of 3,000 rpm. and has been found capable, in heavygrass or weeds, of fully utilizing the rated horsepower of the usual (3-4 hp.) engine, with the pins automatically yielding under load to prevent lugging or stalling of the engine upon engagement of heavy wetted vegetation. Thus the construction may be distinguished from 43173 - 29 the prior art in which stalling of the engine is a common occurrence. The construction is distinguished, by equal margin, over whirling filament cutters which are suited primarily to hand held trimmers.

The invention has been described in connection with a rotary lawn mower where it finds greatest utility, being sufficiently versatile as to be used in rotary mowers already in the field as well as in new designs of rotary mowers, replacing in each the sharpened steel blade which has for many years been used as a standard cutting element. Thus the term mower as used herein includes weed cutters, trimmers and edgers for example of the light hand-held type powered by an electric motor.

Claims (35)

1. CLAIMS:I. A cutter disc assembly for a rotary lawn mower having a vertiqal drive shaft comprising, in combination, a disc having a central portion with provision for connection to the lower end of the drive shaft and a peripheral portion presenting a generally horizontal or frusto-conical surface on its underside, at least one cutter pin carried by said disc and arranged generally radially of the disc each pin being made of a tough, resilient abrasionresistant plastics material and having a head, a shank portion adjacent the head, and a tip portion merging with the shank portion, mounting means provided by the disc for engaging and supporting the shank portion of each pin cantilever-fashion so that the tip portion of the pin projects radially outwardly of the periphery of the disc in a stiffly resilient manner for cutting of the grass as the disc is rotated, the mounting means being spaced inwardly of the disc periphery so that if the tip portion of the pin strikes a major obstruction radially of the disc the pin may bend into a curve configuration so that at least part of the tip portion of the pin moves to a position within the disc periphery, and means for ensuring that the curvature is smooth With avoidance of any sharply concentrated stress in the pin,and/or the pin being so constructed that when it is bent it assumes said smooth curvature,substantially the entire shank portion of the pin being situated above the underside surface of the peripheral portion of the disc and being generally parallel to or inclined at an angle of a few degrees to, the said underside surface so that the shank portion of the pin is shielded against obstructions axially engaging the underside of the disc. 43173 - 31

2. The combination as claimed in Claim 1 in which the tip portion of the pin upon striking a radial obstruction is free to bend so that any part of the tip portion may move to a protected position within the disc periphery so that the abrading effect of the obstruction primarily occurs at the edge of the disc rather than at the surface of the pin.

3. The combination as claimed in Claim 1 in which the central portion of the disc is offset axially from the peripheral portion to form a shallow vertically extending wall, the pin being fitted for cantilever support in a radial opening formed in the wall.

4. The combination as claimed in Claim 3, in which the disc is recessed on its underside adjacent the head of the pin to provide access to the head of the pin enabling it to be inserted into and withdrawn from the opening.

5. The combination as claimed in Claim 1 in which the cross section of the shank portion adjacent the head is non-circular and in which the opening is of registering non-circular section to prevent twisting of the pin about its axis.

6. The combination as claimed in Claim 5 in which the cross section is such as to permit insertion of the pin in two positions rotated about the pin axis 180°.

7. The combination as claimed in Claim 2 in which the radial opening in tiie disc is formed by registering saddle recesses extending axially inwardly from opposite sides of the disc. 4 317 2 - 32

8. The combination as claimed in Claim 3 in which the wall is in the form of a pair of annular reinforcing ribs and in which the pin is in register with aligned radial openings formed in the wall,

9. The combination as claimed in Claim 1 in which the pin is pushed into a radial opening in the disc and in which the shank portion of the pin is dimensioned for insertion of the pin radially inwardly, and a latch interposed between the disc and the head of the pin to retain it in the opening against the pull of centrifugal force,

10. The combination as claimed in Claim 1 in which the disc provides a bridge above the pin adjacent the periphery of the disc, the bridge having a generally horizontal ceiling surface spaced closely to the shank portion of the pin and which extends peripherally permitting lateral swinging movement of the pin while inhibiting upward movement of the pin and thus holding the tip portion of the pin down to the work as the disc rotates. ll.. The combination as claimed in Claim 1 in which the pin is angled downwardly at a few degrees to the horizontal so that the outer tip of the pin extends below the level of the disc.

11. 12. The combination as claimed in Claim 11 in which the angle is between 2 and 8 degrees.

12. 13. The combination as claimed in Claim 11 in which the disc provides a bridge above the pin adjacent the 4317® - 33 periphery of the disc, the bridge having ceiling surface adjacent to the shank portion of the pin tending to hold the pin in its downwardly angled position notwithstanding the leveling effect of centrifugal force upon the pin as the disc rotates, tending to make the pin horizontal.

13. 14. The combination as claimed in Claim 10 in which the ceiling is bounded by backstop and frontstop surfaces provided in the path of the bending movement of the pin upon striking of an obstruction.

14. 15. The combination as claimed in Claim 14, in which the backstop and frontstop surfaces are curved and outwardly flaring in a general direction away from the rotary axis of the disc.

15. 16. The combination as claimed in Claim 10 in which the bridge is provided with a ledge which extends beyond the generally circular periphery of the disc to form a protective recess into which the tip portion of the pin bends upon striking an obstruction.

16. 17. The combination as claimed in Claim 1 in which the means for ensuring that the curvature is smooth includes a backstop mounted on the disc in the path of rearward bending movement of the pin as the tip portion of the pin strikes an obstruction.

17. 18. The combination as claimed in Claim 17 in which the backstop is smoothly curved in a direction away from the direction of the disc rotation to provide support for the pin distributed along the length thereof.

18. 19. The combination as claimed in Claim 18 in which the backstop stops short of reaching the periphery of the disc so that the tip portion of the pin upon - 34 striking an obstruction is free to move into the confines of the disc for protection thereby.

19. 20. The combination as claimed in Claim 18 in which the periphery of the disc is provided at the pin position with a ledge which extends beyond the periphery of the remainder of the disc to form a protective recess into which the tip portion of the pin bends upon striking an obstruction.

20. 21. The combination as claimed in Claim 20 in which the ledge is formed by a bridge extending beyond the periphery of the remainder of the disc.

21. 22. The combination as claimed in Claim 17 in which a frontstop is provided on the disc mounted in the path of forward movement of the shank of the pin to ensure that the curvature of the pin is smooth as the pin rebounds from the backstop after the striking of an obstruction.

22. 23. The combination as claimed in Claim 22 in which tne frontstop is smoothly curved. 21. The combination as claimed in Claim 1 in which t.ie means for ensuring that the curvature of the pin is smooth includes a smoothly curved backstop and a smoothly curved frontstop located in the paths of opposite movement of the pin.

23. 25. The combination as claimed in Claim 1 in which the pin is constructed so as to have a tapering configuration , with the pin being of large cross section at the head and with the shank portion tapering to a thin - 35 cross section in the tip portion, so that when the pin is bent, it assumes said smooth curvature.

24. 26. The combination as claimed in Claim 25 in which the shank portion of the pin has a cross sectional area which is at least about four times as great as that of the outer tip of the pin.

25. 27. The combination as claimed in Claim 1 in which the cutter pin projects radially from the periphery of the disc by a distance of one half to three inches.

26. 28. The combination as claimed in Claim 1 in which two to four pins are provided spaced symmetrically on the disc,

27. 29. The combination as claimed in Claim 1 in which the pin occupies a radial groove formed on the underside of the disc, the groove having an arcuate dimension sufficient to permit said bending of the pin when the tip portion thereof strikes an obstruction.

28. 30. The combination as claimed in Claim 1 in which the disc includes a radially extending recess having outwardly flaring back and front walls in the path of movement of the pin serving as a backstop and frontstop for limiting and distributing the bending movement of the pin as the tip portion of the pin strikes an obstruction.

29. 31. The combination as claimed in Claim 30 in which the recess has a trumpet-shaped horizontal profile having a width at its throat just sufficient to accommodate the shank portion of the pin. - 36

30. 32. The combination as claimed in Claim 29 in which the radial groove has a trumpet-shaped profile having a width at its inner end and having an axial depth just sufficient to accommodate the shank portion of the pin for shielding the shank portion of the pin against axially-engaged obstructions.

31. 33. The combination as claimed in Claim 29 in which the ceiling of the groove at the periphery of the disc engages the pin in its course of bending to dampen the movement of the pin.

32. 34. The combination as claimed in Claim 30 in which the recess has a ceiling which is angled downwardly by a shallow angle in the radial direction, the ceiling closely overlying and engaging the pin at the periphery of the disc thereby tending to hold the tip portion for cutting at a level below the bottom of the disc notwithstanding the leveling effect of centrifugal force upon the pin.

33. 35. The combination as claimed in Claim 1 in which upstanding, upwardly sweeping radial vanes are formed on the upper surface of the disc.

34. 36. The combination as claimed in Claim 1 including a step on the outer periphery of the disc, the step being adjacent the pin, the step being oriented so that the disc radius before the step is greater than the disc radius following the step as the disc is rotated in its intended manner, whereby the step forms a protective recess into which the tip portion of the pin bends upon striking an obstruction. - 35. 37 37. The combination as claimed, in Claim 10 in which the means ior ensuring that said curvature of the pin is smooth includes a backstop mounted on the disc in the path of rearward bending movement of the pin as the 5 tip portion of the pin strikes an obstruction. 36. 38. The combination as claimed in Claim 10 in which the pin is constructed so as to have a tapered configuration with the pin being a relatively large cross section at the head and with the shank portion tapering 10 to a relatively thin cross section in the tip portion, so that when the pin is bent it assumes said smooth curvature.

35. A cutter disc assembly, for a rotary lawn mower having a vertical drive shaft, substantially as herein15 before described with reference to and as illustrated in the accompanying drawings.