GB2028089A - Improvements in or relating to cutters for vegetation - Google Patents

Abstract

In order to provide a construction of vegetation cutter of the air cushion supported type which requires a motor of lower power to create a fully effective air cushion support for the motor (9), the cutter has a casing (1) of shallow, dish- shaped form with a depending peripheral rim (5), and an air impeller (10) positioned within the casing. At least that part of the rim adjacent the edge thereof has an internal contour that is inturned slightly (6) with respect to the casing and is such that in use, air from the impeller is deflected downwardly and inwardly of the casing, the rim, at least round the leading and trailing parts thereof having no external extensions. <IMAGE>

Description

SPECIFICATION Improvements in or relating to cutters for vegetation This invention relates to cutters for vegetation and has particular although not exclusive reference to grass cutters and lawn mowers.

It has been proposed to support a grass cutter on a cushion of air and thereby facilitate the use of the cutter on ground over which it is difficult or impossible to use a cutter of a more conventional construction.

The cushion of air may be created by an electrically driven fan or impeller. It is found that the comparatively large volume of air that has to be used to create the cushion requires a motor of relatively high power. It is an object of the present invention to provide a construction which requires a motor of lower power to create a fully effective air cushion support for the motor.

According to the present invention, a vegetation cutter has a casing of shallow, dishshaped form with a depending, rigid peripheral rim, at least that part of the rim adjacent the edge thereof having an internal contour that is inturned slightly with respect to the casing and in such manner that, in use, air impinging upon the inturned contour is deflected inwardly towards the centre of the casing, the rim, at least round the leading and trailing parts thereof, having no externallyextending flange.

The inturned contour may be curved or it may be straight and inclined to the vertical at an angle lying within the range of from 10 to 20*, preferably at an angle of about 15 .

Preferably, the casing has internally-extending flanges at least round leading and trailing surfaces of the rim, the inward extent of such flanges being sufficient merely to prevent the surfaces "digging into" the ground and so impeding easy movement of the cutter over the ground.

In one form, the casing constitutes a plenum chamber in which is counted a centrifugal impeller drawing air from an air inlet in the casing. The effect of the inturned contour of the rim is to create an effective air curtain round the periphery of the casing and this reduces the loss of air from inside the casing and thus contributes to a more easily retained air cushion for supporting the vegetation cutter. Reduction of air loss means that a smaller volume of air has to be drawn into the casing by the impeller and thus a lower power motor may be employed for driving the impeller.

In another form, an axial flow fan is used.

The output of the fan is constrained to follow a path closely adjacent the inner surface of the casing and this may be effected by an inner baffle or shield.

It is found that too sharp an inturned contour adversely affects the stability of the vegetation cutter whilst the effectiveness of the air curtain in retaining the air cushion is reduced if the inturn is not sharp enough.

It will, of course, be appreciated that the external contour of the rim need not follow the internal contour.

The casing and rim may be of one-piece construction and if desired, the inturned flanges may be an integral part of the rim.

The casing, rim and flanges (if present) may be of a plastics material and formed by a moulding process, or they may be formed from metal, for example by a pressing operation.

In another embodiment of the invention, the casing is of two-part construction of which one part-the upper part when the cutter is in use, is of a shallow, dish-like form with a short depending rim, the other, lower part comprising the inturned contour of the rim.

The parts may have interlocking surfaces enabling them to be secured together in a substantially leak-proof manner.

Different materials may be used for the separate parts and these may be differently coloured. A stronger material may be used for the lower part, a material that may be more rigid and with, for example, a greater resistance to impact or abrasion. The parts may be formed from suitable plastics materials by a moulding process. Alternatively, the parts may be of metal and formed, for example, by a pressing operation. Detachability allows the lower part to be replaced if damaged or worn unduly.

Interposed between the parts may be a spacer or spacers on whose presence or absence will depend the height of cut of the vegetation cutter. Of course, height variation may be achieved in other ways, for example by adjusting the vertical position of a cutter assembly relatively to the casing.

The driving motor, which may be an electric motor is contained in a housing mounted upon the outer, upper surface of the casing.

The driving or output shaft of the motor passes downwardly through the casing and supports, within the latter, an impeller and the cutter assembly mentioned above.

Alternatively, the motor may be mounted with a housing formed with the casing as an integral part thereof.

If desired, speed reduction gearing may be interposed in the drive from the motor to the impeller and cutter and, in another embodiment of the invention, the impeller is formed or provided with gear teeth which mesh with a pinion driven by the motor and which could, for example, be mounted upon the output shaft of the motor. The impeller may have an internal or external ring gear that meshes with the pinion. The impeller and gear may be made as a one-piece moulding in a suitable plastics material for example nylon or polypropylene. The internal or external gear may be a preformed metal component secured to the impeller by any suitable process. Alternatively, a belt drive could be used to transmit drive from the motor to the impeller. The driving belt may be a toothed belt and may be of a plastics material, for example, nylon to reduce the emission of noise.

The cutter may be a twin or multi-bladed metallic cutter, or it may be a filament, rotated in a horizontal plane by the driving motor. The filament may be contained in a reel and housing unit for example that described in the Specification of co-pending Patent Application No. 45756/77 or it may be of the form described in U.S. Patent Specification No. 3,895,440. Where -a filament is used, the speed or rotation will be appropriate to that form of cutter, and normally a higher speed of rotation then is used as compared with the speed of rotation of a metallic blade -cutter.

By way of example only, embodiments of the invention will now be described in greater detail with reference to the accompanying drawings of which: Figure 1 is a diagrammatic plan view of a first embodiment, Figure 2 is a section on the line Il--Il of Fig.

1, Figure 3 is a section on the line Ill--Ill of Fig. 1, and, Figure 4 is a scrap view on an enlarged scale of part of the first embodiment.

The embodiment shown in Figs. 1 and 2 is suitable for use as a lawn mower and has a casing 1 of shallow, dish-shaped form that is generally rectangular when seen in plan as in Fig. 1 with straight longer sides 2 and rounded shorter ends 3, 4. End 3 is the leading edge and end 4 the trailing edge. The rectangular shape enables the necessary clearance between the end 4 and the ends of a metallic cutter blade mounted within the casing to be obtained more economically than would be the case with a casing of circular form when seen in plan. However, if as will be described later a filament cutter is used and safety regulations permit, the casing could be circular when seen in plan. A circular casing produces a more stable action when the cutter is in use.

As can be seen most clearly from Figs. 2 and 3, the casing 1 has a downturned, depending peripheral rim 5 the lower (as seen in Fig. 2 and 3) part of which is inturned as indicated at 6. At the leading and trailing ends 3, 4, the rim 5 has an inturned horizontal flange 7. The flange is also shown in dotted lines in Fig. 1.

Mounted upon the upper surface of the casing 1 is a housing 8 accommodating an electric motor 9 on whose output shaft is mounted a centrifugal impeller 10 and a cutter blade 11 of conventional form.

Also mounted upon the upper surface of the casing 1 are mounts 1 2 for the ends of an operating handle (not shown) by which a user guides the mower and which also carries the controls for the electric motor.

The inturn 6 is provided in the embodiment shown in Figs. 1, 2 and 3 by inturning the lower part of the rim, the inturn being flat and such that it lies at an angle of 15 to the vertical as shown in more detail in Fig. 4.

That angle is found to produce an effective air curtain for the containment of the air cushion as will be explained below. However, the angle between the tangent and the vertical lies within the range 10"-20" (both limits included).

Alternatively, the inturn 6 may be produced by curving inwardly the lower part of the rim, the curvature being arcuate and such that a tangent to the curve drawn contacting the edge of the lower part lies at an angle to the vertical within the range 10"-20" (both limits included) but preferably 15 .

Beyond the lower end of the range the inturning of the air flow becomes such that the air curtain is ineffective while beyond the upper end the mower tends to become unstable in use and will not easily remain level. The tendency to instability is more pronounced with larger mowers.

The casing 1 may be a one-piece moulding of a plastics material, for example polypropylene but it is found more convenient to form the casing in two parts of which one the upper part-is of shallow dish-like form and the other-the lower part--comprises the inturned part of the rim. The parts are formed with interlocking surface enabling them to be secured together in a substantially air-tight manner.

Where a two-part construction is used, different plastics materials may be used for the two parts which may also be of different colours. A stronger material, for example ABS, may be used for the lower part-a material that provides a more rigid article and a greater resistance to impact and abrasion. Alternatively, the parts may be of metal and be formed by a pressing operation.

Interposed between the parts may be one or more spacers which will determine the height of cut of the mower. Height variation may also be achieved in other ways, for example by adjusting the vertical position of the cutter blade with respect to the casing. Such adjustment can be effected by washers located on the motor output shaft between a shoulder on the latter and the cutter blade.

The housing 8 may also be mounted or pressed integrally with the upper part of the casing or it may be a separate component secured in suitable manner to the casing 1.

In operation, air is drawn into the impeller via a suitable aperture or apertures in the casing and the output thereof follows the internal contour of the casing 1 and is di rected inwardly and downwardly by the inturned part 6 of the rim thereby producing an effective peripheral air curtain which serves to reduce the loss of air from the casing 1 which would otherwise occur. Such reduction enables a driving motor to be used of a lower power than would otherwise be the case.

The mower is operated in the conventional manner by the user mowing it to and fro across an area of grass or other vegetation to be cut. The flanges 7 facilitate such movement particularly over uneven ground because they reduce the possibility of either the leading or trailing ends "digging" into the ground and so impeding easy movement of the mower over the ground.

The inturned part of the rim of the casing may be planar as indicated in Fig. 4. The angle between the planar portion and the vertical is preferably about 15 but may take any other value within the range 10"-20" (both limits included).

It is not essential to use a centrifugal impeller to create the air curtain and the air cushion. An axial flow fan may be used in conjunction with baffle or shield which constrains the output of the axial flow fan to follow a path closely adjacent the inner surface of the casing to create the air curtain.

The cutter blade may be replaced by a flexible filament fed out from a reel detachably secured to the output shaft of the driving motor. The reel may incorporate an automatic feed for the filament which ensures that the cutting length thereof is maintained at an effective value. Alternatively, the reel may incorporate a user operated release that allows the reel to release a given length of filament when the release is operated. A fila ment cutter may be used with a casing of circular form when seen in plan provided safety regulations permit this. The circular casing will, of course, retain the inturned contour referred to above to create the air curtain.

The mower may be adapted to carry a grass box into which cut grass or other vegetation is ejected from the casing.

The grass box is removably mounted upon the casing and may be of annular form to fit round the motor housing described above or the box may be attached to the side or rear of the casing. In each case, the casing is apertured to allow passage of cut grass into the box. Where a cutter blade is used, the blade ends may have extensions contoured to en courage movement of cut grass towards and into the passage and to create a flow of air towards that passage. In addition, the internal baffles may be fitted to urge the cut grass into the box. Such baffles must not, of course interfere with the creation of the air curtain or the air cushion.

Although in the embodiments described above, the cutter or filament is driven directly from the output shaft, speed reduction gearing may be interposed. For example, the impeller may have an internal or external ring gear which mesh with a pinion on the motor output shaft. The impeller may be formed with the ring gear as a one-piece moulding of a plastics material, for example nylon or polypropylene.

Alternatively, a belt drive could be used.

The belt may be of toothed construction and of a plastics material, for example nylon, to reduce the emission of noise.

Claims (14)

1. A vegetation cutter of the air cushion supported type and having a casing of shallow, dish-shaped form with a depending peripheral rim, an air impeller positioned within the casing, at least that part of the rim adjacent the edge thereof having an internal contour that is inturned slightly with respect to the casing and is such that, in use, air from the impeller is deflected downwardly and inwardly of the casing, the rim, at least round the leading and trailing parts thereof having no external extensions.

2. A cutter as claimed in claim 1 in which the inturned contour is straight and inclined to the vertical at an angle lying within the range 10 to 20 (both limits included).

3. A cutter as claimed in claim 1 in which the inturned contour is arcuate in transverse cross-section and of a curvature such that the tangent to the curve drawn contacting the edge of the lower part is inclined to the vertical at an angle lying within the range 10 to 20 (both limits included).

4. A cutter as claimed in claim 2 or 3 in which the angle is 15 .

5. A cutter as claimed in any one of claims 1-4 in which the casing is rectangular when seen in plan, at least the leading and trailing sides of the rectangular having inwardly extending flanges.

6. A cutter as claimed in any one of the preceding claims in which the said part of the rim is a component formed separately from the remainder of the casing.

7. A cutter as claimed in claim 6 in which the said part is detachably secured to the remainder of the casing in an air-tight manner.

8. A cutter as claimed inclaim 7 in which the part and/or the remainder is adapted to receive at least one spacer for adjusting the height of the mower.

9. A cutter as claimed in claim 6, 7 or 8 in which the part is made of a plastics material capable of resisting abrasion and impact.

10. A cutter as claimed in any one of the preceding claims in which the impeller is an axial flow fan and there is, within the casing, means for directing the output of the fan towards the said part of the rim.

11. A cutter as claimed in any one of the preceding claims in which the casing is formed to permit cut vegetation to be discharged from the casing into a vegetation collecting box.

12. A cutter as claimed in any one of the preceding claims and further comprising a vegetation cutter formed by a flexible filament.

13. A vegetation cutter as claimed in claim 1 substantially as herein described.

14. A vegetation cutter substantially as herein described with reference to and as illustrated by Figs. 1, 2 and 3 or Fig. 4 of the accompanying drawings.