TECHNICAL FIELD

The present invention relates to a cutting blade. More particularly, the present invention relates to a cutting blade for a garden tool.

BACKGROUND

Mower blades for cutting grass are well known in the art. Such mower blades are generally rotated by a prime mover to achieve a cutting action on grass. Generally, the mower blades are also provided with upturned wings to improve collection of cut grass.

However, during rotation, a turbulent air flow is generated around the wings due to shape and size of the wings, and high speed of rotation of the mower blades. Primarily, the turbulent air flow is caused due to sudden changes in shape of the cutting blades at the wings. Turbulent air flow leads to formation of vortices at the region of layer separation between air and edges of the wings. Consequently, high noise and drag force is generated. Drag force increases air resistance to the motion of the mower blades, resulting in more power required to rotate the mower blades at a given speed. Further, drag force also obstructs movement of particulate matter through air. This may decrease grass cutting and cut grass collection performance of the lawn mower.

In light of the foregoing, there is a need for a mower blade which at least partly reduces turbulence of air flow around the wings of the mower blade leading to generation of lower noise and less drag force. SUMMARY

In view of the above, it is an objective of the present invention to solve or at least reduce the problems discussed above. In particular, the objective is to provide an improved cutting blade which at least partly reduces turbulence of air flow. The objective is at least partially achieved with the rotatable cutting blade according to claim 1 . The rotatable cutting blade for a garden tool is adapted to rotate in a substantially horizontal plane when the garden tool is in use. Further, the cutting blade comprises two blade arms which extend in opposite directions substantially radially from a rotational axis, which extends in a vertical direction perpendicular to the horizontal plane. The blade arms each have a front edge in the horizontal plane, positioned in front, if viewed in the direction of rotation of the cutting blade, each front edge comprising a cutting edge. Each blade arm further comprises a back edge positioned in the back, if viewed in the direction of rotation of the cutting blade. Moreover, each blade arm also comprises a wing which extends, such that it rises from the horizontal plane, from the front edge towards the back edge. A streamline body is attached to each blade arm to distribute air flow around the blade arms during rotation of the cutting blade. Further, each streamline body is attached to the wing of each blade arm such that each streamline body extends behind the back edge of each blade arm, if viewed in the direction of rotation of the cutting blade. The streamline bodies may result in a more controlled air flow around the wings. Consequently, air may separate from the blade with less turbulence and vortices shed may be smaller with less energy. Thus, less noise may be generated during rotation of the cutting blade. The streamline bodies also may reduce drag force leading to lower air resistance to the rotation of the cutting blade and lower power required to rotate the blade at a given speed. Lower air resistance also may reduce obstruction to a movement of particulate matter through air. Thus, a detrimental effect on cutting and collecting performance of the blade may at least partly be reduced.

According to claim 2, each streamline body that extends behind the back edge of each blade arm, if viewed in the direction of rotation, may taper in a direction opposite of the direction of rotation. The tapering of the streamline bodies, in a direction opposite to the direction of rotation, may provide a smooth path for air flow without any sharp corners. Further according to claim 3, each streamline body may taper to an acute edge. The acute edge may minimize the turbulence caused by a rotating blade. Thereby for instance noise and energy consumption may be reduced.

According to claim 4, each wing may extend such that it rises from the horizontal plane from the front edge towards the back edge of each blade arm, such that a space may be created between each wing and the horizontal plane. Further, each streamline body may extend such that it at least partly fills the space between each wing and the horizontal plane. An empty space between a wing and the horizontal plane may cause unwanted turbulence. By filling that space with a streamline body, the turbulence may be reduced.

According to claim 5, a bottom surface of each streamline body may extend such that it rises from the horizontal plane towards a back edge of the streamline body, if viewed in the direction of rotation of the cutting blade. By raising the bottom surface of the streamline body, a smooth form of the bottom surface may be achieved that further reduces the turbulence caused by the rotating blade.

According to claim 6, each front edge, from an end portion of each blade arm, radially closest to the rotational axis, towards an end portion, radially remote from the rotational axis, may have a curved shape towards the direction of rotation. This may lead to an improved cutting performance of the cutting blade.

According to claim 7, each back edge from an end portion of each blade arm, radially closest to the rotational axis, towards an end portion, radially remote from the rotational axis, may have a curved shape towards the direction of rotation.

According to claim 8, a part of each streamline body that extends behind the back edge of each blade arm, if viewed in the direction of rotation, such that the back edge of each blade arm, at an end portion of the blade arm closest to the rotational axis, may form a substantially straight line with a back edge of each streamline body. Thereby an even back edge l i ne may be formed by the streamline body and the blade arm, such that there may be no sharp edges at the back edge that may cause turbulence. According to claim 9, a part of the back edge of each blade arm, at the location of the wing, may extend behind a part of the back edge of each blade arm, at an end portion of each blade arm radially closest to the rotational axis.

According to claim 10, each wing may extend such that it rises from the horizontal plane towards the back edge of each blade arm, at an end portion of each blade arm radially remote from the rotational axis.

According to claim 1 1 , a bottom surface, at the front edge of each blade arm, together with a bottom surface, of at least a part of each streamline body, may form a substantially common plane.

According to claim 12, each blade arm at the front edge may extend to decline from an end portion of each blade arm, radially closest to the rotational axis, towards an end portion of each blade arm, radially remote from the rotational axis.

According to claim 13, each blade arm and streamline body may have a thickness in the vertical direction , wherein the maximum thickness of each streamline body may be larger than the thickness of the blade arm.

According to claim 14, each streamline body may be attached to the blade arms as a separate part from the blade arm. Alternatively, according to claim 15, each streamline body may be produced in one unit with each blade arm.

According to claim 16, the garden tool may be a lawn mower.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be described in more detail with reference to the enclosed drawings, wherein:

FIG. 1 A illustrates a top perspective view of a cutting blade, according to an embodiment of the invention;

FIG. 1 B illustrates a front perspective view of the cutting blade, according to an embodiment of the present invention;

FIG. 2 illustrates a perspective view of a straight cutting blade, according to an embodiment of the present invention; and FIG. 3 illustrates a perspective view of a cutting blade with upturned wings, according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

The present invention wi ll be described more ful ly hereinafter with reference to the accompanying drawings, in which example embodiments of the invention incorporating one or more aspects of the present invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those ordinarily skilled in the art. For example, one or more aspects of the present invention can be utilized in other embodiments and even other types of devices. I n the drawings, li ke numbers refer to like elements.

FIGS. 1A and 1 B illustrate perspective views of a rotatable cutting blade

100 (hereinafter referred to as the "blade 100"), according to an embodiment of the present invention. The blade 100 may be used in any type of garden tool, such as, but not limited to, a lawn mower, a portable trimmer, or the like. In addition, any shape, size or type of material may be used within the scope of the present invention. Further, the blade 100 may include one or more apertures (not illustrated in the figures) for attachment to a drive shaft of the garden tool. The drive shaft is driven directly or indirectly by means of a prime mover, for example, an internal combustion engine, an electrical motor, or the like.

As illustrated in FIGS. 1A and 1 B, the blade 100 is adapted to rotate in a substantially horizontal plane H about a rotational axis X in a clockwise direction during operation of the garden tool. The rotational axis X extends in a vertical direction substantially perpendicular to the horizontal plane H. It may be apparent to a person ordinarily skilled in the art that the direction of rotation is clockwise with respect to a particular view of the blade 100 and may change with different views of the blade 100. Further, the blade 100 includes two blade arms 102 and 104 that extend in opposite directions, substantially in radial directions, from the rotational axis X. Specifically, the blade arms 102 and 104 extend from end portions 106 and 108, which are radially closest to the rotational axis X, to end portions 110 and 112, which are radially remote from the rotational axis X. Each of the blade arms 102 and 104 has front edges 114 and 116 respectively. The front edges 114 and 116 are positioned in front if viewed in the direction of rotation of the blade 100. As illustrated in FIGS. 1A and 1 B, each of the front edges 114 and 116 extend from the end portions 106 and 108 to the end portions 110 and 112 respectively, substantially in the horizontal plane H. Further, each of the front edges 114 and 116 has a curved shape towards the direction of rotation of the blade 100 for better cutting performance. Additionally, each of the blade arms 102 and 104, at the front edges 114 and 116, curves downwards from the end portions 106 and 108 to the end portions 110 and 112. Thus, there is a difference in height between each of the end portions 106 and 108, and the end portions 110 and 112, in the vertical direction. However, the front edges 114 and 116 may be of any shape within the scope of the present invention. For example, the front edges 114 and 116 may be substantially straight (described in conjunction with FIGS. 2 and 3). Moreover, each of the front edges 114 and 116 includes cutting edges 118 and 120 respectively. As illustrated in FIGS. 1A and 1 B, each of the cutting edges 118 and 120 extends substantially along the whole length of the front edges 114 and 116 respectively. However, each of the cutting edges 118 and 120 may extend only partially along the length of the front edges 114 and 116 (described in conjunction with FIG. 3). Further, each of the blade arms 102 and 104 also includes back edges 122 and 124 respectively. The back edges 122 and 124 are positioned in the back if viewed in the direction of rotation of the blade 100. As illustrated in FIGS. 1A and 1 B, the back edges 122 and 124 extend from the end portions 106 and 108 to the end portions 110 and 112 of the blade arms 102 and 104 respectively. Further, each of the back edges 122 and 124 has a curved shape towards the direction of rotation of the blade 100. It may be apparent to a person ordinarily skilled in the art that the blade arms 102 and 104 are substantially mirror images of each other such that the cutting edges 118 and 120 are positioned in the front whereas the back edges 122 and 124 are positioned in the back with respect to the direction of rotation of the blade 100.

As illustrated in FIGS. 1A and 1 B, each of the blade arms 102 and 104 further includes wings 126 and 128. Each of the wings 126 and 128 extends from the front edges 114 and 116 towards the back edges 122 and 124 substantially at end portions 110 and 112 of the blade arms 102 and 104 respectively, radially remote from the rotational axis X. Since the front edges 114 and 116 lie substantially in the horizontal plane H, each of the wings 126 and 128 rises from the horizontal plane H towards the back edges 122 and 124 respectively. Therefore, each of the wings 126 and 128 rises to a height above the horizontal plane H in the vertical direction and simultaneously extends towards the back edges 122 and 124 substantially opposite to the direction of rotation and parallel to the horizontal plane H. The shape of the wings 126 and 128 results in a space between each of the wings 126 and 128, and the horizontal plane H. The wings 126 and 128 are provided to at least improve collection of cut vegetation (For example, grass clippings) by providing an aerodynamic lift to cut vegetation. As a result, deposition of cut vegetation on the ground is at least partly reduced and collection of cut vegetation in a container attached to the garden tool is facilitated.

As illustrated in FIGS. 1A and 1 B, streamline bodies 130 and 132 are attached to each of the blade arms 102 and 104 respectively. Each of the streamline bodies 130 and 132 extends behind the back edges 122 and 124 of the blade arms 102 and 104 respectively, if viewed in the direction of rotation of the blade 100. Further, each of the streamline bodies 130 and 132 tapers in a direction opposite to the direction of rotation. In particular, thicknesses of each of the streamline bodies 130 and 132, in both the horizontal plane H and the vertical direction, decrease in a direction opposite to the direction of rotation. As illustrated in FIGS. 1A and 1 B, each of the streamline bodies 130 and 132 tapers to an acute edge. Therefore, each of the streamline bodies 130 and 132 tapers to a point without any rounded corners. However, the streamline bodies 130 and 132 may taper to one or more rounded corners within the scope of the present invention. Each of the streamline bodies 130 and 132 also extends such that it may at least partly fill the space between each of the wings 126 and 128, and the horizontal plane H.

As illustrated in FIGS. 1A and 1 B, bottom surfaces 134 and 136 of the streamline bodies 130 and 132 respectively extend such that each of the bottom surfaces 134 and 136 rises from the horizontal plane H towards the back edges 122 and 124, if viewed in the direction of rotation of the blade 100. Moreover, each of the bottom surfaces 134 and 136 of the stream line bodies 130 and 132 together with each of bottom surfaces 138 and 140, at the front edges 114 and 116, of the blade arms 102 and 104, form a substantially common surface. Thus, at least a part of the front edges 114 and 116, and at least a part of the streamline bodies 130 and 132 together form a continuous smooth surface. The common surface may be a planar surface or a curved surface without deviating from the scope of the present invention.

As illustrated in FIGS. 1A and 1 B, a part of each of the streamline bodies

130 and 132 extends behind the back edges 122 and 124 of the blade arms 102 and 104 respectively, if viewed in the direction of rotation. Further, each of back edges 142 and 144 of the streamline bodies 130 and 132 forms a substantially straight line with the back edges 122 and 124 at the end portions 106 and 108 of the blade arms 102 and 104 respectively, radially closest to the rotational axis X. Thus, a part of each of the streamline bodies 130 and 132 smoothly merge with the back edges 122 and 124 of the blade arms 102 and 104.

Further, a maximum thickness of each of the streamline bodies 130 and 132 in the vertical direction is larger than a thickness of the blade arms 102 and 104 in the vertical direction. In particular, as illustrated in FIGS. 1A and 1 B, the thickness of each of the streamline bodies 130 and 132 at the back edges 142 and 144 is substantially larger than the thickness of the back edges 122 and 124 at the end portions 110 and 112 of the blade arms 102 and 104. Thus, the thickness of each of the streamline bodies 130 and 132 increases towards the back edges 142 and 144 to fill the space between each of the wings 126 and 128, and the horizontal plane H.

In an embodiment of the present invention, each of the streamline bodies 130 and 132 is attached to the blade arms 102 and 104 respectively as a separate part from the blade arms 102 and 104. The streamline bodies 130 and 132 may be attached to the blade arms 102 and 104 by various processes, for example, but not limited to, welding, brazing, soldering, adhesives, or the like. Further, streamline bodies 130 and 132 may be of metal, plastic, or any other material without departing from the scope of the present invention. The material of the streamline bodies 130 and 132 may be same as or different from the material of the blade arms 102 and 104. In an alternative embodiment of the present invention, each of the streamline bodies 130 and 132 is produced in one unit with the blade arms 102 and 104. For example, the streamline bodies 130 and 132 may be part of a single moulded unit and of the same material as the blade arms 102 and 104 and thus, the complete blade 100.

During operation of the garden tool, each of the streamline bodies 130 and 132 distributes air flow around the blade arms 102 and 104. The tapering of the streamline bodies 130 and 132 in a direction opposite to the direction of rotation provides a smooth path for air flow without any sharp corners. Further, the streamline bodies 130 and 132 smoothly merge with various parts of the blade arms 102 and 104. Thus, air flow around the wings 126 and 128 is more controlled. Consequently, air separates from the blade 100 with less turbulence and vortices shed are smaller with less energy. Thus, less noise is generated during rotation of the blade 100. The streamline bodies 130 and 132 also reduce drag force leading to lower air resistance to the rotation of the blade 100 and lower power required to rotate the blade 100 at a given speed. Lower air resistance also reduces obstruction to a movement of particulate matter through air. Thus, a detrimental effect on cutting and collecting performance of the blade 100 is at least partly reduced.

FIG. 2 illustrates a blade 200 with blade arms 202 and 204 having substantially straight front edges 214 and 216, and substantially straight back edges 222 and 224 respectively. Cutting edges 218 and 220 extend substantially along the whole length of the front edges 214 and 216 respectively. Further, as illustrated in FIG. 2, wings 226 and 228, and streamline bodies 230 and 232 are attached to the blade arms 202 and 204 respectively. Each of the wings 226 and 228, and each of the streamline bodies 230 and 232 are integral with each other respectively. The streamline bodies 230 and 232 extend behind the back edges 222 and 224 respectively. Each of the streamline bodies 230 and 232 at least partially fill a space between the wings 226 and 228, and the horizontal plane H. Further, each of the streamline bodies 230 and 232 tapers in a direction opposite to the direction of rotation. Each of bottom surfaces 234 and 236 of the streamline bodies 230 and 232 form a substantially smooth common surface with the blade arms 202 and 204 at end portions 210 and 212 of the blade arms 202 and 204 respectively, radially remote from the rotational axis X.

FIG. 3 illustrates a blade 300 with blade arms 302 and 304 having front edges 314 and 316, and back edges 322 and 324 respectively. The front cutting edges 314 and 316 are substantially straight. Cutting edges 318 and 320 extends partially along the length of the front edges 314 and 316 respectively. Further, each of the blade arms 302 and 304 includes wings 326 and 328 which are upturned for improved collection of cut vegetation. Shape of the wings 326 and 328 results in a space between each of the wings 326 and 328, and the horizontal plane H. A part of each of the back edges 322 and 324 at the location of the wings 326 and 328 extends behind another part of each of the back edges 322 and 324 located at end portions 306 and 308 of the blade arms 302 and 304 respectively, radially closest to the rotational axis X. Moreover, as illustrated in FIG. 3, streamline bodies 330 and 332, which are attached to the blade arms 302 and 304, extend behind the back edges 322 and 324 respectively. Each of the streamline bodies 330 and 332 at least partially fills the space between the wings 326 and 328, and the horizontal plane H. Further, each of the streamline bodies 330 and 332 tapers in a direction opposite to the direction of rotation. Each of bottom surfaces 334 and 336 of the streamline bodies 330 and 332 form a substantially smooth common surface with the blade arms 302 and 304 at end portions 312 and 314 of the blade arms 302 and 304 respectively, radially remote from the rotational axis X.

In the drawings and specification, there have been disclosed preferred embodiments and examples of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation, the scope of the invention being set forth in the following claims.