JP2632482B2 - Lawn mower blades - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blade that is driven to rotate horizontally in a cutter housing of a lawn mower and that cuts lawn with blades at both ends.

[0002]

2. Description of the Prior Art The blades of such lawn mowers are usually constructed, for example, as shown in U.S. Pat. No. 4,617,788.
It has an elongated rectangular shape, and its center is fixed to a vertical rotation axis, and driven by the rotation axis. The inclined edge portions are formed at the front edges in the rotation direction at both outer ends, and the blades are used to cut grass. The leading edge of this blade is linear from the outer end portion where the blade portion is provided to the main body portion where the blade portion is not provided. In the patent, a triangular notch is provided near the outer end of the blade, and the notch is used to shred leaves and the like mixed in the grass.

[0003]

In the blade as described above, the blade portion may collide with foreign matters such as pebbles during mowing. By the way, since this blade is polished at the front edge of the plate-like body at an angle, the front edge is sloping, and at the boundary between the slashed portion and the unsharped portion inside, The cross-sectional shape of the leading edge changes rapidly. Therefore, when a large force acts on the blade portion due to collision with foreign matter, stress concentrates on the above-mentioned boundary portion, and large stress is easily generated here. In addition, a notch phenomenon easily occurs in the triangular notch.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and according to the present invention, it is mounted on a vertical rotating shaft projecting into a cutter housing, and is mounted on the vertical rotating shaft. In the blade of the lawn mower, which extends elongated on both sides in the diameter direction and has a blade portion at each of the rotation direction front edges at both ends, the rotation direction front edge has a connection portion between the inner end of the blade portion and the blade body portion, An arc-shaped concave portion is provided which is recessed from the leading edge, and the radius of curvature of the arc is set to about 20 to 60 times the thickness of the blade, and the depth of the recess is set in the rotation direction of the blade portion. Make it almost equal to the width.

According to the present invention, since the sharp front edge of the blade portion gradually increases in thickness along the arc shape of the concave portion and transitions to the thickness of the blade body, the blade front edge is moved from the blade portion to the body portion. There is no sudden change in the cross-sectional shape of the recess, and even when viewed in plan, the recess has a very gentle curvature, and is only recessed by the small depth required for the above-mentioned thickness transition. Therefore, stress concentration does not occur in this portion. Further, even if foreign matter collides with the concave portion, the notch phenomenon is relatively unlikely to occur in the concave portion.

As a result of intensive studies, the present inventors have made the radius of curvature of the arc of the recess approximately 20 to 60 times the thickness of the blade, and the depth of the recess substantially equal to the width of the blade in the rotational direction. It has been found that by making them equal, the concentrated stress at the inner end portion of the blade can be appropriately dispersed without impairing the performance and productivity of the blade, and the occurrence of large stress can be effectively prevented.

[0007]

FIG. 1 is an overall perspective view of a lawnmower equipped with a blade according to the present invention. The lawn mower includes a main body 3 movably supported by a pair of left and right front wheels 1 and rear wheels 2, and a steering handle 4 extending rearward from the main body 3.

An engine 5 is mounted on the main body 3, and a cutter housing 6 which is opened downward is provided below the engine 5. A rotating shaft 7 which is an output shaft of the engine 5 projects vertically from above into the cutter housing 6, and a blade 8 is attached to the rotating shaft 7, driven by the engine 5 via the rotating shaft 7, and Rotate horizontally within.

As shown in FIG. 2, the blade 8 has an elongated rectangular plate shape, the center of which is fixed to the rotating shaft 7, and extends horizontally to both sides in the diameter direction of the rotating shaft 7. The blade 8 is driven by the rotating shaft 7 and rotates in the direction of arrow a in the horizontal plane. Blade portions 10 and 10 are formed at the leading ends of the front edges 9 and 9 in the rotating direction, respectively. Reaped.

As shown in FIG. 3 to FIG.
A guide blade 12 is formed at a tip portion corresponding to the blade portion 10 on the front edge 9 side. The guide blade 12 is curved and erected upward. Can be The blade portion connected to the tip portion provided with the blade portion 10 and the guide blade 12 is provided with a concave / convex portion 13 extending in the longitudinal direction at the center in the width direction, thereby increasing the sectional modulus of the portion, The blade 8 is prevented from being deformed by the force acting on the blade 10. The blade 8 is slightly twisted so that the blade portion 10 at the leading edge is lower than the other portions. However, the sectional views in FIG. .

The blade portion 10 is formed by polishing the leading edge of the tip of the blade 8 having a rectangular cross section, for example, so that the upper surface is a slope 10a. Therefore, the leading edge 9 of the blade 8 is composed of a portion 9a provided with the blade portion 10 and a portion 9b on the inner side thereof without a blade portion.
Between the blade 8 and the blade 8 in an arc shape in the width direction.
14 are formed. By interposing the recess 14 between the leading edge portion 9a and the leading edge portion 9b in this manner, the portion 9
a, that is, the triangular cross-sectional shape of the blade portion 10 (FIG. 5) does not suddenly change to the quadrangular cross-sectional shape of the portion 9b (FIG. 7), but gradually changes along the arc 14a defining the recess 14. To go. In other words, an arc 14 with a relatively long leading edge
The thickness of the blade 8 is shifted to the thickness t of the main body of the blade 8 while gradually increasing the thickness along t, t ₁ , t ₂ ... (see FIG. 8).

In the conventional blade, as described above, when a foreign object collides with the blade during a mowing operation and a large force is applied, the bladed portion and the inner portion of the blade are not bladed. A large stress is generated at the boundary with the stress due to stress concentration. However, in the present embodiment, the concave portion 14 as described above is provided at the above-mentioned boundary portion, and there is no portion where the cross-sectional shape changes abruptly at the front edge 9, so that large stress is generated due to stress concentration. Is prevented. That is, this stress is dispersed around.

The stress reducing effect of the recess 14 depends on the curvature of the arc 14a. By selecting the radius of curvature R to be about 20 to 60 times the thickness t of the blade 8, local large stress can be reduced. It can be effectively prevented. This was confirmed by the experiments described below.

The same experiment was repeated for a conventional blade having substantially the same size and shape and a blade according to the present invention in which the radius of curvature R was variously changed, and the stress at the root portion (boundary portion) of the blade portion was measured. did. FIG. 9 is a perspective view of an outer end portion of a conventional blade 15 subjected to an experiment, and FIG. 10 is a similar perspective view of the blade 8 according to the present invention. In each case, the plate thickness t was 2.5 mm, and the width l _{2 of the} blade portion (see FIG. 3) was 3 mm.

In the blade 15, a relief portion C is formed at the base of the blade portion 10, and the front edge 9a of the blade portion 10 gradually increases in thickness and reaches the same thickness as the front edge 9b of the main body portion. However, a strain gauge 16 for measuring stress was attached to a point B where the thickness starts to increase. On the other hand, in the blade 8,
Using the point corresponding to the point B as a reference, the concave portion 14 was formed by allocating the concave portion 14 to both sides thereof, and a strain gauge 17 was attached to the deepest portion.

The radius of curvature R of the concave portion 14 provided on each blade 8
Were set to various sizes of 20, 50, 100, and 150 mm, and the depth of each recess was almost equal to the width l ₂ (= 3 mm) of the blade 10 (see FIG. 11). Therefore through each blade 8 strain gauge
17 is in the same position and the strain gauge on blade 15
Both are at the same radial position, that is, at the same distance from the outer edge of the blade. In FIG. 11, the width l ₂ of the blade portion 10 is exaggerated as compared with each radius of curvature R.

Each blade 15, 8 is fixed at the center, that is, at a position to be mounted on the rotary shaft 7, and a force F of 250 Kgf is applied to the blade portion 10 at a position a (= 1 inch) inside from the outer end.
Was statically applied (FIGS. 9 and 10), and the stress at the portion was measured from the amount of strain detected by the strain gauges 16 and 17. The results are shown in the following table. Blade Stress Blade 15 (conventional type) 31 kg / mm ² or more Blade 8 R = 150 mm 22 kg / mm ² R = 100 mm 24 kg / mm ² R = 50 mm 24 kg / mm ² R = 20 mm 27 kg / mm ²

FIG. 12 is a graph showing the results of the above experiments.
If the thickness is not less than mm, that is, not less than 20 times the thickness of the blade 8 (2.5 mm), the stress is sufficiently dispersed and only a relatively small stress is generated. On the other hand, even when R> 150 mm, the stress is well dispersed, and the stress is rather lower than when R = 150 mm. However, when R is 150 mm or more, the effective length of the blade portion 10 is shortened, The mowing finish is not good, and
In consideration of these points, R should be set to 150 mm, that is, 60 times or less of the blade plate thickness.

Further, in order to prevent local large stress from being generated by the concave portion 14, the concave depth l ₁ of the concave portion 14 is set to be equal to the blade width l _{2 of the} concave portion 10.
It is enough to make it approximately equal to
The cross-sectional area of the blade 8 in this portion is reduced, and the strength and rigidity are reduced.

[0020]

According to the present invention, the stress generated on the blade due to foreign matter colliding with the blade during mowing is relatively effectively prevented from being generated locally. can do. Also, even if foreign matter collides with the concave portion, the notch phenomenon of the concave portion is relatively unlikely to occur.

[Brief description of the drawings]

FIG. 1 is an overall perspective view of a lawnmower equipped with a blade according to the present invention.

FIG. 2 is an overall plan view of a blade.

FIG. 3 is a plan view of a blade tip.

FIG. 4 is a front view of the blade tip viewed from the front in the rotation direction.

FIG. 5 is a sectional view taken along the line VV of FIG. 3;

FIG. 6 is a sectional view taken along the line V1-V1 of FIG. 3;

FIG. 7 is a sectional view taken along line V11-V11 in FIG. 3;

FIG. 8 is an enlarged view of a portion A in FIG. 6;

FIG. 9 is a perspective view of an outer end portion of a conventional blade used for an experiment.

FIG. 10 is a perspective view of an outer end portion of a blade according to the present invention subjected to an experiment.

FIG. 11 is a schematic diagram showing a planar shape of a concave portion of each blade used in an experiment.

FIG. 12 is a graph showing experimental results.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Front wheel, 2 ... Rear wheel, 3 ... Body part, 4 ... Handle, 5 ... Engine, 6 ... Cutter housing, 7 ... Rotating shaft, 8 ... Blade, 9 ... Leading edge, 10 ... Blade part, 11 ... Rear Edge, 12: Guide vane, 13: Uneven portion, 14
... recess, 15 ... blade, 16, 17 ... strain gauge

Claims (1)

(57) [Claims] 1. A lawn mower blade mounted on a vertical rotating shaft protruding into a cutter housing, extending elongated from the rotating shaft on both diametrical sides thereof, and having blades formed at respective rotationally leading edges at both ends. An arc-shaped concave portion recessed from the front edge is provided at a connection portion between the inner end of the blade portion and the blade body portion at a front edge in the rotation direction, and the radius of curvature of the arc is set to the blade plate. A blade for a lawnmower, wherein the blade has a thickness of about 20 to 60 times and a depth of the recess is substantially equal to a width of the blade in the rotation direction.