Grass-cutting head with spiral guide channels for the cutting line

The grass-cutting head (101) has a body (103) forming a housing for at least one spool of cutting line (F1; F2), provided with at least one outlet hole (111) of an end of the cutting line wound on said spool positioned inside the head. For each outlet hole, a guide channel for the cutting line is also provided, extending from the inside of the housing towards the hole and having an inclined trend, gradually moving away from said axis of rotation.

TECHNICAL FIELD

The present invention relates to a grass-cutting head for cutting vegetation, and more specifically to a grass-cutting head of the line type, that is, in which the cutting member is composed of a line projecting radially from the head, and which cuts the surrounding vegetation through centrifugal force.

STATE OF THE ART

For gardening jobs, both at amateur and professional level, grass-cutting heads are commonly used to cut grass and other vegetation, provided with cutting lines projecting radially from a main body of the head and which, thanks to the centrifugal force exerted thereon and to the rapid rotation of the head about the axis thereof, cut the vegetation.

In conventional grass-cutting heads, the outlet hole of the cutting line can be produced directly in the body forming the housing of the line spool (as in U.S. Pat. No. 4,148,141), or in metal bushings inserted in respective seats produced in the perimeter wall, typically cylindrical, of the body housing the spool (U.S. Pat. No. 4,097,991).

U.S. Pat. No. 4,271,595 describes a grass-cutting head of the line type wherein two cutting lines project from the body of the head inclined with respect to the radial direction. For this purpose the bushings defining the outlet holes of the lines have a channel for the lines to pass through with a rectilinear but substantially inclined trend with respect to the radial direction, instead of being parallel to said direction as in the case of conventional grass-cutting devices. This particular arrangement has the function of reducing wear and overheating of the line at high head rotation speeds. The hole of the bushing opens onto the cylindrical surface of the body of the head.

In all conventional heads, including the head produced as indicated in U.S. Pat. No. 4,271,595, the cutting line is subject to frequent breakages due to high impact against any obstructions which may be present around the grass-cutting head (such as stones, clods of hard soil or the like) and also due to any particularly coarse vegetation present. Breakage of the line often occurs at the level of the hole through which the line is fed from the body forming the housing for the spool on which the cutting line is wound. When this occurs, considerable difficulties can be encountered when passing a new portion of line required to continue with the cutting operation through the hole. In particular, if the spool accidentally rotates even by a slight angle after breakage of the line, the severed end of the cutting line retracts completely inside the body of the head and said body must be opened to pass the end of the line into the bushing or hole to make it project from the body of the head through said hole by a length sufficient to allow correct operation of the lengthening devices with which grass-cutting heads are normally provided.

U.S. Pat. No. 4,114,269 describes a grass-cutting head of the line type, wherein the outlet hole of the cutting line is delimited by two rectilinear edges, parallel to the axis of rotation of the head. The front edge, or the edge farther forward with respect to the direction of rotation of the head, has a tear-drop shaped cross section, that is, which is thicker than the remaining part of the approximately cylindrical wall of the body housing the cutting spool, in which wall the outlet holes of the cutting line are produced. This conformation has the object of reducing strains and overheating of the line, but does not overcome the aforesaid drawbacks, related to retraction of the broken end of the line into the housing of the spool.

OBJECTS AND SUMMARY OF THE INVENTION

The object of the present invention is to produce a grass-cutting head which overcomes entirely or in part the aforesaid drawbacks and which in particular reduces the tendency of the line to break due to impact with obstructions surrounding the head during cutting and/or facilitates projection of the line, even if it breaks at the level of the outlet hole, or at the level of the outlet bushing from the body of the head.

These and other objects and advantages, which shall be apparent to those skilled in the art from reading the text hereunder, are obtained in substance with a head as claimed in claim1, The dependent claims relate to further possible and advantageous features of the invention.

In substance, the invention provides a grass-cutting head with an axis of rotation and a body forming the housing for at least one spool of cutting line, provided with at least one outlet hole of an end of said cutting line wound on said spool, which also comprises, for each hole, a guide channel for the cutting line, extending from the inside of said housing towards the outlet hole and having an inclined development, gradually moving away from said axis of rotation. According to an advantageous embodiment, the outlet hole is on a surface inclined by an angle differing from 90° with respect to a radial plane containing the axis of rotation and passing through the center of the hole. In substance, in the preferred embodiment, the hole or each hole is located on a surface which intersects a substantially cylindrical wall of the body of the head.

In practice, the channel is produced in portions of the body of the head which project gradually with respect to a basic shape substantially with a circular section of said body and the line is fed from said projections with a non-radial orientation, but inclined with respect to a radial plane. In this way improved operation of the head is obtained, with regard to the consequences of impact with possible obstructions around the head during operation.

In a practical embodiment, the outlet hole or each outlet hole can define a direction of projection of the line from the body of the head inclined by an angle between 30° and 90° and preferably between 60° and 90° with respect to a radial direction.

The guide channel of the cutting line can have, preferably, an approximately spiral shape, where spiral is intended generally as a curve which has a variable radius of curvature to move gradually away from an axis or center, coincident with the axis of rotation of the grass-cutting head.

Preferably, the surface on which the outlet hole is located forms with said radial plane an angle between 0° and 80°, preferably between 0° and 45° and even more preferably between 0° and 30°.

According to a possible embodiment of the head according to the invention, associated with each of the outlet holes of the line are respective tangential tabs, projecting with respect to the body of the grass-cutting head. These tabs (advantageously arranged on the projections inside which the guide channels of the lines are produced) can be interchangeable and optionally provided with toothing, i.e. serrated on the surface radially facing towards the outside of the head.

In a possible embodiment, in a top plan view the body of the head has a substantially circular shape and, for said hole or for each of said holes, integral with said body is a projection with a radially increasing extension, inside which said guide channel extends. The profile of the projections is preferably approximately a portion of spiral.

In a possible embodiment, the body of the grass-cutting head comprises: a cup portion, defining a housing for the spool of cutting line; an annular portion coupled to said cup portion, defining, together with said cup portion, said guide channel or channels; and a removable closing member.

According to an advantageous embodiment, each of said guide channels extends along an angle equal to at least 30°, preferably equal to or greater than 45° and even more preferably equal to or greater than 60°, for example also between 80° and 120°, about the axis of rotation of said grass-cutting head.

According to a different aspect, the present invention relates to a grass-cutting head with an axis of rotation and a body forming a housing for at least one spool of cutting line, provided with at least one outlet hole of an end of said cutting line wound on the spool, which has a toothed outer profile, a respective outlet hole of the cutting line being positioned at the level of each tooth of said profile. The grass-cutting head as a whole will therefore no longer have, in a top plan view, the conventional circular shape, but will be characterized by the projections forming said teeth, at the level of which the line projects with a non-radial direction of projection.

In practice, each tooth of said toothed profile has a first side inclined by an angle not exceeding 45° and preferably between 0° and 30° with respect to a radial direction, on which the respective outlet hole of the line is produced. Moreover, according to a preferred embodiment of the invention each tooth has a second curvilinear side with a preferably approximately spiral development. A guide channel for the cutting line extends inside each of said teeth.

With initial reference toFIG. 1 to 4, in a first embodiment the grass-cutting head according to the invention, indicated as a whole with1, has a body3composed of a main part substantially in the form of a casing, shown inFIGS. 1 to 4, and optionally a closing cover, not shown, which defines with the cup portion, a compartment13to house a spool, indicated schematically with5(FIGS. 2 and 4), on which one or more cutting lines F1, F2, are wound. Externally, the body3of the grass-cutting head1has a substantially circular extension in a top plan view, the maximum diameter of which is defined by the diameter of a circular flange7. Extending under the circular flange7, with basic conformation with a substantially circular section of the body3, are two projections indicated with9.

These projections have an approximately spiral development, in the sense that they are defined by an external curvilinear surface9A which moves gradually away from the body of the head3, from a point9B of connection with the cylindrical wall of the body3, to a point9C of maximum radial distance from the axis of rotation A-A of the grass-cutting head. Moreover, each projection9has a flat surface (in the example shown) indicated with9D, which has an inclination of an angle β (FIG. 2) with respect to a radial plane, that is, a plane containing the axis of rotation A-A, passing through the central area of the surface9D. The angle formed by the direction of projection of the cutting line F1, F2with respect to the radial direction, is indicated with γ. The sum of the angles β and γ can be equal to 90° if the line projects orthogonally to the frontal surface9D of the projection9, but this is not binding, as can be seen in the example shown.

In practice, the projections9form teeth projecting from the body of the grass-cutting head1, which in the example shown have sides (9A,9D) differing from each other in shape and/or inclination.

In an approximately central position the surface9D has a hole11from, which the cutting line F1or F2project. In the example shown the hole11is produced directly in the base material forming the body3(or the lower part of said body) and the projections9. It would also be possible for the hole11to be formed in a bushing inserted inside the base material forming the projection9and/or the body3.

As can be seen in particular inFIGS. 2 and 4, both a housing, indicated with13, for the spool5, and a pair of guide channels15produced in the material forming the projections9extending more or less spirally, are defined inside the body3. Each of these channels has an inlet, which is radially innermost at the level of a rounded corner15A produced in the base material forming the body3, and an outlet at the level of the respective outlet hole11of the cutting line F1or F2, said hole defining the radially outermost point of the channel. Alternatively, the channels can be made of a different material to the base material of the head of the body, for example by metal inserts inserted in an injection mold for plastic materials. The projections9can also be made of the same material as the body3or of a different material, optionally molded together with the body3or by inserts arranged in the mold prior to injection of the resin with which the body3can be made. Alternatively, the head can be made of metal parts.

Each guide channel15therefore extends for an angle α (FIG. 2) about the axis of rotation A-A of the grass-cutting head. The line F1, F2projects with the free end thereof from the respective hole11in a direction which substantially forms the extension of the spiral defining the median line of the channel15. It must be understood that spiral shape is intended herein not necessarily as a spiral in a mathematical or geometric sense, but in the more general sense a shape of the channel15, wherein this extends from the inlet (at the level of the edge15A) to the outlet formed by the hole11extending gradually away from the axis A-A in a radial direction outwards. If necessary, the channel15could have a conformation which is rectilinear or formed of rectilinear portions with gradually variable angles from the inlet to the outlet.

With this configuration two positive effects are substantially obtained. On the one hand, when the head rotates (the direction of rotation is indicated with the arrow F inFIG. 1) the side surface, that is the side9A of each of the two projections9, tends to move any obstructions, such as stones, clods of hardened soil, particularly coarse vegetation or the like, away from the hole11so that these obstructions do not knock against the line F1or F2too close to the point at which it projects from the grass-cutting head1. This means that any breakage of the line caused by a violent impact against an obstruction occurs at a certain distance from the outlet hole11, thereby avoiding the risk of the free end of the severed line remaining inside the body3of the head1.

In the second place, even if breakage of the line were to take place at the level of the hole11, subsequent projection of a new portion of line F1, F2, to restore the cutting function of the grass-cutting head1, would nonetheless be possible thanks to the fact that a large portion of the last turn of cutting line F1, F2inside the grass-cutting head1is guided in the respective spiral channel15. Contrary to the case of conventional heads, therefore, even if the line were to break close to the wall of the head and, therefore, to the hole11, this would not make it impossible to restore the cutting length of the said line.

The angular extension α of the guide channel15does not necessarily have to be as wide as shown inFIGS. 1 to 4(here approximately equal to or slightly greater than 90°). On the contrary, this angle can also be equal to 60° or less, although a relatively wide angle is particularly useful to guarantee the second function described above.

FIGS. 5 and 6show, in a perspective view and in a bottom plan view according to VI-VI inFIG. 5, a slightly modified embodiment of the head described above. The same numbers indicate the same or equivalent parts to those of the previous embodiment. In this case, the body3of the head, or more precisely the lower part of said body, has four projections9rather than two, so that four cutting lines (not shown) can project from the respective holes11on the grass-cutting head1. In this case the angle α along which the four guide channels15extend will be slightly below 90°.

FIG. 7 to 14show an improved embodiment of the head according to the invention. The head, indicated as a whole with101, has a body103formed by a cup portion103A, an annular portion103B coupled permanently to the portion103A (i.e. even by gluing, welding or the like, or with screws, rivets, pins or in another way) and a cover103C removable to allow access to the inside of a compartment housing the spool of cutting line. This compartment is defined by the portions103A and103B of the body103. In this embodiment, the spool, indicated with105, is produced as shown in U.S. Pat. No. 6,851,191, the content of which is explicitly referred to here as an integral part of the present description, and which can be referred to for further constructional details.

Inside, this spool105is an elastically stressed slider106, cooperating with a double series of toothings produced on the inside of the hub of the spool105, to allow lengthening of the line wound on said spool. The slider106slides axially on a pin108torsionally coupled to the portion103A of the body103of the head. There is a torsional coupling also between the slider106and the pin108composed of a series of grooves108A (FIG. 7) on the pin108and corresponding teeth on the slider106. The movement according to the double arrow f106of the slider106is obtained by a button110projecting through a hole103D produced in the central part of the cover103C. The button110projects downwards from the head, when this is mounted on the brush cutter or other operating device, so that the user can press the rotating head on the ground and thereby cause repeated actions of alternate sliding on the slider106and consequent lengthening in steps of the cuffing line wound on the spool105, all as described in greater detail in the aforesaid U.S. Pat. No. 6,851,191.

The cover103C has elastic tabs103E with which it connects in notches103F produced in the annular portion103B of the body103of the head. The elastic tabs103E are accessible from the outside (FIG. 8) so that, by means of pressure thereon, the cover103C can be released from the body103formed by the portions103A,103B of the head101.

Once the portions103A and103B of the body103of the grass-cutting head101are coupled together they define a body having a basic extension with a substantially circular section, from which projections109, produced in part on the portion103A and in part on the portion103B of the body103, project in a radial direction. The projections109have an approximately spiral conformation, in the sense that their surface or side wall109A has an approximately spiral trend (in the plan view), moving gradually away from the axis A-A of rotation of the head starting from a point109B of connection to a substantially cylindrical surface of the central body103until reaching an area109C of maximum radial dimension. Each projection109also has an approximately radial surface109D onto which a respective outlet hole111of the cutting line opens. The direction of exit of the cutting line is therefore in this case substantially tangential, that is, substantially orthogonal to a plane passing through the axis of rotation A-A of the head.

The projections109are produced as mentioned above in part in the material forming the portion103A and in part in the material forming the portion103B of the body103(seeFIG. 7). Coupling of these two portions forms a channel115through which the respective cutting line (not shown) is guided. In substance, each of the two channels115extends from a rounded corner115A with a substantially spiral extension to the front surface109D of the respective projection109.

In the example shown respective tangential tabs, which in this specific embodiment are interchangeable, are associated and made integral with each of the two projections109. For this purpose, each tab121has a system for connection to i.e. reversible engagement with the body103of the grass-cutting head101. To obtain this reversible engagement, in the embodiment shown, each tab121has a first hook-shaped end121A which is inserted into a corresponding recess131produced in the projection109. The opposite end121B of each tab121has a through hole121C (i.e. shaped like an eyelet) and is positioned at the level of the outlet hole111of the cutting line. As can be seen in particular inFIG. 9, in this embodiment the interchangeable tab121actually forms one side of the hole111. Due to how the tab121is positioned, the end121B thereof defines a supporting surface for the cutting line.

Each tangential tab121is connected to the respective projection109by first inserting the hook shaped end121A into the corresponding recess131and then inserting the entire interchangeable tab into the seat defined between the two coupled portions103A,103B. A pin, a screw or the like is inserted into a hole133of the projection109, which is in alignment with the through hole121C of the respective tab121. The tangential tab121is thus permanently fastened to the head until subsequent removal of the screw, pin or the like inserted in the hole133, to allow replacement of the tab121, for example due to wear.

As can be seen in particular inFIGS. 7 and 8, once the portions103A,103B and the tabs121have been assembled, the guide channel115is actually delimited in part by walls formed of the material of which the body103(more specifically the portions103A,103B thereof) of the grass-cutting head101is composed and in part by the radially inward facing surface121E (FIG. 7) of the respective tangential tab121.

It would also be possible to omit the tabs121and to produce the body103of the head101solely with two portions103A,103B coupled to each other, besides the cover103C. The outlet hole111of the line could also be defined in a bushing, possibly made of metal, inserted in the material forming the respective projection109. However, the use of interchangeable tangential tabs121is particularly advantageous because it allows worn tabs to be replaced with new ones, preserving the integrity of the body103of the head. Tabs made of a sturdier material than the material forming the body103of the grass-cutting head101allow the useful life of the head to be prolonged even if they are not interchangeable, thanks to their increased durability. For example, the tabs could be made of metal and the rest of the head of molded synthetic resin. The increase in cost which this implies compared to a head entirely made of synthetic resin is slight, as the tabs have a limited mass. Alternatively, the tabs could be made of the same material as the body103. In this case, they form a sort of deposit of material which, although becoming worn, protects the remaining part of the head from premature wear.

Moreover, it is also possible to use interchangeable tangential tabs121of a different shape depending on the type of vegetation to be cut. For example, when cutting particularly coarse grass, it is possible to use tangential tabs121which have a toothing on the surface facing radially outward, said toothing performing severing of coarser vegetation.

In any case, the tangential tabs121offer further protection against breakage of the cutting line caused by impact thereof against obstructions present which may be found around the grass-cutting head during use.

FIG. 15shows a perspective view of the head inFIGS. 7 to 14, modified as regards the form of the tabs, here indicated with121X. The same numbers indicate the same or equivalent parts to those inFIGS. 7 to 14. The tabs121X are produced, in this case, with an outer toothing121D. This toothing has the function of severing or weakening the vegetation or other obstructions, such as clods of earth, which may be found around the head during use thereof, so as to perform a mechanical action preliminary to the cutting action of the line F1, F2.

FIGS. 16 and 17show a different configuration of the head, wherein the outlet holes of the cutting line are radial rather than inclined towards the tangential direction. As can be seen inFIG. 17, which represents a section along a plane separating the portions3A and3B of the body3of the head, housed therein is a spool5wound on which is the cutting line which projects through radial holes produced in bushings201inserted in the body of the head1. Between the spool5and each outlet hole of each bushing201a respective channel15is produced, substantially spiral in shape and defined by two surfaces15B,15C, the inlet of which is defined by a rounded corner15A. The shape of the channels15is substantially equivalent to that of the channels shown inFIGS. 1 and 2, with the difference that they end at the level of the bushings with radial outlet201.

It is understood that the drawing only shows an embodiment provided by way of a practical example of the finding, which may vary in forms and arrangements without however departing from the scope of the concept on which said finding is based.