WO1988004135A1

WO1988004135A1 - Positive angle lawnmower base plate

Info

Publication number: WO1988004135A1
Application number: PCT/AU1987/000409
Authority: WO
Inventors: Thomas Neilson Skulander
Original assignee: Avantech Pty. Ltd.
Priority date: 1986-12-03
Filing date: 1987-12-02
Publication date: 1988-06-16
Also published as: AU610546B2; AU8339587A

Abstract

A lawnmower (10) of the type having blade means (9) rotatable in a plane substantially parallel to the ground and having a wheeled base plate (11) extending above, and a base plate side wall (12) extending substantially circumferentially around, the blade means (9) which base plate (11) and side wall (12) serve to direct cut grass into grass catching means (15) mounted on the lawnmower, the improvement that the base plate side wall (12), or at least a radially inner cut grass engaging surface thereof, is inclined upwardly and radially inwardly. The inclined side wall (12) acts to lift the cut grass against the underside of the base plate and thus direct it efficiently into the grass catcher (15) at lower blade speeds, and thus with lower noise, than conventional lawn mowers.

Description

"POSITIVE ANGLE LAWNMOWER BASE PLATE"

Technical Field

The present invention relates to an improved motorised lawnmower of the type having blade means rotatable in a plane substantially parallel to the ground and having a wheeled base plate extending above the blade means and a base plate side wall extending substantially circumferentially around the blade means which base plate and side wall serve to direct grass cut by the lawnmower into grass catching means mounted on the base plate.

Background Art

It is well known to provide lawnmowers of the type having blade means rotatable in a plane substantially parallel to the ground with a grass catcher to collect the cut grass discharged from the lawnmower. In order to successfully collect the cut grass, particularly when the grass is wet, it has been necessary to increase the speed of rotation of the blades and to provide an upturned portion on the blades (hereinafter called the "lift angle") to induce the air flow induced by the blades to rise against the base plate and to carry with it the cut grass. This air stream, and the cut grass, are then directed into the grass catcher. The increase in engine speed of such lawnmowers and the extent of the lift angle has caused such grass catching lawnmowers to be very noisy. Noise standards are now being introduced by law which has caused lawnmower manufacturers to lower engine speeds to reduce the noise however this has the disadvantage that grass catching efficiency is reduced particularly under adverse conditions such as wet grass or long and/or thick grass.

Disclosure of the invention

The present inventor has discovered that the grass catching efficiency of lawnmowers of the above type may be significantly improved, even at lower than normal engine speeds, by the use of a novel configuration of the radially inner, cut-grass engaging, surface of at least a part of the side wall surrounding the base plate.

The present invention consists in a lawnmower of the type having blade means rotatable in a plane substantially parallel to the ground by a motor and having a wheeled base plate extending above, and a base plate side wall extending substantially circumferentially around, the blade means, which base plate and side wall serve to direct grass cut by the lawnmower into grass catching means mounted on the lawnmower, the lawnmower being characterized in that the base plate side wall includes a radially inner, cut grass engaging, surface portion which is inclined upwardly and radially outwardly. The blade means preferably comprise a circular blade plate attached at its centre to the vertically aligned spindle of a suitable motor and carrying at its periphery a plurality of blades. In an alternative embodiment of the invention a single elongate blade connected at its mid-point to the motor spindle may be used. The blade, or blades, is, or are, preferably each provided with a lift angle. This lift angle may be smaller and of lower angle than those on conventional grass catching lawnmowers, e.g., conventional, lift angles are raised up out of the plane of the blade by about 50° whereas the blade angle on the blades for the present mower is preferably from 30° to 45°, most preferably 35° to 40°.

The motor for use with the blade means on the lawnmower according to this invention preferably rotates at from 2000-2500 rpm. This is to be compared with conventional lawnmowers which rotate at between 3700-3800 rpm, and the "Vortex" lawnmower (described in Australian Patent Specification No. 515003) designed to be quieter than conventional lawnmowers which rotates at 2800-3000 rpm. The reduction in rotational speed of the motor reduces the noise generated by the motor itself as well as the noise generated by the rotation of the blades. The motor may be of any suitable type however preferred motors include internal combustion engines, more particularly petrol fuelled two-stroke or four-stroke engines, and electric motors.

The grass catcher itself may be of any conventional design however it is in preferred embodiments of this invention mounted at the trailing end of the lawnmower. The base plate and side wall may be formed of any suitable material such as pressed steel, cast aluminium or moulded synthetic plastics materials. It is however an essential feature of the invention that at least part of the radially inner surface of the side wall of the base plate is inclined radially outwardly and upwardly.

Conventional base plates are either vertical or inclined downwardly and outwardly due to the constructional methods used in their manufacture which have in some cases required a draw angle to allow removal of the base plate in one piece from a mould or press. The base plate according to the present invention may be produced in a plurality of parts which are then bolted, welded or otherwise connected together or a suitably shaped shim may be provided on the inside of the base plate of a conventional lawnmower. In a particularly preferred embodiment of the invention, however, the base plate is formed in one piece by reaction injection moulding from a suitable grade of polyurethane. In this method the base plate is removed from a suitable mould in a pliable condition and is placed in a suitable jig which biases the side wall into the correct inclination and allows it to cure and harden in this shape.

The side wall of the base plate is preferably inclined, and therefore has a radially inner surface which is inclined, upwardly and radially outwardly by an angle of from.7 to 15° to the vertical, most preferably from 10 to 12° to the vertical. The inclinations may extend from the junction of the sidewall and the base plate vertically downwardly only a part of the height of the side wall leaving a vertical skirt at the bottom or it may extend downwardly through the full height of the side wall. The inclined section of the side wall may extend over only a small section of the circumference of the side wall or virtually all the way around the side wall. In particularly preferred embodiments of the invention the side wall is inclined over an arc of at least 90° and most preferably at least 225° terminating in an outlet chute for the cut grass which chute is in communication with the grass catching means on the base plate. It is believed that the inclination of the side wall induces the cut grass to rise up the side wall until it is travelling adjacent the undersurface of the base plate due to the centrifugal force applied to the grass by the cutting action of the blade. This clears the grass from the cutting path of the blade and simultaneously lifts it into a clear stream of flowing air which is carried out from beneath the base plate along the chute into the grass catcher where the flow velocity of the air drops and the grass settles out. While this is believed to be the action induced by the inclined side wall of the base plate the applicant is not limited to this explanation.

It is preferred that the base plate is formed with an arcuate portion immediately adjacent the side wall which gradually increases in height above the ground as it approaches the outlet chute. This arcuate portion increases the enclosed space of the base late on the side adjacent the outlet chute as compared with the other side of the base plate volume. In preferred embodiments of the invention the enclosed base plate volume on the side adjacent the chute is from 1 to 1.5 times the volume enclosed by the other side of the base plate. Brief Description of the Drawings

Fig. 1 is a plan view of a lawnmower according to the present invention; Fig. 2 is a radial sectional view along section line A of Fig. 1;

Fig. 3 is a radial sectional view along section line B of Fig. 1;

Fig. 4 is a radial sectional view along section line C of Fig. 1;

Fig. 5 is a radial sectional view along section line D of Fig. 1;

Fig. 6 is a radial sectional view along section line E of Fig. 1; and Fig. 7 is an underneath plan view of the lawnmower of Fig. 1. Best Mode of Carrying out the Invention

Hereinafter given is a preferred embodiment of the present invention described with reference to the abovementioned drawings.

The lawnmower 10 includes a base plate 11 having a generally downwardly extending side wall 12; four wheels 13; a motor 14 mounted on top of, and substantially centrally on, the base plate 11; a blade plate and blades blades 9 mounted on the spindle of the motor 14; and a grass catcher 15 mounted on the back of the base plate 11. The lawnmower 10 would normally include a handle on which are mounted engine controls however for the sake of clarity the handle has been omitted from the present drawings.

As is best seen in the sectional drawings. Figs. 2 to 6, from which the engine, wheels and the like have been omitted for greater clarity, the side wall 12 of the base plate 11 is substantially vertical on section line E. As the side wall 11 progresses around the periphery of the base plate 11 it starts to be inclined upwardly and outwardly. At this point also a radially outer portion 16 of the base plate 11 begins to be raised up to form a downwardly opening trough 17. At section B the angle of the side wall 12 has steepened and the width and depth of the trough 17 increased. At section C the side wall 12 angle has remained unchanged however the lowermost portion of the side wall is vertical, the trough 17 has substantially increased in depth but has become narrower. At the section D, immediately before the trough 17 forms a chute 18 discharging into the grass catcher 15, the side wall 12 angle has remained unchanged though the lowermost vertical section has become deeper.

The base plate 11 and side wall 12 are formed integrally be reaction injection moulding of polyurethane. The motor 14 is a petrol fuelled four-stroke engine rotating at 2200 rpm in normal usage.

The configuration of the base plate 11 and side wall 12 was found to direct the cut grass efficiently into the grass catcher even under adverse conditions such as when the grass is wet. The grass clippings appeared to be raised up against the underside of the base plate 11 by the upwardly and outwardly inclined side wall 12 and the centrifugal force applied to the grass by the blade assembly 9. The increased depth of the trough 17 adjacent the chute 18 ensures that the grass enters the grass catcher 15 near its top thereby preventing the chute from becoming choked up before the grass catcher 15 is filled.

Claims

CLAIMS : -

1. A lawnmower of the type having blade means rotatable in a plane substantially parallel to the ground by a motor and having a wheeled base plate extending above, and a base plate side wall extending substantially circumferentially around, the blade means, which base plate and side wall serve to direct grass cut by the lawnmower into grass catching means mounted on the lawnmower, the lawnmower being characterized in that the base plate side wall includes a radially inner, cut grass engaging, surface portion which is inclined upwardly and radially outwardly.

2. A lawnmower as claimed in claim 1 in which the inclination of the side wall is at an angle of from 7 to 15° to the vertical.

3. A lawnmower as claimed in claim 2 in which the inclination of the side wall is at an angle of from 10 to 12° to the vertical.

4. A lawnmower as claimed in any one of claims 1 to 3 in which the inclined portion of the side wall terminates at an outlet chute for the cut grass which is in communication with the grass catcher.

5. A lawnmower as claimed in any one of claims 1 to 4 in which the inclined portion of the side wall extends through an arc of at least 90°.

6. A lawnmower as claimed in claim 5 in which the inclined portion of the side wall extends through an arc of at least 225°.

7. A lawnmower as claimed in claim 4 in which the base plate is formed with an arcuate portion immediately adjacent the side wall which increases in height above the ground as it approaches the chute.

8. A lawnmower as claimed in claim 7 in which the volume enclosed by a half of the base plate terminating at the chute is from 1 to 1.5 times the volume enclosed by the other half of the base plate.

9. A lawnmower as claimed in any one of claims 1 to 7 in which the blade means includes at least one blade having a lift angle of from 30 to 45°.

10. A lawnmower as claimed in any one of claims 1 to 9 in which the motor rotates the blade means at from 2000 to 2500 rpm.