GB2243280A

GB2243280A - Adjustment of cylinder lawnmowers

Info

Publication number: GB2243280A
Application number: GB9107730A
Authority: GB
Inventors: Paul David Ducker; Hossein Parvinmehr
Original assignee: QUALCAST GARDEN PROD
Current assignee: QUALCAST GARDEN PROD
Priority date: 1990-04-24
Filing date: 1991-04-11
Publication date: 1991-10-30
Anticipated expiration: 2011-04-11
Also published as: GB9009180D0; GB2243280B; GB9107730D0

Abstract

A lawnmower or similar machine having a cutting mechanism comprising a first cutter item in the form of a cutter cylinder (10) and a second cutter item in the form of a bottom blade (15) arranged to cooperate therewith one of said items being movable relative to the other in order to adjust and define the cutting gap between the cutter cylinder and the bottom blade, has adjusting means (18) operative between the first and second cutter items and which may be released to one state in which it permits relative movement between said items towards and away from each other, and which may be set in a second state in which it prevents or resists relative movement between said items away from each other. In the second state the means may also resist or prevent relative movement towards each other. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO THE ADJUSTMENT OF CYLINDER LAWNMOWERS This invention relates to lawnmowers or similar machines of the type having a cylinder or reel cutter. The invention is particularly concerned with the arrangement of the bottom blade in such lawnmowers or similar machines, which cooperates with the cylinder cutter to perform a shear cutting operation on grass or other material, and with the adjustment of the cutting gap between the bottom blade and the cutter.

A cylinder or reel cutter lawnmower generally includes a rotatable cutter cylinder disposed in the frame of the machine with its axis of rotation parallel to the ground, and a co-operating static or bottom blade to perform the cutting operation. The cutter cylinder has a number of blades formed from strip metal mounted in the cutter cylinder with the plane of the strip disposed at a chosen rake angle to a radius of the cutter, so that a leading outer corner of the strip co-operates with an upper leading corner of the bottom blade, to perform a shear cutting operation. The gap between the cutter cylinder blades and the bottom blade, needs to be maintained sufficiently small for the efficient cutting or slicing of grass or other vegetation by the mower.

A particular consequence of this arrangement is the tendency for the gap between the cylinder cutter blades and the bottom blade to vary during the useful life of the lawnmower as a result of wear. As this gap increases beyond a few thousands of an inch (0.025 mm), the cutting performance of the lawnmower deteriorates substantially.

The significance of this is also increased by the cutting edges or corners of both the cutter blade and the bottom blade becoming radiused or blunted with wear, which further reduces the cutting performance of the mower. The gap between the cutter blades and the bottom blade varies during the life of the mower from various other causes including mechanical vibration and distortion, and as a consequence of impacts due to the trapping of debris between the cutter blades and the bottom blade.

In order to maintain an appropriate gap between the cutter blades and the bottom blade during the life of a mower, traditionally means have been provided to manually adjust the gap, either by moving the cutter cylinder axis with respect to the bottom blade, or by moving the bottom blade with respect to the cutter. For this purpose adjustment means is usually provided, at each side of the cutter cylinder or the bottom blade, on the frame of the machine.

Such adjustment of the cutter cylinder/bottom blade gap is generally a skilled operation requiring the operator to subjectively judge the setting of the machine with only a very slight gap between the cutter blades and the bottom blade, or with a very light contact between them. Such adjustment can be required quite often, depending on the particular design of the lawnmower and. the conditions of its use.

It is an object of the present invention to provide means for adjusting the gap between the cutter blades of the cylinder and the bottom blade, which alleviates the problems of present arrangements for adjusting such gap.

Accordingly the present invention provides in a lawnmower or similar machine having a cutting mechanism comprising a first cutter item in the form of a cutter cylinder and a second cutter item in the form of a bottom blade arranged to co-operate with the cutter cylinder in known manner per se, one of said items being movable relative to the other in order to adjust and define the cutting gap between the cutter cylinder and the bottom blade; in a first aspect of the invention, adjusting means operative between the first and second cutter items and which may be released to one state in which it permits relative movement between said items towards and away from each other, and which may be set in a second state in which it prevents or resists relative movement between said items away from each other; or in a second aspect of the invention, adjusting means operative between the first and second cutter items and which may be released to one state in which it permits relative movement between said items towards and/or away from each other, and which may be set in a second state in which it prevents or resists relative movement between said items towards and away from each other.

Preferably, but not essentially, the first cutter item in the form of the cutter cylinder is mounted to rotate on the frame of the machine about an axis which is fixed relative to the frame while the second cutter item is movably mounted on the frame of the machine.

Preferably the first and second cutter items are resiliently biased towards each other, at least when the adjusting means is released to the state which permits relative movement between them.

Preferably a respective such adjusting means is provided to be operative between the first and second cutter items at each end thereof.

In one embodiment the present invention provides, in a cylinder cutter lawnmower or similar machine, a movably mounted bottom blade arranged to co-operate with the cylinder cutter, in known manner per se to perform a cutting operation, in which said bottom blade is resiliently biased towards engagement with the cutter cylinder; and adjusting means arranged to prevent movement of the bottom blade outwards from a set position.

In the above arrangements or embodiment the adjusting means may include an adjustable member arranged to restrain the bottom blade against outward movement, and the adjusting means is arranged to locate the adjustable member in either direction.

The adjusting member may include an abutment arranged to abut a part of the bottom blade to restrain it against outward movement. Alternatively the adjusting member may be pivotally connected to the bottom blade.

Each such adjusting means may comprise a pivotable lock plate located with respect to one cutter item and having an aperture through which a rod forming the adjustable member and connected to the other cutter item, may freely pass when the lock plate is at a first angle approaching 900 to the axis of the rod, but which will engage and restrain the rod when the lock plate is pivoted away from that first angle to a more acute angle.

In order to promote a fuller understanding of the above, and other aspects of the present invention, some embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 shows a first embodiment of the invention, Fig. 2 shows a second embodiment of the invention, Fig. 3 shows a third embodiment of the invention, and Fig. 4 shows a fourth embodiment of the invention which is an alternative arrangement of that shown in Fig. 3, In each of the Figures 1 to 4 which show various embodiments of the invention, there is shown, in chain dotted outline, the circle 10 which is swept out by a cutter cylinder 11 mounted for rotation, in known manner per se on a shaft 12 in the chassis or frame of a lawnmower indicated generally at 13. In each Figure there is shown a bottom blade 15 having a cutting portion 14 arranged to cooperate with the cutter cylinder 10, in conventional manner per se; and pivotally mounted about an axis 16 in the frame 13 of the lawnmower. At each end of the cutter blade assembly, there is a cutting gap adjusting means, indicated generally at 18 in each Figure. The gap adjusting means 18 are arranged to adjust the gap between a land 19 of the cutting portion 14 and the path of the blades of the cutter 10.

The adjusting means 18 at each end of the cutter and blade arrangement blades comprises an adjustable member in the form of a rod 20, which is slidably mounted in a housing 21 of the adjusting means, which housing is mounted on the frame 13, and coupled at a lower end to either a respective end of the bottom blade or a respective bearing block carrying that end of the cutter shaft 12.

In each of the embodiments, the housing 21 comprises an upper wall 22 in which the rod 20 is slidably mounted and the rod is further guided either by a lower wall 23 of the housing, or the respective bearing block for the shaft 12.

In order to prevent movement of the cutter items towards one another, restraining means 30A is provided to be releasably operative between the housing 21 and the rod 20; while to prevent movement of the cutter items away from one another, restraining means 30B is similarly provided.

The restraining means 30A and 30B each comprise a lock plate 31 which is either loosely mounted in an aperture 32 provided in a side wall 33 of the housing 21 so as to be pivotable (Figures 1 and 2), or is pivoted on an edge 32A of the side wall 33 (Figures 3 and 4). The lock plates 31 each have an aperture 34 of such size that the rod 20 may pass freely through it when the plate 31 is at a first angle of approaching 900 to the axis of the rod, but the rod 20 is gripped by the edges of the aperture when the plate 31 is pivoted away from that first angle to a more acute angle to the axis of the rod 20, as shown in the drawing.

A compression spring arrangement is provided around the rod 20, to be active on the plates 31 of the restraining means 30A and 30B, to bias and retain the plates in their locking position restraining the rod 20. The cross-section of the rod 20 is preferably square and the aperture 34 in the lock plates 31 corresponds in shape to that cross-section.

In the particular embodiment shown in Figure 1 of the drawings, the rod 20 passes slidably through an aperture 40 in a bracket 17 attached to the respective end of the bottom blade, and is provided with an abutment member 42 to engage the under surface of a flange 41 on the bracket 17.

The rod 20 is urged in an upward direction by a spring 46 which is effective between a locknut 45 on the top of the rod 20 and the upper surface of the upper wall 22 of the housing 21. The bottom blade 15 is resiliently biased into engagement with the cutter cylinder by means of a torsion spring 43 which is operative between it and the frame 13 of the machine.

The compression spring arrangement comprises a single spring 35 provided around the rod 20, to be active between the lock plates 31 of the restraining means 30A and 30B, to bias and retain the plates in their locking position restraining the rod 20.

In use, the embodiment of Figure 1 is operated as follows: The restraining means 30A and 30B are both released by pivoting the lock plates 31 by means of the handles 36, allowing the bottom blade to be moved into engagement with the cutter cylinder 10 with the stop 42 hard under the flange 41, by means of the bias spring 46. The restraining means 30A is then re-set to engage the rod 20 thus restraining movement of the rod 20 inwards or upwards as seen in the Figure. The cutter cylinder 10 is then operated for a few revolutions, with the result that the stop 42 and the rod 20 will be moved outwards by the bottom blade moving outwards to a position corresponding to the maximum radius of any blade of the cutter cylinder 10.The restraining means 303 is then re-set to restrain the rod 20 and thus the stop 42, to prevent further outward movement of the blade 15. As the land 19 of the blade 15, or the cutter blades wear, inward movement of the bottom blade 15 by the spring 43 will provide a continuous sharpening action.

When wear of the blades increases the gap, which the scope of outward movement of the blade permitted by the stop 42 can allow to open up during cutting of tough grass, to a value which is too great for successful cutting, the above adjustment process may be repeated to re-set the gap.

The particular embodiment shown in Figure 2, is generally similar to that in Figure 1 with the exception that the rod 20 is pivotally connected to the bracket 17 at a point 50.

Where parts in Figure 2 are the same as those in Figure 1 and have the same function, they are again given the same reference numbers and no further description will be given.

In operation, that is to say while cutting grass, the arrangement of Figure 2 is such that the restraining means 30A and 30B restrain the rod 20, preventing movement thereof, and thus maintaining the cutter blade land 19 in position in co-operation with the cutter 10. In this situation the bottom blade is still biased towards the cylinder under the action of the spring 46 and on releasing of the restraining means 30A and 30B, the spring 46 will move the bottom blade 15 inwards to bring the land 19 into engagement with the cutter 10 to take up any wear.

Restraining device 30A is then re-set, with the result that the bottom blade 15 is then prevented from moving further inwards. If the cylinder is then rotated either manually or under power, the bottom blade 15 will be forced out to a position corresponding to the maximum radius of a blade in the cutter 10, and is prevented from returning again by the restraining device 30A. Once this situation has been achieved, the restraining device 30B is then released fixing the bottom blade in that set position against further outward movement, that is to say ready for use.

The particular embodiment shown in Figure 3 of the drawings is generally similar to that shown in Figure 1, but has some differences as follows.

The two plates 31 of the restraining means 30A and 30B are both arranged to pivotally engage on a respective edge 32A of a side wall portion of the housing 21, instead of being loosely mounted in an aperture as in the previous embodiments. The spring 35 of the spring arrangement which is active on both of the lock plates 31 is replaced by two springs 35A and 35B. Spring 35B is active in a similar manner to the spring 35 on the lock plate 31 of the restraining means 30B, which is above the restraining means 30A in this arrangement; and is retained on the rod 20 by a nut and washer 65 so that the spring 35B also performs the similar function to the spring 46 in the embodiment of Figure 1. The spring 35A is active on the lock plate 31 of the restraining means 30A in a similar fashion to the spring 35 of the previous embodiment, and the reaction of the spring 35A is taken by the lower wall 23 of the housing 21. The operation of the restraining means 30A and 30B on the rod 20 in this embodiment is exactly similar to that of the previous embodiments.

Another difference between the embodiment of Figure 3 and the previous two embodiments, is that the rod 20 is operatively connected to the pivotal bottom blade 15 through the intermediary of a pre-loaded resilient means.

The rod 20 is provided with a fixed shoulder or washer 60 which engages an upper surface of the bracket 17, and with a further washer 63 and associated nut 64 which form the equivalent of the shoulder 52 in the embodiment of Figure 1. A compression spring 62 is interposed between a lower surface of the bracket 17 and the washer 63 and is preloaded to a significant compression. As a result of this, the rod 20 is, so far as the operation of the adjusting means is concerned, firmly attached to the bracket 17 so that the two move together during any of the above discussed adjusting operations.However, if a stone or other solid object becomes trapped between the blades of the cutter cylinder and the bottom blade 15, the bottom blade 15 can pivot downwardly about the axis 16 against the compression of the spring 62 to alleviate the substantial shock loads that would be incurred by this event, irrespective of the restraint of the rod 20 by the restraining means 30A and 303. This provides a safety feature to protect the blades of the cutter and the bottom blade against this eventuality.

The embodiment shown in Figure 4 has adjusting means which is operative between a bearing block 70 for the cutter shaft 12 and the frame 13 of the mower.

In this embodiment, the bottom blade 15 is again pivotally mounted about an axis 16, and is resiliently biased against a fixed stop 71 by means of a strong torsion spring 72 acting between the blade 15 and an abutment 73 about the pivot axis 16. By this means, so far as the operation of the adjusting means 18 is concerned, the bottom blade is fixed in the chassis 13 of the mower. The torsion spring 72 will, however, allow the bottom blade 15 to pivot downwards away from the blades of the cutter in the event of stones or other solid objects becoming trapped to provide a safety feature in a similar manner to that of Figure 3 above.

As mentioned, the adjusting means 18 of this embodiment is active between the bearing block 70 for the cutter shaft 12 and the chassis of the mower, and comprises a housing 21 mounted on the chassis of the mower, a bearing block 70, slidably mounted in the housing 21 and an adjustable member in the form of the rod 20 fixably mounted in the bearing block 70 and slidably mounted in an upper wall 22 of the housing 21.

Restraining means 30A and 30B are provided in the housing 21 to engage the rod 20 in an exactly similar fashion to the embodiment of Figure 3, and similar parts are given similar reference numbers. It should, however, be noted that in the embodiment of Figure 4, the spring 35A acts between the plate 31 of the restraining means 30A and the upper wall 22, while the spring 35B of the restraining means 30B acts between the plate 31 and the bearing block 70, and thus also performs the same general purpose of the spring 46 in the embodiments of Figure 1 and Figure 2, in that it urges the cutter cylinder and bottom blade towards one another by urging the bearing block 70 downwards to engage the cutter with the bottom blade 15.

The operation of the adjusting means 18 of Figure 4 is again generally similar to that of the previous embodiments.

The operation of the restraining means 30A and 30B in any of the above embodiments may be achieved manually as discussed, or automatically, by means not shown, on the completion of some normal operation of the mower in use.

Claims

1. A lawnmower or similar machine having a cutting mechanism comprising a first cutter item in the form of a cutter cylinder, a second cutter item in the form of a bottom blade arranged to co-operate with the cutter cylinder in known manner ner se, one of said cutter items being movable relative to the other in order to adjust and define the cutting gap between the cutter cylinder and the bottom blade, and adjusting means operative between the first and second cutter items, which adjusting means may be released to one state to allow relative movement between said cutter items towards and/or away from each other, and which may be set in a second state in which it prevents or resists relative movement between said cutter items away from each other.

2. A lawnmower as claimed in Claim 1, in which said adjusting means when set in its second state further prevents or resists relative movement between said cutter items towards each other.

3. A lawnmower as claimed in Claim 1 or 2, in which said first and second cutter items are resiliently biassed towards each other.

4. A lawnmower as claimed in any preceding claim, in which a respective such adjusting means is provided to be operative between the first and second cutter items at each end thereof.

5. A lawnmower as claimed in any preceding claim, in which each said adjusting means comprises an adjustable member movably mounted in a housing on the frame of the machine and operatively connected to either the first cutter item or the second cutter item, and the housing is provided with releasable restraining means to engage and so prevent or resist movement of the adjustable member therein.

6. A lawnmower as claimed in Claim 5, in which said adjustable member is connected to the second cutter item in the form of the bottom blade which is movably mounted in the frame while the first cutter item in the form of the cutter cylinder is arranged to rotate about an axis which is fixed relative to the frame.

7. A lawnmower as claimed in Claim 6, in which the adjustable member is formed with an abutment to abut a part of the bottom blade to restrain it against outward movement from the first cutter item in the form of the cutter cylinder.

8. A lawnmower as claimed in Claim 6, in which the adjustable member is pivotally connected to a part of the bottom blade.

9. A lawnmower as claimed in Claim 5, in which the adjustable member is so connected to a bearing block which is slidably mounted in the frame to carry one end of a shaft carrying the first cutter item in the form of the cutter cylinder, and the adjustable member is rigidly connected to that bearing block.

10. A lawnmower as claimed in Claim 9, in which the second cutter item in the form of a bottom plate is pivotally mounted in the frame of the mower and resiliently biassed towards the cutter cylinder against a fixed stop on the frame of the machine.

11. A lawnmower as claimed in Claim 7, in which a preloaded resilient means is interposed between said adjustable member and said part of the bottom blade so that relative movement between the adjustable member and the bottom blade away from each other may occur when the preload in the resilient means is exceeded.

12. A lawnmower as claimed in any one of Claims 6 to 11, in which the adjustable member is resiliently biassed in a direction to move the first and second cutter items towards each other.

13. A lawnmower as claimed in any one of Claims 6 to 12, in which the adjustable member comprises a rod slidably mounted in said housing.

14. A lawnmower as claimed in Claim 13, in which said rod is a square cross-section.

15. A lawnmower as claimed in any one of Claims 6 to 14, in which each said releasable restraining means comprises a lock plate having an aperture through which said adjustable member passes and pivotally mounted in said housing for movement between one position or state in which it allows free movement of the adjustable member through said aperture, and a second position or state in which it engages the adjustable member to so prevent or resist movement of the adjustable member relative to the housing.

16. A lawnmower as claimed in Claim 15, in which each said lock plate is resiliently biassed towards said second position.

17. A lawnmower as claimed in Claim 15 or 16, in which two such restraining means are provided in each said adjusting means, one operative to prevent or resist movement of said first and second cutter items towards each other and a second operative to prevent or resist movement of said first and second cutter items away from each other.

18. A lawnmower as claimed in Claim 17, in which said lock plates are resiliently biassed to their second position by means of a compression spring disposed between them.

19. A lawnmower as claimed in Claim 17, in which said lock plates are each resiliently biassed to their second position by means of a respective compression spring disposed between the respective lock plate and a respective wall of the housing.

20. A lawnmower as claimed in Claim 18 or 19, in which each said compression spring is disposed around said adjustable member.

21. A lawnmower having a cutter cylinder and a bottom blade with adjusting means operative there between, substantially as herein described with reference to Figure 1, 2, 3 or 4 of the accompanying drawings.