GB1576983A - Lawn mower - Google Patents

Description

(54) LAWN MOWER (71) We, FLYMO S.A., a Swiss body corporate, of Altenstrasse 12, CH 6301 Zug, Switzerland) do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a lawn mower of the type which during operation is supported by an air cushion, and comprises a rotary blade driven by an electric or internal combustion motor and rotatable about a vertical axis, and a fan rotatable about the same axis, the blade and the fan being shrouded by a hood.

Lawn mowers of this type are well known, see for instance British patent specification No. 929,610. Such a mower can suffer from problems of vibration due to the transfer of out-of-balance forces from the fan and/or blade through the spokes of a motor mounting platform which is located centrally at the top of the hood. The spokes which lie in a horizontal plane, are narrow in vertical extent, and as a result suffer from lack of stiffness. Because the out-of-balance forces lie below the horizontal plane they can cause bending of the spokes which can in turn cause vanes of the fan to strike the underside of the hood, which is highly undesirable.

The invention aims to solve this problem by reducing the effects of the out-of-balance forces. According to this invention, in a mower of the type referred to, the hood carries means which support the motor so that the lower end of the motor is below the level of the top of the hood, the said means providing an opening or openings for passage of air into the hood for the air cushion. Thus, if the said means are in the form of radiating spokes, they can constitute the sides of an inverted frusto-cone, so forming a stiffer arrangement, since a proportion of the forces are transmitted longitudinally along the spokes into the hood. The effect is also to reduce the distance between a motor mounting platform and the location of the out-ofbalance forces, so reducing their effect.

The invention will now be described by way of example, with reference to the drawing, in which: Fig. 1 is a longitudinal section through a mower in accordance with the invention; and Fig. 2 is a plan drawn to an enlarged scale of a motor-carrying insert.

Referring to the drawing, an air cushion type mower has a hood 10 with a central insert 11 having an inverted frusto-conical part 12. The latter has openings 13 through which air is sucked by a fan 14 to form the air cushion. The part 12 is integral with an inner disc 15 having a central hole 16, through which cooling air for an electric motor 18 can be drawn and through which a vertical shaft 17 of the motor rotates. The motor is fastened to the inner disc 15 by screws (not shown) which locate through holes 19. The shaft 17 at its lower end supports the fan wheel 14 and a rotary blade 20. The fan is a two-stage impeller, and the central part of the fan draws cooling air through the motor 18, whereas the peripheral part of the fan 14 draws air through the openings 13 to form the air cushion below the hood.

In a mower driven by an electric motor, the motor is shrouded by a cover 21 with an upper part 22 forming a chamber 23 with inlet openings 24 for entry of cooling air for the motor. The cover 21 is mounted slightly above the hood by means of fasteners 25 leaving a gap for air to enter the openings 13.

The mower has a handle 26.

In a mower (not shown) driven by a petrol engine, the air supply simply passes through the openings 13.

The mower operates in the following manner.

When the motor 18 rotates the fan and blade, the peripheral part of the fan forces air into the hood to form the air cushion and the mower will hover above the ground while the blade 20 cuts the grass. Cooling air is sucked through the motor by the central part of the fan. This cooling air enters the chamber 23 through the inlet openings 24 and continues through the motor.

As can be seen in Fig. 1, the arrangement has the advantage that the centre of gravity of the motor is lower and the plane of the motor mounting platform is nearer to the site of the out-of-balance forces than in known air cushion mowers. This means that the stability of the mower is increased so that the requirement for precise balancing of the rotating components can be somewhat reduced.

WHAT WE CLAIM IS: 1. A mower of the type referred to, wherein the hood carries means which support the motor so that the lower end of the motor is below the level of the top of the hood, the said means providing an opening or openings for passage of air into the hood for the air cushion.

2. A mower according to claim 1 wherein the said means comprises radial spokes.

3. A mower according to claim 1 wherein the said means comprises radial spokes and a central platform on which the motor is mounted.

4. A mower according to claim 2 or claim 3 wherein the spokes form part of an inverted frusto-cone, the upper, outer ends of the spokes being connected to the hood.

5. A mower according to claim 1 wherein the said means is integral with the hood.

6. A mower of the type referred to and constructed and arranged substantially as herein described and shown in the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. mower will hover above the ground while the blade 20 cuts the grass. Cooling air is sucked through the motor by the central part of the fan. This cooling air enters the chamber 23 through the inlet openings 24 and continues through the motor. As can be seen in Fig. 1, the arrangement has the advantage that the centre of gravity of the motor is lower and the plane of the motor mounting platform is nearer to the site of the out-of-balance forces than in known air cushion mowers. This means that the stability of the mower is increased so that the requirement for precise balancing of the rotating components can be somewhat reduced. WHAT WE CLAIM IS:

1. A mower of the type referred to, wherein the hood carries means which support the motor so that the lower end of the motor is below the level of the top of the hood, the said means providing an opening or openings for passage of air into the hood for the air cushion.

2. A mower according to claim 1 wherein the said means comprises radial spokes.

3. A mower according to claim 1 wherein the said means comprises radial spokes and a central platform on which the motor is mounted.

4. A mower according to claim 2 or claim 3 wherein the spokes form part of an inverted frusto-cone, the upper, outer ends of the spokes being connected to the hood.

5. A mower according to claim 1 wherein the said means is integral with the hood.

6. A mower of the type referred to and constructed and arranged substantially as herein described and shown in the drawings.