GB2187925A - Improvements in or relating to vegetation cutters - Google Patents

Abstract

A wheeled rotary lawnmower has a driving motor (5) with an 3 output shaft (11) having a part of a non-circular cross-section over which fits a blade clamp member (16). The member (16) has a peripheral flange (17) and a shank (17a). A cutter blade (18) loosely mounted upon the shank (17a) is secured thereon by a lock nut (19), a washer (20) being interposed between the blade (18) and the lower face of the shank (17a). Spring washers (21) interposed between the flange (17) and the blade (18) are compressed as the lock nut (19) is screwed up and act as a safety clutch for the blade (18) allowing rotary movement of the blade relative to the shaft in the event of overload. The construction also includes means for holding the shaft (11) against rotation when the nut (19) is to be released. <IMAGE>

Description

SPECIFICATION Improvements in or relating to vegetation cutters This invention relates to vegetation cutters and has particular reference to cutters of the rotary type that is to say cutters in which cutting is effected by a rotary cutter assembly which may be a cutter blade.

The use of such cutters under arduous conditions may cause serious overloading of the motor driving the rotary assembly. Such overloading may damage the motor and if the latter is an electric motor may result in current flow sufficient to burn out the motor windings.

Moreover, if the motor drives the cutter assembly through a speed reduction gearing overloading may also result in damage to the gears particularly if overloading occurs over a relatively prolonged period.

It is an object of the present invention to provide a construction in which the likelihood of damage to the driving motor is reduced.

According to the present invention, a vegetation cutter comprises a drive motor, an output shaft driven by the motor, a cutter assembly mounted on the output shaft and in driven connection therewith via means permitting movement of the cutter assembly relatively to the shaft in the event that the assembly experiences a load greater than a preset load.

The means may comprise a clutch which may be a friction clutch.

The cutter may further comprise a first clamping member mounted upon the output shaft for rotation there with, a second clamping member also mounted upon the output shaft at a location spaced from the first clamping member, and in which the cutter assembly is mounted upon the shaft between the first and second clamping members and in which rotation of the shaft is transferred via the first clamping member to the cutter blade assembly via said means.

The means may comprise a resilient device compressed between the first clamping means and the cutter assembly.

The resilient device may be at least one spring washer loosely mounted upon the output shaft.

The cutter may further comprise means for releasably locking the cutter assembly to the output shaft.

There may also be a locking member secured to the output shaft for rotation therewith, said locking member being adapted to be releasably secured to the cutter assembly.

The locking member may comprise a disc having one or more locking surfaces, and in which the cutter assembly also has one or more locking surfaces, the arrangement being such that the cutter assembly is releasably locked to the shaft by aligning the or one of the locking surfaces on the locking member with the or one of the locking surfaces on the cutter assembly and engaging a locking device with the aligned surfaces.

The disc may have one or more apertures in peripheral slots, in which the cutter assembly has one or more apertures, and in which the locking device comprises a locking pin.

The locking member may be the second clamping member.

The second clamping member may be rotatable with the output shaft and is adapted to be lockable to the cutter assembly.

The first clamping member may comprise a flanged cylinder and in which the second clamping member is mounted upon the first clamping member for rotation therewith.

The cylinder may have an end portion formed to receive the second clamping member.

The end portion may have a surface adapted to form a stop to movement of the second clamping member towards the first clamping member.

The first and second clamping member may be retained in position on the output shaft by a lock nut screwed on to the output shaft.

The lock nut may be adapted to retain the second clamping member against the stop.

The first clamping member may be adapted to limit the extent to which the lock nut is screwable on to the output shaft.

The output shaft may extend from a casing which may have or be provided with a wall round the shaft.

The motor may be in driving connection with the output shaft via a rotary speed reduction gearing The cutter assembly may comprise a cutter bar.

By way of example only, embodiments of the invention will now be described in greater detail with reference to the accompanying drawings of which: Fig. 1 is an underneath view of part of a first embodiment shown in partly exploded fashion, Fig. 2 is a section through a part of the mechanism of the first embodiment, Fig. 3 is a vertical section of part of a second embodiment, Figs. 4 and 5 are plan view and elevation respectively of a cutter blade, Fig. 6 is a plan view of a blade clamp nut, Figs. 7 and 8 are, respectively, sections on the lines VII-VII and VIII-VIII of Fig. 6, Figs. 9 and 10 are, respectively, plan view and elevation of a locking washer, Figs. 11 and 12 are, respectively, plan view and section on the line XII-XII (Fig. 11) of a lock nut, Figs. 13 and 14 are, respectively, plan view and section on the line XIV-XIV (Fig. 13) of a spring washer.

Fig. 1 is an underneath view of a wheeled rotary lawnmower comprising a housing 1 mounted upon rear wheels 2 and forward wheels 3. Wheels 3 are mounted upon brackets 4 pivotally attached to the side walls of the housing 1 in a manner that permits the height above ground level of the axles of the wheels 3 to be varied to vary cutting height of the mower.

Accommodated within the upper part (in the working orientation of the mower) is an electric motor 5 whose armature shaft 6 extends downwardly through an internal wall 7 of the housing 1. Secured to the undersurface of the wall 7 is a casing 8 into which the shaft 6 extends. The casing 8 is formed internally with an elongate boss 9 which accommodates.

a bearing liner 10 that supports an output shaft 11 whose upper end is supported in a second bearing sleeve 12 held in the upper wall 13 of the casing 8. Secured to the shaft 11 adjacent the upper end thereof is a gear wheel 13 in mesh with a pinion 14 carried on the lower end of the armature shaft 6. Between the boss of the gear wheel 13 and the upper end of the boss 9 is a thrust bearing 15.

The output shaft 11 projects externally from the casing 8 and, over part of the length of its projecting end is of non-circular cross-section. For example, the part may have "flats" over which fit a blade clamp member 16 with a peripheral flange 17 and a shank 17a.

Loosely mounted on the shank 17a is a cutter blade 18 only part of which is shown in Fig.

2. The blade 18 has a circular hole through which the shank 1 7a passes with some clearance. The blade 18 is secured in place by a lock nut 19 screwed on to a threaded end of the shaft 11. A washer 20 is interposed between the blade 18 and the lower face of the shank 17a.

Positioned between the flange 17 of the clamp member 16 and the blade 18 are three spring washers 21 of known design arranged back to back as shown. The washers 21 have large diameter central holes and fit loosely round the clamp member 16.

The act of screwing the lock nut 19 on to the shaft 11 applies pressure to the spring washers 21 and, when the nut 19 is fully screwed up, clamping the washer 20 on to the lower face of the shank 17a, a predetermined pressure has been applied.

In action, rotation of the shaft 11 rotates the blade 18 via the clamp member 16 and the washers 12. If, during use, the blade experiences a load of a value greater than a preset value as determined by the pressure applied to the spring washers, the blade 18 slips slightly relatively to the shaft 11. In that way, overloading of the motor 5 is avoided, as is damage to the gear wheel 13 and pinion 14.

From time to time, it becomes necessary to remove the cutter blade 18 for example for sharpening and removal is effected by undoing the lock nut 19. Removal is sometimes difficult because it is not easy to hold the shaft 11 against rotation with the lock nut 19.

The present invention also provides a simple means of holding the shaft 11 against rotation when it is desired to undo the clamp nut 19.

Fig. 3 is a vertical section through part of the driving mechanisms of a rotary mower of the general form shown in Fig. 1 which incorporates such means.

The output shaft 6 of the gear mechanisms is threaded over the end portion of its length as indicated at 22. That part 23 of the shaft 6 immediately adjacent the threaded length 22 is of non-circular cross-section. The transverse cross-section of part 23 will be described below. Located over the portion 23 is a blade clamping member 24 similar in general form to member 16 of the embodiment shown in Fig. 1. Member 24 has a flange 25 and its shank 26 is formed with diametrically opposite 'flats' 27 as can be seen from Figs. 6 and 7 and which provide shoulders 28 on the shank.

The bore of the shank 26 also has flats as indicated at 29 in Fig. 6.

The transverse cross-section of the part 23 of the shaft 6 is contoured in a manner generally similar to that of the bore of the shank 26 so the latter fits the part 23 closely.

The flange 25 on the clamp forms a seating surface for the uppermost of three spring washers 29, the lowermost of which seats on the central portion of the cutter blade 30. The washers 29 fit loosely round the shank 26 of the member 24.

Blade 30 (Figs. 4 and 5) is strip-shaped having cutting edges 31 machined over part of the blade leading edges. To the rear (in the direction of rotation) the surface of the strip is up-turned to provide a triangular "wing" 32.

Centrally of its length, the blade 30 has a round hole 33 which fits with clearance over the lower part (as seen in Fig. 3) of the shank 26 of the member 24. In diametrically opposed positions, with respect to the centre of the hole 33, are formed two smaller holes 34.

Located over the end of the shank 26 is a washer 35 shown in more detail in Figs. 9 and 10. The washer 35 has a central hole 36 with flats 37 enabling the washer to seat over the flats 27 on the shank 26 of the member 24. The outer periphery of the washer 35 has a series of equi-spaced, semi-circular slots 38.

The washer 35 is sized so that the centres of the slots 38 lie on a circle whose radius is equal to the distance between the centre of the hole 33 and that of either of the holes 34.

The lock nut 39 that is used to retain the blade 30 and washer 35 in position on the shaft 6 and to apply pressure to the spring washers 29 is of two-part construction. A hexagonal nut part 40 is contoured at one end to receive the smaller end of a dome part 41.

The dome part 41 is sized so that when the nut is screwed over the end 22 of the shaft 6, the larger end of the part seats on to an area of the washer spaced from the shoulders 28.

As the nut is screwed in to position, it applies pressure to the washer 35 and via the blade 30 to the spring washers 29 to provide the slipping clutch action described above.

The apex angle of the dome part 41 is somewhat exaggerated in Fig. 3 for the sake of clarity. Fig. 12 shows the domed part more accurately and it will be appreciated that, when lock nut 39 is fully screwed home to abut the lowered face of the shank 26, a predetermined pressure has been applied to the spring washers.

When it is desired to remove the blade 30, a user first holds the latter against rotation and rotates nut 39. As nut 39 rotates, the frictional engagement of washer 35 therewith also causes the latter to rotate. Rotation continues until one of the semi-circular slots 38 is aligned with one of the holes 34 in the blade 30. Using a screwdriver or similar implement, the user is able to lock the washer 35 to the blade 30 and in this way to hold the shaft 6 against rotation merely by grasping the blade 30 and holding it stationary. The lock nut 39 can then be unscrewed and taken off thus permitting removal of the washer 35 and then the blade.

It is not essential to use a disc-shaped washer between the lock nut 39 and the blade 30. Components other than disc-shaped articles can be used, for example a rectangular square strip. Furthermore, other ways of securing the washer or component to the blade may be used.

It will be appreciated that use of a lock nut with a domed portion is not essential. A lock nut of conventional form, i.e. similar to lock nut 19 described above could be used although in this case, the thickness of the washer 35 or equivalent part must exceed the depth of the flats 27 in order that the spring washers 29 will be loaded as the lock nut is screwed in position.

A further feature of the invention will now be described with reference to Fig. 2.

The boss 9 stems from a flattened area 42 of the casing 8, the area being of generally circular form when viewed in plan. Round the rear 42 is a circular wall 43 that closely encircles the flange 17 on the clamp nut 16.

The wall 43 serves to limit access o the bearing sleeve 10 of dirt and other deleterious matter so extending the life of the bearing. In addition, the wall 43 effectively prevents lengths of cut grass or other vegetable matter from becoming entangled round the shaft 11.

The friction clutch may also take forms other than that described above. It is important that the clutch can readily be loaded to a preset value and that overload is not possible.

In the example described above, the spring means are loaded or compressed as the lock nut is screwed on to the shaft. The lock nut cannot be screwed beyond the position in which it contacts the end face of the clamp member.

The friction clutch may be incorporated in air-cushion-supported mowers as may be the mechanism for facilitating removal of the cutter- blade. In addition, those features may also be embodied in brush cutters employing either cutter bars or serrated or plain cutter discs.

Claims (22)

1. A vegetation cutter comprising a drive motor, an output shaft driven by the drive motor, a vegetation cutter assembly mounted upon the output shaft and in driven connection therewith via means permitting rotary movement of the cutter assembly relatively to the output shaft in the event that the cutter assembly experiences a load greater than a preset load.

2. A cutter as claimed in claim 1 in which the means comprises a clutch.

3. A cutter as claimed in claim 2 in which the clutch is a friction clutch.

4. A cutter as claimed in claim 1, 2 or 3 and further comprising a first clamping member mounted upon the output shaft for rotation therewith, a second clamping member also mounted upon the output shaft at a location spaced from the first clamping member, and in which the cutter assembly is mounted upon the shaft between the first and second clamping members and in which rotation of the shaft is transferred via the first clamping member to the cutter blade assembly via said means.

5. A cutter as claimed in claim 4 in which the means comprises a resilient device compressed between the first clamping means and the cutter assembly.

6. A cutter as claimed in claim 5 in which the resilient device comprises at least one spring washer loosely mounted upon the output shaft.

7. A cutter as claimed in any one of the preceding claims and further comprising means for releasably locking the cutter assembly to the output shaft.

8. A cutter as claimed in any one of claims 1-6 and further comprising a locking member secured to the output shaft for rotation therewith, said locking member being adapted to be releasably secured to the cutter assembly.

9. A cutter as claimed in claim 8 in which the locking member comprises a disc having one or more locking surfaces, and in which the cutter assembly also has one or more locking surfaces, the arrangement being such that the cutter assembly is releasably locked to the shaft by aligning the or one of the locking surfaces on the locking member with the or one of the locking surfaces on the cutter assembly and engaging a locking device with the aligned surfaces.

10. A cutter as claimed in claim 9 in which the disc has one or more apertures in peripheral slots, in which the cutter assembly has one or more apertures, and in which the locking device comprises a locking pin.

11. A cutter as claimed in claim 8, 9 or 10 when appended to any one of claims 4-6 in which the locking member is the second clamping member.

12. A cutter as claimed in claim 4, 5 or 6 in which the second clamping member is rotatable with the output shaft and is adapted to be lockable to the cutter assembly.

13. A cutter as claimed in claim 12 in which the first clamping member comprises a flanged cylinder and in which the second clamping member is mounted upon the first clamping member for rotation therewith.

14. A cutter as claimed in claim 13 in which the cylinder has an end portion formed to receive the second clamping member.

15. A cutter as claimed in claim 14 in which the end portion has a surface adapted to form a stop to movement of the second clamping member towards the first clamping member.

16. A cutter as claimed in claim 15 in which the first and second clamping members are retained in position on the output shaft by a lock nut screwed on to the output shaft.

17. A cutter as claimed in claim 16 in which the lock nut is adapted to retain the second clamping member against the stop.

18. A cutter as claimed in claim 17 in which the first clamping member is adapted to limit the extent to which the lock nut is screwable on to the output shaft.

19. A cutter as claimed in any one of the preceding claims in which the output shaft extends from a casing, and in which the casing has or is provided with a wall round the shaft.

20. A cutter as claimed in any one of the preceding claims in which the motor is in driving connection with the ouptut shaft via a rotary speed reduction gearing.

21. A cutter as claimed in any one of the preceding claims in which the cutter assembly comprises a cutter bar.

22. A vegetation cutter substantially as herein described with reference to and as illustrated by Figs. 1 and 2 or Figs. 3-13 of the accompanying drawings.