GB2282949A - Rotary cutter blade - Google Patents

Abstract

A rotary blade locking device comprises a rotatable drive line 1, a rotatable drive member 8 including a plurality of ramped projections 7, a rotary blade 2 attachable to the driving member for rotary movement therewith, and including at least one additional projection 9 which extends outwardly from the blade and which, when the blade is attached to the driving member is engageable with at least one of the ramped projections. The blade 2 and drive member 8 are locked for rotation by a central bolt. The engagement of the projection 9 and ramped projection 7 prevents relative angular displacement between blade and drive member in a direction which tends to loosen the bolt. <IMAGE>

Description

ROTARY BLADE LOCKING ARRANGEMENT The present invention relates to rotary cutter blades and their attachment to a driving member. In particular, the present invention relates to the attachment of rotary cutter blades to a driving member of a rotary mower supported on a cushion of air or a combination of wheels and rollers.

Although specific reference will be made in this specification to the application of the present invention to rotary members, the underlying concept is applicable to other machines including rotatable cuter blades such as trimmers and saws.

Rotary mowers are well known and normally comprise a hood within which a horizontal cutter blade is mounted for rotation. Rotary mowers are usually supported by wheels or by a cushion of air created by an impeller mounted within the hood, and rotatable with the cutter blade. The cutter blade is normally attached to the impeller or to a driving member which extends through the hood from an electric motor or an internal combustion engine and usually, the driving member in the output shaft of the motor or engine. Typically a bolt attaches the cutter blade to the output shaft or to the impeller. The blade is often held against the output shaft or impeller by friction. In this situation, if during use the rotating blade impacts upon an object, the blade may not only be angularly displaced with respect to the drive line or impeller but also be severely damaged. However since the blade is designed to be angularly displaced in a direction which will tighten the bolt it will not loosen on impact.

Rotary mowers usually have a single blade which is mounted to rotate about the mounting bolt at its centre of gravity.

In certain rotary mowers, the blade is also supported by projections which extend from the driving member or the impeller to prevent angular displacement of the blade with respect to the driving member or the impeller. However, if, in operation, the blades hit a heavy object such as a stone, the projections have been known to break but, as mentioned above impact of the blade normally tightens the bolt.

In either of the two situations, mentioned above, when the mower is turned off, the blade continues rotating for a time due to the inertia built up in the blade and other rotatable parts. In some situations, the motor may act as a brake in which case the torsional force in a drive line connected to the driving member is opposite in direction to that which occurs while the mower is under motive power. This opposite force causes the blade to act on the bolt in a direction which tends to loosen the bolt. Thus, if the bolt holding the blade onto the drive line or impeller is undone, the mower becomes extremely dangerous in that a detached blade may cause great personal injury or damage.

For safety reasons, it is desirable for the blade to reach stand still as soon as possible after the power is turned off since injuries have occurred where the blade has still been moving when a user has inverted the mower for inspection and cleaning. To stop the blade quickly, it is necessary to brake them. The greater the braking force, the more likely it is that the blade will be loosened as stated above.

An object of the invention is to overcome, or at least reduce some of the abovementioned disadvantages and problems.

According to the present invention a rotary blade locking device comprises a rotatable driving member having a plurality of ramped projections; a rotatable blade attachable to the driving member for rotary movement therewith, and including at least one additional projection which extends outwardly from the blade and which, when the blade is attached to the driving member is engageable with at least one of the ramped projections.

Conveniently, the ramped projections are disposed concentrically around the axis of rotation of the drive line and each ramped projection comprises a sloping portion and a stepped portion in the manner of a dog-tooth. In operation the tab is moveable over the sloped portion, but abuts against the stepped portion. Alternatively, each ramped projection may comprise two sloping portions of differing slope in the manner of a saw tooth or a truncatefd saw tooth.

According to one embodiment of the invention, the end of the drive line is an impeller from which the ramped projections extend and the rotary blade is attachable to the impeller by, for example, a bolt.

Preferably, the engagement of the tab and the ramps prevents relative angular displacement between the blade and the drive line or the impeller in a direction which tends to loosen the bolt.

According to another embodiment of the invention, the locking device further comprises a lug extending from the blade, and a series of radial webs extending from the end of the drive line or impeller wherein the lug is engageable with the webs for restricting relative angular displacement of the blade with respect to the drive line or impeller. The webs may be fractured by the lug if movement of the blades is obstructed.

Where the cutter blade of a lawn mower is made from a single piece of metal, sometimes called a bar blade, the inherent spring characteristic of the blade enables the blade to deflect over the ramps if an obstruction is hit whilst maintaining drive in normal cutting conditions. It will, therefore, be appreciated that the inventive concept affords both drive and blade locking under stopping conditions without the aid of any additional components.

Embodiments of the inventions are hereinafter described by way of example, only with reference to the drawings in which: Figure 1 shows a method of fixing the blade rigidly to the motor shaft, according to the prior art; Figure 2 shows an arrangement for attaching the blade to the motor shaft according to the present inventions; Figure 3 shows an arrangement according to the present invention for attaching the blade to a fan wheel which is mounted on a motor shaft, and Figure 4 shows another embodiment according to the present invention for attaching the blade to a fan wheel.

Figure 1 shows a conventional method of fixing a cutter blade (2) to motor shaft (1). In that conventional method, an impeller (3) is fixed onto the end of the motor shaft (1) for rotation therewith, by conventional means, such as a spline connection.

The cutter blade (2) is attached to the impeller (3) by a bolt (4) which passes through the blade (2), through the impeller (3) and screws into the shaft (1).

The cutter blade (2) has two pegs (5) which project from the top surface of the cutter blade (2) for engagement with corresponding detents (6) formed in the impeller. The pegs (5) and detents (6) inter-engage so that the cutter blade (2) is securely located against the impeller (3), and is unable to be angularly displaced with respect to the impeller (3).

This conventional method of fixing the cutter blade (2) to the motor shaft (1) does have some disadvantages. For example, if during use, the cutter blade (2) collides with a heavy object such as a stone or the mower is being used to cut very long grass and stalls it has been known for the pegs (5) to shear, reducing the rotational support of the cutter blade (2) and thereby allowing the cutter blade (2) to be angularly displaced with respect to the impeller (3). If in this condition, the cutter blade (2) subsequently collides with another object, the cutter blade (2) will be angularly displaced in a direction which tightens the bolt (4).

In some circumstances, the cutter blade (2) will be angularly displaced in the opposite direction, thereby loosening the bolt (4). When the operator of a mower removes the power to the cutter blades (2), the inertia built up in the cutter blade (2) during use serves to make the cutter blade (2) continue rotating for a run-down period after the power has been cut off. In some mowers the motor acts as a brake to slow the cutter blade (2). In other mowers, brakes are applied to stop the cutter blades (2) from rotating within a very short run-down period. For reasons of safety, it is advantageous to make the cutter blade (2) stop rotating in the shortest possible period after power has been disengaged.

This braking effect is usually applied to the motor shaft (1) which constitutes a drive line and causes the securing bolt (4) to loosen if no peg (5) detent (6) arrangement exists to prevent angular displacement between the cutter blade (2) and the drive line (1). Loosening of the bolt (4) could lead to the blade (2) flying off the motor shaft (1) during use with potentially serious consequences.

Referring to Figure 2 a motor shaft (1) extends from a motor (not shown) which is mounted on a hood or chassis of a lawn mower. The motor shaft (1) terminates in a cutter blade mounting face (8). The plane of the mounting face (8) is perpendicular to the axis of rotation of the drive line (1). The mounting face (8) has a threaded hole disposed along its axis of rotation. A cutter blade (1) is mounted on the mounting face (8) of the drive line (1) by a bolt (4).

The cutter blade (2) includes tabs (9) which are bent out of the plane of the cutter blade (2) towards the mounting face (8) of the drive line (1). The mounting face (8) includes a series of ramped projections (7) disposed circumferentially around the axis of rotation. In this embodiment, two sets of ramped projections (7) are disposed co-axially around the axis of rotation of the drive line (1). In this embodiment, there are also two tabs (9) extending from the cutter blade (2), one on each side of the mounting hole. Each tab (9) is bent from the blade (2) so that it is integrally joined to the cutter blade (2) along one edge and each tab (9) is radially disposed from the axis of rotation by the same distance as the sets of co-axial ramped projections (7).

If the blade (2) is angularly displaced with respect to the drive line (1) in the direction where the bolt (4) is tightened, such as by the blade (2) colliding with a stone, the tabs (9) will ride up the sloped portion of the ramp.

If the blade (2) is angularly displaced with respect to the drive line (1) in the direction where the bolt (4) is loosened, such as where the blade (2) is braked, then the leading edge of the tabs (9) will move until they meet the steeper stepped portion of the ramp (7). The stepped side of the ramp (7) acts as an abutment to the tab (9). The tab (9) acts like a pawl of a ratchet, and the ramps (7) act like a rack of teeth in a ratchet.

In the embodiment shown in Figure 2, the tabs (9) are resilient so that they will permit the sloped side of the ramp (7) to pass. Alternatively, the ramps (7) themselves may be resilient so that they are displaced as the tabs (9) ride over the sloped sides of the ramps (7). The resilient properties are only exhibited when the tabs (9) travel up the sloped sides of the ramps (7), and not when the tabs (9) abut against the stepped part of the ramp (7).

Although in Figure 2 the tabs (9) which are pressed from the blade (2) in a substantially central position, they (9) may alternatively be pressed from the edge of the blade (2) where the leading edge of the tab (9) is formed from an edge portion of the blade (2). This arrangement requires cutting along two edges of the tabs (9) rather then three.

Figure 3 shows another embodiment of the invention which is very similar to the embodiment of Figure 2. In this embodiment, the cutter blade (2) is attached to an impeller fan (3) and is typically used in hover type rotary mowers.

The drive line (1) from the motor is connected to the impeller (3) for angular movement therewith. The cutter blade (2) is bolted against a face (8) of the impeller (3) through the axis of rotation. The face (8) of the impeller (3) is shaped in the same manner as the mounting face (8) of the drive line (1) described previously. A number of ramped projections (7) extend from the face (8) of the impeller (3) which interact with the tabs (9) of the blade (2). The cutter blade (2) is permitted to be angularly displaced with respect to the impeller (3) only in the direction which tightens the securing bolt (4). In that direction, the tabs (9) will pass over the sloped part of the ramps (7). In the opposite direction, the tabs (9) will abut against the stepped part of the ramps (7) preventing angular displacement of the blade (2) with respect to the impeller fan (3) in a direction which could loosen the securing bolt (4). Again, the tabs (9) or the ramps (7) are preferably resilient.

Figure 4 shows another embodiment of the present invention showing the attachment of a cutter blade (2) and an impeller (3), which forms part of a drive line (1) The face (8) of the impeller (3) includes a plurality of ramps (7) displaced concentrically around the axis of rotation. Each ramp (7) includes a sloped portion and a stepped portion. The face (8) of the impeller (3) also includes a plurality of radial webs (11) which extend further from the axis of rotation than the ramps (7). Alternatively, the radial webs (11) may live inside the ramps (7).

The blade (2) includes a tab (9) which is bent out of the plane of the blade (2) in order that it acts like the pawl of a ratchet. The blade (2) also includes a lug (10) which extends from the blade (2) in a manner similar to that of the peg (5) Figure 1. In this embodiment of the invention, the lug (10) is an integral part of the blade and is bent outwardly at ninety degrees to the blade (2).

The blade (2) may be bolted to the face (8) of the impeller fan (3). In an assembled position, the tab (9) of the cutter blade (2) corresponds in position to the ring of ramps (7), and the lug (10) corresponds in position to the ring of radial webs (11).

In use, the blade (2) is prevented from being angularly displaced significantly with respect to the drive line (1) by the lug (10) which lies between two adjacent webs (11). The blade (2) can be angularly displaced only until the lug (10) abuts against a web (11). To be angularly displaced any further, the lug (10) must break a web (11). In some situations, for example where the cutter blades (2) collide with a stone, the cutter blades (2) are displaced so that the lug (10) breaks an adjacent web (11). The webs (11) may be designed to be sacrificial. In this instance, the cutter blade (2) may only be angularly displaced with respect to the drive line (1) in the direction which tightens the bolt (4).

In this regard, the ramped projections (7) on the impeller (3) interact with the tab (9) extending from the blade (2). The tab (9) acts as a pawl, permitting the angular displacement of the blade (2) with respect to the drive line (1) only in the direction of tightening of the securing bolt (4). The tab (9) is dragged up the sloped portion of the ramp (7). Angular displacement of the cutter blade (2) in the direction which tends to loosen the securing bolt (4) is prevented since the tab (9) abuts against the sloped portion of the ramp (7).

In some instances, it is possible that all the webs (11) of the impeller (3) may become detached. This is likely to be the result of many collisions between the blades (2) and rocks. If this occurs, the lug (10) will become redundant, but the tab (9) remains as an important safety device for reducing the likelihood that the cutter blade (2) will become detached from the drive line (1).

Claims (12)

1. A rotary blade locking device comprising a rotatable drive line including a plurality of ramped projections extending from an end of the drive line.

a rotary blade attachable to the driving member for rotary movement therewith, and including at least one additional projection which extends outwardly from the blade and which, when the blade is attached to the driving member is engageable with at least one of the ramped projections.

2. A locking device according to Claim 1 wherein the ramped projections are disposed concentrically around the axis of rotation of the driving member.

3. A locking device according to Claim 2 wherein each ramped projection comprises a sloped portion and a stepped portion.

4. A locking device according to Claim 3 wherein each additional projection is movable over the sloped portion of a ramped position.

5. A locking device according to Claim 3 wherein each additional projection abuts against the stepped portion of a ramped projection.

6. A locking device according to any proceeding claim wherein the driving member is an impeller and the ramped projections extend outwardly from an external face of an impeller disc.

7. A locking device according to Claim 6 wherein the rotatable blade is attachable to the impeller.

8. A locking device according to any proceeding claim wherein the rotatable blade is detachably mountable on the impeller by means of a bolt.

9. A locking device according to claim 8 wherein the engagement of the tab and the ramps prevents relative angular displacement between the blade and the driving member or the impeller in a direction which tends to loosen the bolt during stopping.

10. A locking device according to any proceeding claim further comprising a lug extending from the blade, and a series of radial webs extending from the end of the driving member or impeller wherein the lug is engageable with the webs for restricting relative angular displacement of the blade with respect to the driving member or impeller.

11. A locking device according to claim 10 wherein the webs are fractured by the lug if the movement of the blades is obstructed.

12. A locking device arranged a constructed substantially as herein described with reference to the accompanying drawings.