GB2101864A

GB2101864A - Lawn mower grass collection indicator

Info

Publication number: GB2101864A
Application number: GB08216907A
Authority: GB
Inventors: Daniel Bryan Payen
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-06-11
Filing date: 1982-06-10
Publication date: 1983-01-26
Also published as: GB2101864B

Abstract

A lawn mower is provided with an air float (19) which is supported by a pressure difference between the interior and exterior of the grass box (17). The pressure difference drops if the path to the grass box is blocked e.g. if the grass box is full, and the float (19) falls under its own weight to indicate that grass cannot be successfully collected. In an alternative embodiment, the float is replaced by a thin, flexible membrane. <IMAGE>

Description

SPECIFICATION Improvements in or relating to lawn mowers This invention relates to lawn mowers, and in particularto rotary grass mowers which have a box for collecting grass cuttings.

In rotary mowers which cut and collect the grass the horizontal cutting blade is twisted like a propeller to create a suction. This lifts the cut grass and blows it into the grass box which is attached to the rear of the casing. The grass box is not open and is usually made of tough opaque plastic. There is therefore no means of knowing when it is full. In consequence it is all too easy to go on cutting grass when the box is full. At first this leaves unsightly cutting deposits along-the path of the mower. However it soon leads to clogging of the cutting cavity and subsequent stalling of the motor. Practice is to empty the grass box too often to avoid these effects. Not only in this method tedious but it is uncertain as the rate of grass box filling- is dependent upon the length of grass to be cut.

Rotary mowers are able to cut wet grass. Unfortunately with wet grass the grass outlet throat can clog more easily causing the motor to stall whether the grass box is full or not.

According to the present invention a lawn mower includes an airfloat arranged to be supported buy a pressure difference between grass box interior and exterior.

The float provides an indication of a full grass box or clogged throat since under these conditions the pressure difference set up by rotation of the cutting blade collapses.

Preferably the float is situated in a cut-out in the grass box and is constrained against excessive movement by abutting faces. Alternatively the float may be situated in a fixed vessel. A plurality of floats may be advantageously employed, such as for example pith balls in a tube.

Preferably the float is visible from the exterior of the grass box to provide a direct indication. Alternatively the float may form a concealed sensor, arranged, for example, to activate an electrical connection.

A lawn mower in accordance with the present invention is shown by way of example in the accompanying drawings. An air float is mounted in the grassbox and has a flange at each end to stop it from blowing out or dropping into the box. When the box is not full and the lower throat clear, atmospheric pressure acts on the top of the float whilst the slightly higher pressure inside the box, caused by the vacuum cleaner effect of the cutting blade, acts on the bottom of the float. The differential pressure, therefore, lifts the float giving an indication that the mower is operating correctly. When the box is almost full and the weight of grass is pressing against the mower throat the pressure inside the box falls and the float drops under its own weight.

Provided the mower can lift the float at the start (ie grass box empty), the heavier the float the more sensitive it is to the box nearly full or throat-clogged condition.

The size and weight of the float required is related to the pressure that can be created by the mower.

Low pressure can be compensated by less float weight or larger cross-sectional area.

An embodiment of the present invention has been successfully tested even in grass over 0.3 m long.

The float was constructed from a circular thin walled aluminium tube capped with a thin aluminium plate.

It was about 26 mm in diameter and weighed about 6.5 grams. As an alternative it could be made of a semi-rigid plastic for low cost and more resistance to wear and tear. Assembly may be accomplished by simply pressing the flange through a hole in the grass box.

In order that features and advantages of the present invention may be further appreciated an embodiment will now be described in more detail, by way of example only, with reference to the accompanying diagrammatic drawings of which: Figure 1 represents a part sectional view of a lawn mower in accordance with the present invention, and Figure 2 represents an air float in (a) the lifted position, and (b) the dropped position.

A lawn mower 10 (Figure 1) has a cutting blade 11 rotated by a motor 12 supported by a casing 14 running on front wheel 15 and rear roller 16. The cutting blade 11 is twisted to create an air flow as previously described to carry cut grass toward a grass box 17 via throat 20 and grass outlet 21 along a path, such as path 18. To promote a suitable flow, the grassbox may be vented (not shown).

An air float 19 is mounted in the grass box 17 and is supported bya pressure difference between interior and exterior of the grass box 17. A pressure difference is caused by rotation of the cutting blade 11 and the resultant air flow as previously described.

When the level of grass in the grass box 17 reaches full level 22 or if the pressure difference collapses due to other blockage or clogging of the throat 20 or the outlet 21, air float 19 will no longer be supported but fall to provide an indication that grass can no longer be successfully collected.

Air float 19 has a lower flange 25 (Figure 2a) to retain the float within a circular cut out in grass box 17. The float is supported by air pressure acting on lower surface 26 to provide an indication that the lawn mower is operating normally. An optional transparent cover 27 may be mounted on the grass box exterior to protect the float 19.

In the dropped position, air float 19 is retained in grass box 17 by an upper flange 28 (Figure 2b). In operation, this position indicates that grass cannot be successfully transferred to the grass box 17. This position is also the normal position when the motor is at rest. It will be appreciated that the float upper surface and upper flange 28 preserve the contour of the grass box exterior so that the air float 19 is not vulnerable to damage as the grass box is emptied.

In the embodiment described above, the air float is supported against its own weight acting vertically. It will be realized that many other forms of the present invention are practicable, including supporting the air float against the action of a spring.

In another embodiment represented by Figure 3 of the accompanying diagrammatic drawings of which: Figure 3a represents a section view of a thin container incorporating the float which in this case is a thin loose or flexible membrane supported around its periphery. Figure 3b is a possible view the operator sees when the membrane float is in the lifted position.

Athin container having a translucent cover 30 is attached to the grass box 17. The container is vented to atmosphere above the membrane level. When the membrane float is lifted by the pressure in the grass box 25 so that it makes close contact with the inside of the translucent cover an 'OK' marking (or coloured area) on the membrane becomes clearly visibie to the eye of the operator 28 (see Figure 3b).

As above, Para. 20, Page 3, when the pressure in the grass box falls orthere is a blockage, the membrane float which is suitably weighted, falls away into the dropped position 31 causing the 'OK' marking to become invisible when viewed through the translucent cover.

Claims

CLAIMS The matter for which the applicant seeks protection is:

1. A lawn mower including an air float arranged to be supported by a pressure difference between grass box interior and exterior.

2. A lawn mower as claimed in claim 1 and wherein the air float is visible from the exterior to provide a direct indication of mower operation.

3. A lawn mower as claimed in claim 1 or claim 2 wherein the air float is supported against its own weight.

4. A lawn mower as claimed in claim 1, claim 2 or claim 3 and wherein the air float is substantially as heavy as the heaviest float that can be supported.

5. An air float for use in a lawn mower as claimed in any preceding claim.

6. An air float as claimed in claim 5 and having a central cylindrical portion and abutments to retain the float against excessive movement.

7. An air float as claimed in claim 5 consisting of a loose orflexible membrane fixed around the periphery contained in a thin container, attached to the grass box, the container having a translucent cover.