GB2297889A

GB2297889A - Air cushion lawnmowers

Info

Publication number: GB2297889A
Application number: GB9603586A
Authority: GB
Inventors: Christopher Mark Jordan; Ian Michael Timmins
Original assignee: ATCO QUALCAST Ltd
Current assignee: ATCO QUALCAST Ltd
Priority date: 1995-02-20
Filing date: 1996-02-20
Publication date: 1996-08-21
Anticipated expiration: 2016-02-20
Also published as: GB2297889B; GB9503259D0; GB9603586D0

Abstract

A rotary cushion lawnmower includes a motor 10 driving a cutter 11 for rotation about a substantially vertical axis within a plenum chamber 13. A forced air circulation device 12 in the plenum chamber is rotated about the same axis to produce a flow of pressurised air out of the chamber and into a grass collector 64 disposed within an airtight enclosure remote from the chamber. The flow of pressurised air passes through the grass collector and contributes to an air cushion supporting the enclosure.

Description

AIR CUSHION LAWNMOWERS This invention relates to a powered rotary lawnmower of the type which is supported on a cushion of air and is commonly known as a hovermower.

Such a lawnmower typically comprises a cutter and a compressor fan driven by a motor for rotation about a common vertical axis beneath a protective housing, the compressor fan producing a cushion of pressurised air to support the housing clear of the ground.

A longstanding problem with machines of this type is that collection of the cuttings produced by the cutter is generally unsatisfactory. Attempts to overcome this problem have included using the suction side of the compressor fan to pick up the grass cuttings, and the use of an auxiliary suction fan to boost grass collection.

It has also been proposed to provide a grass collector communicating with the main plenum chamber containing the pressurised air forming the air cushion, and using upturned edges of the rotating cutter blade to impel grass cuttings from the plenum chamber into the grass collector. Such an arrangement is described, for example, in British Patent 2,017,475.

In this case the grass collector may comprise a perforated bag to allow a flow of air through the bag, but such arrangements have the major disadvantage that increasing the flow of air through the grass bag to achieve better grass collection inevitably reduces the amount of air available to form the air cushion and therefore leads to poorer hover performance.

According to the present invention, there is provided a rotary air cushion lawnmower wherein a motor drives a cutter for rotation about a substantially vertical axis within a plenum chamber, and wherein a forced air circulation device in the plenum chamber is rotated about the same axis to produce a flow of pressurised air out of the chamber and into a grass collector disposed within an airtight enclosure remote from the chamber, the flow of pressurised air passing through the grass collector and contributing to an air cushion supporting the enclosure.

Preferably the grass collector is disposed in a rear portion of the airtight enclosure, and the motor is disposed in a front portion of the enclosure, the front portion being supported on a cushion of pressurised air in the plenum chamber.

By way of example only, an air cushion mower embodying the invention is illustrated in the accompanying drawings in which: Fig. 1 is an isometric view of the mower; Fig. 2 is a side elevation of the mower with internal components shown in dashed outline; and Fig. 3 is a plan view with the motor removed.

Referring to these figures, the mower comprises an airtight enclosure 50 formed in two parts, the upper part 51 being secured to the lower part 57 by self-tapping screws 58.

A front portion 52 of the enclosure 50 houses a motor 10 driving a cutter blade 11 and a fan wheel 12 about a common generally vertical axis. The cutter blade 11 and the fan 12 rotate within a circular housing 72 disposed within a plenum chamber 13, and the motor 10 is supported above the plenum chamber within a circular opening 17 in the roof of the chamber.

Rotation of the fan wheel 12 draws air (arrows 'A') into the plenum chamber 13 through an inlet 53 in the front portion 52 of the enclosure, the air entering the chamber through the circular opening 17 in the roof of the plenum chamber. The main air flow is drawn directly through the opening 17 but additional cooling air is drawn over the motor 10 before merging with the main flow.

Air discharged from the fan wheel 12 produces an air cushion in the plenum chamber 13 to support the front portion of the enclosure 50 as it is manoeuvred over the ground using a handle 71. Some of the pressurised air initially produced by the fan within the cutter housing 72 passes under the wall of the housing, and/or through an opening or openings in the wall, to fill the remainder of the plenum chamber 13. A proportion of the pressurised air escapes from the chamber 13 (arrows 'D') beneath an upturned peripheral rim 25.

The fan wheel 12 together with upturned end portions 26 of the cutter blade 11 also produce a flow of air and grass cuttings (arrow 'B') out of the housing 72 and through a volute passage 59. The volute 59 terminates in an exit port 21 provided in a bulkhead 60 which separates the front and rear portions of the enclosure 50. The bulkhead 60 is formed in two mating sections, the upper section being integral with the upper part 51 of the enclosure 50 and the lower section being integral with the lower part 57 of the enclosure. The bulkhead therefore separates the unpressurised upper front portion 52 of the enclosure 50 from the pressurised rear portion 54 of the enclosure.

A grassbox 56 is supported within the rear portion 54 of the enclosure 50 on a crossbar 61. The grassbox is open at the front to receive grass cuttings ejected through the exit port 21 of the volute 59, and it includes permeable walls 63, 64, 66 at the top, sides and rear of the box through which air but not grass is able to pass.

The grassbox therefore filters out the grass cuttings in the air flow (arrow 'C') from the volute 59, and the filtered pressurised air flows into the space 65 between the top wall 63 of the grassbox and the underside of a lid 55 of the enclosure 50 to provide lift to the rear portion 54 of the enclosure (arrows 'E'). The pressurised air also flows into the space between the rear wall 66 of the grassbox and the rear wall 67 of the enclosure 50, and into the space between the side walls 64 of the grassbox and the respective side walls 68 of the enclosure before being discharged beneath the upturned peripheral rim 25 of the enclosure as shown by arrows 'F'.

The lid 55 is hinged and sprung at the rear and held down at the front by a latch 70.

A rubber seal ensures that the lid is airtight. To remove the grassbox for emptying, the latch 70 is released and the grassbox is lifted out of the enclosure using a handle 73.

The bulkhead 60 has the additional advantage that it can be configured to provide the correct airflow balance between grass collection and hover performance. For example, the bulkhead may include bleed holes, and/or the bottom edge of the bulkhead may be raised or lowered to achieve the required balance. The bottom edge may also include a forwardly projecting upturned flange 62, the forward extent of the flange being varied to achieve the required balance.

The illustrated mower has the advantage that grass is thrown directly into the grassbox without being deposited on the ground, and grass collection is therefore achieved without having to mow in straight lines.

Claims

1. A rotary air cushion lawnmower wherein a motor drives a cutter for rotation about a generally vertical axis within a plenum chamber, and wherein a forced air circulation device in the plenum chamber is rotated about the said axis to produce a flow of pressurised air out of the chamber and into a grass collector disposed within an airtight enclosure remote from the chamber, the flow of pressurised air passing through the grass collector and contributing to an air cushion supporting the enclosure.

2. A lawnmower according to claim 1 in which the grass collector is disposed in a first portion of the airtight enclosure and the motor is disposed in a second portion of the enclosure, the second portion being supported on a cushion of pressurised air in the plenum chamber.

3. A lawnmower according to claim 2 wherein the respective first and second portions of the enclosure are separated by a partition, the partition including an opening through which the pressurised air flows into the grass collector.

4. A lawnmower according to claim 2 or claim 3 in which the second portion of the enclosure includes an air inlet through which air is drawn into the enclosure above the plenum chamber.

5. A lawnmower according to claim 4 in which the second portion of the enclosure above the plenum chamber is unpressurised, and the partition further separates the unpressurised portion of the enclosure from the pressurised first portion of the enclosure containing the grass collector.

6. A lawnmower according to any one of the claims 2-5 in which the first portion is at the rear of the second portion.

7. A lawnmower according to any one of the claims 2-6 in which the pressurised air is forced by the air circulation device around a spiral passage extending from the plenum chamber to the grass collector.

8. A lawnmower according to any one of the preceding claims in which the grass collector includes a permeable top wall spaced below the top of the enclosure to provide a gap for the flow of pressurised air providing the air cushion.

9. A lawnmower according to claim 8 in which the rear and/or sides of the enclosure is/are spaced from respective permeable rear/side walls of the grass collector to provide a passage for the flow of pressurised air out of the enclosure.

10. A lawnmower according to claim 1 and substantially as herein described with reference to the accompanying drawings.