WO2008066442A1

WO2008066442A1 - Cylinder lawn mower

Info

Publication number: WO2008066442A1
Application number: PCT/SE2007/001020
Authority: WO
Inventors: Mats Fischier
Original assignee: Mats Fischier i Båstad AB
Priority date: 2006-11-27
Filing date: 2007-11-21
Publication date: 2008-06-05
Also published as: SE0602509L

Abstract

A cylinder lawn mower, comprising an engine, a fixedly arranged abutment (2) and a cylinder means (1 ) with at least one blade (5). The engine is arranged to rotate said cylinder means (1 ) about a longitudinal axis at a speed in the range 700-5000 rpm. Each blade (5) is, by rotation of the cylinder means (1 ), movable to a cutting position (K), in which the blade (5) cooperates with the abutment (2) to allow grass cutting, the at least one blade (5) being supported by a cylinder shaft (3), which is extended along said longitudinal axis, via a plurality of blade supporting elements (4) which are distributed along said cylinder shaft (3) at a distance (A) from each other in the range 10-30 mm, and each blade (5) having a width (B1 ) in the range 0.5- 2.5 mm.

Description

CYLINDER LAWN MOWER

Field of the Invention

The present invention relates to a lawn mower, and more specifically a cylinder lawn mower comprising a fixedly arranged abutment and a cylinder means with at least one blade, each blade, by rotation of the cylinder means, being movable to a cutting position, in which the blade cooperates with the abutment to allow grass cutting.

Background Art

Prior art cylinder lawn mowers of the type described by way of introduction, as disclosed in, for instance, US2827752, usually comprise a cylinder means with a plurality of peripherally mounted helical blades, which cooperate with an abutment arranged at the underside of the cylinder means.

When cutting grass by means of such a cylinder lawn mower, the vegetation on a lawn, hereinafter referred to as grass, is inserted between the respective blades and the abutment. The cooperation of the blades and the abutment yields an almost scissor-like cutting of the grass, which is preferable since it results in a distinct cutting surface which thus is kind to the grass. This is in contrast to grass cutting using a rotary lawn mower, in which the grass is torn off, resulting in a brush-like cutting surface. In power cylinder lawn mowers as disclosed in EP1769665 for instance, the blades are in operation subjected to radial and tangential forces which act to bend them outward. The longer the blades, the greater the stress at a given speed. To counteract outward bending, the blades are given relatively great dimensions to achieve the necessary rigidity. When cutting grass, the engagement of the blades and the abutment with the grass results in wear that causes the blades and the abutment to lose their sharpness. This wear can to some extent be compensated for by letting each blade make slight contact with the abutment when passing the same, which contact results in sharpening of the blade and the abutment. The cutting edges can also be sharpened by back lapping, by which is meant that the cylinder means is rotated in the reverse direction, in which case a grinding agent is continuously supplied to the contact surfaces between blades and abutment.

Figs 1a-1c, to which reference is now made, schematically illustrate a cylinder means 101 with four blades 105 and an abutment 102 for a conventional cylinder lawn mower.

In Fig. 1a, the blades 105 and the abutment 102 are in a ground state. The abutment 102 has a cutting edge 109 with a back angle α. Also the blades 105 have a cutting edge 108 with a back angle α. As shown in the figure, the cutting edges 108, 109 can be separated from the respective back angles α by a landing area which, after mounting and break-in of blades and abutment, may have a width of one or a few millimetres. These landing areas are to be seen more distinctly in the broken-away partial enlargement in the figure.

The abutment 102 is located such that the blades 105 make slight contact with the abutment 102 when passing.

Fig. 1 b illustrates the blades 105 and the abutment 102 in a state after a period of use.

The slight contact of the blades 105 with the abutment 102 causes, as mentioned above, the cutting edges 108,109 to maintain their sharpness, but at the same time both the blades 105 and the abutment 102 are worn down. For the contact between the blades 105 and the abutment 102 to be maintained in spite of this wearing down, the abutment 102 and the cylinder means 101 must be moved toward each other at regular intervals.

Said wearing down results in the landing areas 110, 111 growing on the blades 105 and the abutment 102. The landing areas 110, 111 separate, as mentioned above, the cutting edges 108, 109 from the back angle α. In Fig. 1b, the worn portions of the blades 105 and the abutment 102 are indicated by dashed lines in the broken-away partial enlargement.

The growth of the landing areas 110, 111 has a negative effect on the cutting capacity of the cylinder lawn mower. As mentioned above, the blades 105 have a helical extent, which means that the cooperation of each blade 105 with the abutment 102 when cutting grass starts in one side of the abutment 102 and then continues steplessly along the extent of the abutment 102. When part of the blade 102 has cooperated with the abutment 102 for cutting grass, cut grass will be arranged on the landing areas 110, 111 , between the blade 105 and abutment 102, which acts to separate blade 105 and abutment 102. As a result, a subsequent part of the blade 105 starting to cooperate with the abutment 102 for cutting grass is not allowed to make contact with the abutment 102. This reduces the scissor-like cutting action and instead the grass is torn off when squeezed between the blade 105 and the abutment 102. As the landing areas 110, 111 grow, the cylinder lawn mower will thus at an increasing extent "chew" the grass. This is evident from Fig. 1c, where the conventional cylinder lawn mower is shown in operation. The blades 105 and the abutment 102 are shown in a state after a long period of use and have thus been subjected to extensive wear, resulting in large landing areas 110, 111 being formed. It is shown in the figure how the grass, when it is to be cut, is arranged almost parallel to the landing areas 110, 111 and is pressed between blade 105 and abutment 102. The grass is torn off, resulting in brush-like cutting surfaces.

When the landing areas 110, 111 exceed a given threshold value, the cutting capacity of the cylinder lawn mower is reduced to such an extent that regrinding of both blades 105 and abutment 102 is required. The regrinding process is quite difficult and takes a long time. First both cylinder means and abutment must be dismounted from the cylinder lawn mower.

After that, cutting edges and back angles must be ground by means of grinding machines for both blades and abutment. Regarding the blades of the cylinder means, regrinding must take place so that the cylinder means maintains its cylindrical shape.

The grinding machines are relatively expensive pieces of equipment, and therefore the grinding work is frequently performed by specialist firms to which the components that require grinding are sent. Finally, the cylinder means and the abutment must again be mounted on the cylinder lawn mower and be accurately set relative to each other.

In establishments where commercial cylinder lawnmowers are used, that is establishments such as golf courses in which frequent mowing is necessary, cylinder lawn mowers are usually provided in such a number that a sufficient cutting capacity is obtained even with certain cylinder lawn mowers being taken out of operation for regrinding. The blades and the abutment of commercial cylinder lawn mowers are, as a rule, worn to such an extent that regrinding is necessary several times per season.

The cylinder means of a commercial power cylinder lawn mower usually has a length in the range 400-1000 mm and a diameter in the range 100-250 mm and supports a plurality of blades with a width in the range 4-8 mm. There is thus a need for a cylinder lawn mower, especially a commercial cylinder lawn mower, which can be used for relatively long periods without requiring regrinding.

Summary of the Invention In view of that stated above, an object of the present invention is to provide a cylinder lawn mower which in operation maintains a satisfactory cutting capacity without requiring regrinding.

A further object is to provide such a cylinder lawn mower which is power-operated. To achieve at least one of these objects, and also other objects that will appear from the following description, a cylinder lawn mower is provided according to the present invention having the features stated in claim 1. Embodiments of the cylinder lawn mower are defined in claims 2-13 which depend on claim 1. More specifically, according to the present invention a cylinder lawn mower is provided, comprising an engine, a fixedly arranged abutment and a cylinder means with at least one blade. The engine is arranged to rotate said cylinder means about a longitudinal axis at a speed in the range 700-5000 rpm, more preferably in the range 1500-5000 rpm. Each blade is, by rotation of the cylinder means, movable to a cutting position, in which the blade cooperates with the abutment to allow grass cutting. The at least one blade is supported by a cylinder shaft, which is extended along said longitudinal axis, via a plurality of blade supporting elements which are distributed along said cylinder shaft at a distance from each other in the range 10-30 mm, each blade having a width in the range 0.5-2.5 mm.

By width of the blade is meant the extent of the blade in the tangential direction when looking sideways at the cylinder means, as illustrated in, for instance, Fig. 3.

In this way, a cylinder lawn mower is provided, whose blades do not require frequent regrinding to maintain a satisfactory cutting capacity. The reason for this is that the relatively small width of the blades makes it possible to ensure that the landing areas formed in operation by wear do not exceed a threshold value, at which regrinding is required. When a landing area has formed over the entire end face of the blade, it cannot grow any more, and the width of the blade is selected in such a manner that the cutting capacity of the cylinder lawn mower is maintained also when a maximum landing area has formed. The blade supporting elements arranged along the cylinder shaft support the blades and provide a dimensionally stable attachment thereof also at relative high speeds, that is 700-5000 rpm.

In one embodiment, also the abutment may have a width in the range 0.5-2.5 mm. This also helps to ensure that the landing areas are kept below said threshold value. In another embodiment, the at least one blade may be arranged to make slight contact with the abutment when passing the cutting position. This ensures that the cutting edges of the blades and the abutment can be kept sharp in operation or by back lapping.

In a further embodiment, the blade supporting elements may be provided with recesses for receiving said blades. Each blade can be designed in the shape of a curved beam which is clamped in said recess to obtain a helical extent of said blade. This allows cost-effective manufacture of said blades. The blades may be fixedly connected to the cylinder means by a friction joint formed between each blade and the associated recess of the respective blade supporting elements. In order to additionally secure the attachment of the blades, they can be connected to the blade supporting elements by welded joints. In another embodiment of the present invention, the blade supporting elements are fixedly connected to the cylinder shaft. The blade supporting elements may consist of discs.

In yet another embodiment the blades are made of a highly abrasion- resistant material, such as the steel quality Docol^® M. This ensures a long life of the cylinder means and its blades.

The blades may be fixedly mounted on the cylinder means, which can be provided, for example, by friction joints and and/or welded joints.

The cylinder means may have a length in the range 400-1000 mm. Such a relatively long cylinder means has relatively long blades. In operation, the outward bending of the blades will, by the blades being subjected to radial and tangential forces, be counteracted by the dimensionally stable attachment of the blades provided by the closely arranged blade supporting elements. The cylinder lawn mower can be a ride-on lawn mower and also comprise a plurality of cylinder means and associated abutments.

Furthermore, according to the present invention a cylinder lawn mower is provided, comprising an engine, a fixedly arranged abutment and a cylinder means with at least one blade. The engine is arranged to rotate said cylinder means about a longitudinal axis at a speed in the range 700-5000 rpm, more preferably in the range 1500-5000 rpm. Each blade is, by rotation of the cylinder means, movable to a cutting position, in which the blade cooperates with the abutment to allow grass cutting, the abutment having a width in the range 0.5-2.5 mm. This results in a cylinder lawn mower, whose abutment and blades do not require frequent regrinding in order to maintain a satisfactory cutting capacity. The relatively small width of the abutment ensures that the landing areas formed in operation by wear do not exceed a threshold value, at which regrinding is required. In one embodiment, the at least one blade can be supported by a cylinder shaft extended along said longitudinal axis, via a plurality of blade supporting elements which are distributed along said cylinder shaft at a distance from each other in the range 10-30 mm, each blade having a width in the range 0.5-2.5 mm. This also helps to ensure that the landing areas are kept below said threshold value.

In another embodiment, the at least one blade may be arranged to make slight contact with the abutment when passing the cutting position. This ensures that the cutting edges of the blades and the abutment can be kept sharp in operation or by back lapping.

Brief Description of the Drawings

An embodiment of the present invention will now be described by way of example and with reference to the accompanying drawings.

Fig. 1a is a schematic cross-section of a cylinder means and an abutment for a conventional cylinder lawn mower in a newly ground state.

Fig. 1 b is a schematic cross-section of the cylinder lawn mower in Fig. 1a after a period of use. Fig. 1 c is a schematic cross-section of the cylinder lawn mower in Fig.

1a in operation and after a long period of use.

Fig. 2 is a schematic perspective view of a cylinder means and an abutment for a cylinder lawn mower according to the present invention. Fig. 3 is a schematic cross-section of the cylinder means and the abutment shown in Fig. 2.

Description of Embodiments

Fig. 2, to which reference is made, shows a cylinder means 1 and an abutment 2 for a cylinder lawn mower according to the present invention. The cylinder means 1 comprises a cylinder shaft 3 extending along an axis of rotation.

The cylinder shaft 3 supports a plurality of blade supporting elements 4. The blade supporting elements 4 are fixedly arranged on the shaft 3 and spaced from each other a distance A in the range 10-30 mm. Four helically extended blades 5 are supported by the shaft 3 via said blade supporting elements 4. It will be appreciated, however, that the cylinder means 1 according to the invention may have a number of blades which is greater or smaller than four. The blade supporting elements 4 are in the shown embodiment designed in the shape of discs which are formed with peripheral recesses 6 for receiving the blades 5. By the cylinder means 1 comprising four blades 5, each disc has four recesses 6 which are equidistantly spaced along the circumference of the disc and, thus, spaced from each other at an angle of 90°. However, it will be appreciated that the recesses could also be irregularly distributed along the circumference of the disc.

The blade supporting elements 4 may, of course, be designed in other manners. Thus, an element may, for instance, be in the form of a hub or a spindle, on which a peripheral ring is supported, by means of spokes, at a radial distance from the cylinder shaft 3.

The blades 5 can be fixedly mounted by welded joints and/or friction joints. By friction joints is meant clamp joints, as will be described below, and also screw joints. The blades 5 can be made so as to have a helical extent.

Alternatively, each blade 5 may have the shape of a curved or arched beam. When mounted on the cylinder means 1 , the blade 5 obtains its helical extent by being bent to be clamped in the associated recesses 6 of the blade supporting elements 4. If a blade 5 clamped in the manner described above is mounted in the blade supporting elements 4, the blade 5 can be arranged to form a friction joint 7 in the form of a clamp joint with the recess 6 of the respective blade supporting elements 4. The friction joints 7 ensure that the blade 5 is kept in place during operation. In order to additionally secure the fixing, the friction joints can be supplemented with welded joints.

The inventive cylinder lawn mower further comprises an engine (not shown) for rotation of the cylinder means 1 at a speed in the range 700-5000 rpm, more preferably in the range 1500-5000 rpm. The engine also comprises a drive mechanism, such as a hydraulic unit or a chain or belt arrangement, to transfer the engine power to the cylinder means 1.

Said friction joints 7 between the blades 5 and the recesses 6 of the blade supporting elements 4 are adjusted so as to provide safe securing of the blades 5 on rotation of the cylinder means 1. Fig. 3, to which reference is now also made, illustrates schematically a cross-section of the cylinder means 1 and the abutment 2 shown in Fig. 2.

The blades 5 have a width B1 , that is an extent in the tangential direction, and the abutment 2 has a width B2 in the corresponding direction. The width B1 is in the range 0.5-2-5 mm, and more preferably in the range 1- 2 mm. Also the abutment 2 may have a relatively narrow width B2 in the range 0.5-2.5 mm, and more preferably in the range 1-2 mm.

The relatively small width B1 of the blades 5 makes it possible to design them, as described above, in the shape of curved means which are clamped in the recesses 6 of the blade supporting elements 4 to obtain a helical extent of the blades 5.

By rotation of the cylinder means 1 , each blade 5 is movable to a cutting position K, in which it cooperates with the abutment 2 to allow grass cutting. Each blade 5 has a cutting edge 8. Also the abutment 2 has a cutting edge 9.

The abutment 2 is arranged so that the blades 5 make slight contact with the abutment 2 when passing the cutting position K. This ensures that the cutting edges 8, 9 of the blades 5 and the abutment 2 are kept sharp in operation.

The cutting edge 8 of each blade is followed by a landing area 10. Also the cutting edge 9 of the abutment 2 is followed by a landing area 11. The landing areas 10, 11 thus consist of the end faces of the respective blades 5 and the abutment 2, which end faces, when passing the cutting position K, make contact with each other.

The blades 5 and the abutment 2 may each be provided with a back angle for minimising of said landing areas 10, 11 (not shown).

As the blades 5 and the abutment 2, because of the mutual slight contact, are being worn down, the distance between blades 5 and abutment 2 is adjusted so as to maintain the mutual contact.

If there should be a need of sharpening the cutting edges 8, 9 of the blades 5 and the abutment 2, such sharpening can be performed in a conventional manner by back lapping. This means that the cylinder means 1 is rotated in the reverse direction while simultaneously a grinding agent is being supplied. The contact between the abutment 2 and the blades 5 results in the desirable sharpening being provided.

If the blades 5 and the abutment 2 are provided with back angles, the landing areas 10, 11 will grow as the blades 5 and the abutment 2 are being worn down. However, if there are no such back angles, the landing areas 10, 11 will have a significantly unchanged size during wearing down.

The width B1 of the blades 5 and the width B2 of the abutment 2 ensure, however, that the size of the landing areas 10, 11 cannot exceed a given threshold value, at which regrinding would be necessary to maintain a satisfactory cutting result. Consequently, the blades 5 and the abutment 2 are so narrow and have such a shape that the landing areas 10, 11 cannot become so large as to constitute a problem. Thus, each blade 5 may have such a width B1 and such a shape that the landing area 10 cannot exceed the cross-sectional area of the blade 5.

The inventive cylinder lawn mower may consequently be used until the blades 5 or the abutment 2 are completely worn down.

In order to obtain as long an operating time as possible, the blades 5 and the abutment 2 should be made of a highly abrasion-resistant material. As an example which does not limit the invention, the steel quality Docol^® M, which is sold by SSAB, can be mentioned as a suitable material for the blades 5 and the abutment 2.

Even if the blades 5 are narrow, and thus relatively weak, the inventive cylinder lawn mower exhibits a satisfactory cutting result on rotation of the cylinder means 1 at a speed in the range 700-5000 rpm, more preferably in the range 1500-5000 rpm. This is due to the fact that the blades 5 are supported by blade supporting elements 4 which are arranged at a distance A from each other in the range 10-30 mm. As a result, a dimensionally stable fixing of the blades 5 is provided also at high speeds. Thus the blades are in operation subjected to radial and tangential forces which act to bend the blades outward. Such outward being is counteracted by the dimensionally stable fixing which is provided by the relatively closely arranged blade supporting elements. The outward bending is affected, not only by the rigidity of the blades and the speed, also by the length of the blades. Experiments have demonstrated that the inventive cylinder lawn mower allows use of cylinder means having a length of up to 1000 mm. Commercial cylinder lawn mowers usually have cylinder means with a length in the range 400-1000 mm, and therefore the inventive cylinder lawn mower is considered to be convenient for cylinder means with a length in the given range.

The diameter of the cylinder means may be, for example, in the range 100-250 mm. According to the present invention, the cylinder lawn mower thus comprises a cylinder means 1 , in which a number of blades 5 are supported by a plurality of blade supporting elements 4 which are arranged along a cylinder shaft 3 at a distance A from each other in the range 10-30 mm. The blades 5 have a width B1 in the range 0.5-2.5 mm. The small width B1 of the blades 5 and, where appropriate, also the abutment 4, implies that the landing areas 10, 11 which in operation are formed due to wearing, can be prevented from exceeding a threshold value, at which regrinding is required to maintain a satisfactory cutting capacity of the cylinder lawn mower. The relatively closely arranged blade supporting elements 4 provide a dimensionally stable fixing of the blades 5, which makes it possible to drive the cylinder means at a speed in the range 700-5000 rpm, more preferably in the range 1500-5000 rpm. The small width B1 of the blades 5 also allows the blades to be made in the form of curved beams, which in mounting are bent and clamped to their helical shape. The inventive cylinder lawn mower is capable of exhibiting an excellent cutting result during the entire service life of the blades and/or the abutment, and therefore the cylinder lawn mower is well suited for use as a commercial lawn mower intended for mowing of large areas, involving high demands on cutting quality. It will be appreciated that the present invention is not limited to the embodiment illustrated.

The inventive cylinder lawn mower has been described above to have blades and an abutment with a width in the range 0.5-2.5 mm. However, it falls within the scope of the invention that only one of the blades and the abutment have a width in the given range. If, for example, an abutment with a width exceeding the given range is used, a landing area will over time form along its entire end face. This will, however, have no negative effect on the cutting capacity of the cylinder lawn mower since the blades have a width which causes a restriction of the active landing area.

It is also possible to provide an inventive cylinder lawn mower with a plurality of cylinder means and associated abutments.

The inventive cylinder lawn mower can be a ride-on lawn mower. The rotation of the cylinder means can be provided by an electric motor or an internal combustion engine.

Furthermore, the invention is applicable to lawn mowers which are intended for other purposes than mowing of golf courses, lawns and the like. The lawn mower can thus be intended for agricultural purposes. A load carrier, such as a tractor, which supports one or more cylinder units, is thus according to the present invention considered to be a type of cylinder lawn mower. It will be appreciated that for this application, the dimensions, such as length and diameter, of the cylinder means can be greater than the dimensions that have been stated above. Several modifications and variations are thus conceivable, and therefore the extent of the invention is exclusively defined by the appended claims.

Claims

1. A cylinder lawn mower, comprising an engine, a fixedly arranged abutment (2) and a cylinder means (1) with at least one blade (5), said engine being arranged to rotate said cylinder means (1) about a longitudinal axis at a speed in the range 700-5000 rpm, each blade (5), by rotation of the cylinder means (1), being movable to a cutting position (K), in which the blade (5) cooperates with the abutment (2) to allow grass cutting, c h a r a c t e r i s e d in that the at least one blade (5) is supported by a cylinder shaft (3), which is extended along said longitudinal axis, via a plurality of blade supporting elements (4) which are distributed along said cylinder shaft (3) at a distance (A) from each other in the range 10-30 mm, each blade (5) having a width (B1) in the range 0.5-2.5 mm.

2. A cylinder lawn mower as claimed in claim 1 , in which said abutment (2) has a width (B2) in the range 0.5-2.5 mm.

3. A cylinder lawn mower as claimed in claim 1 or 2, in which the at least one blade (5) is arranged to make slight contact with the abutment (2) when passing the cutting position (K).

4. A cylinder lawn mower as claimed in any one of claims 1-3, in which said blade supporting elements (4) are formed with recesses which receive said blades (5)

5. A cylinder lawn mower as claimed in claim 4, in which each blade

(5) is designed in the shape of a curved beam and is clamped in said recess

(6) to obtain a helical extent of said blade (5).

6. A cylinder lawn mower as claimed in claim 4 or 5, in which each blade (5) forms a friction joint (7) with an associated recess (6) of the respective blade supporting elements (4).

7. A cylinder lawn mower as claimed in any one of the preceding claims, in which said blade supporting elements (4) are fixedly connected to the cylinder shaft (3).

8. A cylinder lawn mower as claimed in any one of the preceding claims, in which each blade supporting element (4) is a disc.

9. A cylinder lawn mower as claimed in any one of the preceding claims, in which the blades (5) are made of a highly abrasion-resistant material, such as the steel quality Docol^® M, which is sold by SSAB.

10. A cylinder lawn mower as claimed in any one of the preceding claims, in which the blades (5) are fixedly mounted on the cylinder means (1).

11. A cylinder lawn mower as claimed in any one of the preceding claims, in which the cylinder means has a length in the range 400-1000 mm.

12. A cylinder lawn mower as claimed in any one of the preceding claims, wherein the cylinder lawn mower is a ride-on lawn mower.

13. A cylinder lawn mower as claimed in any one of the preceding claims, wherein the cylinder lawn mower comprises a plurality of cylinder means (1) and associated abutments (2).