ROTARY LAWN MOWER AND ROTARY UNIT THEREFOR

Abstract: A lawn mower comprising a body (2), a cutting unit including a motor (3) and rotors (4-6) which are rotatably mounted in said body (2), each about its essentially vertical shaft and being driven by the motor (3), and wheels (7a, 7b, 8a, 8b) for supporting said body (2). At least one of the rotors (4, 5) forms a rotary unit together with one of the wheels (7a, 7b) that is mounted centrally underneath the rotor (4, 5). The rotational axis (12) of the wheel (7a, 7b) of each rotary unit forms an acute angle ( omega ) with the rotational axis (13) of the rotor (4, 5).

Description: ROTARY LAWN MOWER AND ROTARY UNIT THERETO Technical Field The present invention relates to a lawn mower and more particularly to a rotary lawn mower provided with mower-supporting wheels arranged centrally underneath one or a number of its rotors. The invention also concerns a rotary unit for lawn mowers, which rotary unit comprises a rotor and a wheel disposed centrally under ¬ neath the rotor to support the rotary unit. Technical Background The wheels of a rotary lawn mower typically are disposed externally of a body which in turn encloses the rotors. Consequently, the wheels normally are disposed externally of the total cutting width of the rotors. This means that as the lawn mower advances, its wheels will press down uncut grass, which affects the cutting results negatively, since the uncut grass normally will not have time to reassume its upright position before the lawn mower is again driven across the earlier affected but not yet cut stretch of the lawn. In addition, the cutting results become dependent on the current conditions of the lawn. For example, the lawn surface is commonly partly covered by loose objects, such as leaves or small twigs. In order to mow such a lawn the lawn mower wheels must first be passed across the objects, which are then impacted by the rotor. This means that the objects are smashed into pieces by the rotating rotor as the grass underneath the objects is being cut. The rotor therefore will change its position from a plane wherein it is parallel with the plane of the ground to a plane wherein it is inclined relative to the plane of the ground, should a wheel move on top for instance of a twig. The stretch of the lawn covered at that moment by the rotor thus will be cut with the rotor assuming a position in said oblique plane. It is likewise common for a lawn not to be entirely even. Should minor protrusion therein happen to be positioned within the lawn mower wheel base, the grass on said protrusion will be cut to a lower height than the set cutting height. Should, in addition, the extension of the protrusion vertically be sufficiently large the rotor will come into contact with the ground on top of the protrusion, with resulting damages to the lawn and considerable wear on the rotor blades. A further problem encountered in conventional lawn mowers is that they do not allow the edges of the lawn adjacent for instance flower-beds to be cut because of the lawn mower wheels being mounted externally of the rotor . These problems may be solved by mounting a wheel centrally below some of the lawn mower rotors and mounting the rest of the wheels behind these rotors. In accordance with this arrangement it is important that no wheel will be positioned externally of the total cutting width of the rotors at any one time during the advancement of the lawn mower in order to ensure satisfactory cutting results . During the advancement of this lawn mower a front part of a rotor could then first be passed over an uncut stretch of the lawn, the rotor then ensuring that the stretch is cleared of loose objects. Then, the rotor wheel reaches the stretch in question, for which reason there is no risk that the rotor will assume an oblique position as the wheel passes across that stretch. In addition, the wheels always pass across an already cut stretch of the lawn, which further improves the cutting results, since that stretch will be more even than it would have been, had it been uncut. The fact that the rotor is supported by a wheel disposed in its centre allows the rotor to follow the outline of the lawn more closely. Accordingly, the risks of varying cutting heights and contact between the rotor and the ground as the lawn mower is moved across an uneven lawn are greatly reduced. Finally, an overhang is produced as regards the lawn mower rotors owing to the mounting of the wheels central- ly below the rotors. Such overhang makes it possible to cut lawn edges adjacent flower beds. However, this type of lawn mower suffers from a considerable drawback, viz. that the mounting of a wheel centrally below a rotor gives the rotor a considerable extent vertically. More precisely, the rotor must be configured as a dish the depth of which is determined by the wheel diameter. From the large vertical extent of the rotor follows large dimensions in the lawn mower itself. The large dimensions, and particularly at the front of the lawn mower, make it difficult for the lawn mower to reach in underneath shrubs, fences and the like. In addition, the lawn mower may be difficult to operate because of its size. A further disadvantage inherent in wheels mounted underneath the rotors is that the drive of the mower by means of these wheels requires the use of a complicated type of transmission. A first object of the present invention thus is to provide a lawn mower which is capable of cutting grass to the same quality as the above-described lawn mower while at the same time it is compact and easy to handle. By 'compact' is intended in the present case a lawn mower by means of which cutting operations underneath for instance shrubbery are easily performed. A second object of the invention is to also design the lawn mower in such a manner that no complex transmission is required for the drive of the mower. Summary of the Invention The first object is achieved by means of lawn mower possessing the characteristics defined in claim 1, as also by means of a rotary unit possessing the characteristics defined in claim 12. Preferred embodiments by means of which also the second object is achieved appear from the dependent claims . More precisely the invention provides a lawn mower comprising a body, wheels for supporting said body, and a cutting unit including a motor and rotors with cutting blades thereon, each one of said rotors being rotatably mounted in the body for rotation about its individual, essentially vertical shaft and being driven by said motor, at least one of said rotors forming a rotary unit together with one of said wheels, which wheel is mounted centrally below its associated rotor, and this lawn mower is characterised in that the rotational axis of the wheel of each rotary unit forms an acute angle with the rotational axis of the rotor (or, which is equivalent, with a line m parallel with the rotational axis of the rotor) . By mounting the wheels centrally below the rotors the wheels will not affect the cutting result since they cannot press down uncut grass during the advancement of the lawn mower. If the wheels not forming part of the rotary units are arranged behind the rotary units or m any other way within and rearwardly of the total cutting width the of the rotors, cutting results equalling those achieved by the prior-art lawn mower type discussed above are achieved. Because the rotational axis of the wheel of each rotary unit forms an acute angle with the rotational axis of the rotor, i.e. because of the oblique orientation of the wheel of each rotary unit, the rotors of each rotary unit may be configured to a less deep dish shape compared with that of the above-described lawn mower type, and consequently the vertical extent of the lawn mower may be reduced, resulting m a more compact lawn mower. In accordance with a preferred embodiment the rotational axis of the wheel of each rotary unit has a fixed position in a vertical plane transversely of the mower cutting direction, whereby the tangents of said wheels become parallel to the cutting direction at the points of wheel contact with the plane of the ground. In accordance with a second embodiment the rotational axes of the wheels of the rotary units are arrang- ed to be shifted between two fixed positions in a vertical plane transversely of the mower cutting direction, it thus being possible to optionally arrange the points of contact of these wheels with ground according to choice on one or the other side of the rotational axis of the associated rotor, as seen in the cutting direction. In the case of a lawn mower comprising two front rotors arranged in juxtaposed position and each forming a rotary unit, and one rear rotor which is disposed intermediate the two front rotors and in overlapping relation- ship therewith as seen in the cutting direction, the shiftability feature allowing the wheels of the rotary units to be set in different positions provides the advantage of making it possible to displace the points of contact of these front wheels with ground inwardly, towards the centre of the mower or outwards, towards the sides thereof. When the points of contact are moved inwards, the overhang of the rotors of the rotary units towards the lawn mower sides increases, which is an advantage when the mower is used to cut the edges of the lawn adjacent for instance flower-beds. When the wheel of a rotary unit is set for maximum overhang, the resulting overhang exceeds that of the prior-art lawn mower comprising wheels that are disposed centrally underneath a rotor, which obviously is due to the fact that the point of contact with ground in the case of a wheel of a rotary unit in the prior-art lawn mower type always is positioned straight underneath the rotational axis of its rotor. This limits the overhang to half the size of the rotor diameter. In the rotary unit in accordance with the present invention the rotor may form a larger overhang when the point of contact of the wheel with ground is displaced past the rotational axis of the rotor, inwards towards the centre of the mower. On the other hand, when the points of contact are moved outwards, towards the sides of the lawn mower a more steadily supported mower is obtained. In accordance with a third embodiment, the rotational axes of the wheels of the rotary units are variably rotatable while retaining their angular orientation about the rotational axis of their associated rotor. According to this embodiment the wheels of each rotary unit may adjust themselves into a suitable position as the lawn mower is being advanced and also change their orientation, should the direction of advancement of the lawn mower be changed, which facilitates such a change of direction. In accordance with one alternative, for the propulsion of the lawn mower the wheels of the rotors are arranged to drive the mower forwards. Power is drawn from the lawn mower motor and is transferred to the wheels in question via a suitable transmission, which may be of a simple nature owing to the inventive rotary unit structure . In accordance with a further embodiment of the invention the lawn mower is adapted to support and transport the operator of the mower. Brief Description of the Drawings Fig. 1 is a view from above of a lawn mower according to the present invention. Fig. 2 is a cross-sectional view along line II-II in Fig. 1 of a wheel forming part of a rotary unit in a lawn mower according to the present invention. Fig. 3 is a view from above of a travelling self- propelling lawn mower according to one embodiment of the invention. Description of Preferred Embodiments The lawn mower 1 according to the present invention illustrated in Fig. 1 comprises a body 2, a cutting unit including a motor 3 and three rotors 4-6, four wheels 7a, 7b, 8a, 8b, and a handle bar 9. The two rotors 4, 5 are rotatably mounted in juxtaposed positions and are mounted in the body 2, and a third rotor 6 is rotatably mounted in the body 2 behind and intermediate the two front rotors 4, 5 and in overlapping relationship thereto. The body 2 encloses the three rotors 4, 5, 6. The two wheels 8a, 8b are mounted on the body 2 behind the two front rotors 4, 5, one on either side of the rear rotor 6 but interiorly of the lateral boundaries of the total cutting width 10 of the rotors 4, 5, 6. The two wheels 7a, 7b are mounted in the centres of the two front rotors 4 and 5, respectively. The rotational axes of the wheels 7a, 7b are at an acute angle relative to the rotational axes of the rotors 4 and 5, respectively, in a fixed position in the vertical plane transversely of the cutting direction. Finally, the handle bar 9 is mounted on the body 2 and extends in a direction upwards-rearwards relative to the cutting direction. Fig. 2 illustrates a rotary unit 11 wherein the rotational axis 12 of the wheel 7b of the rotor 5 is at an acute angle φ to the rotational axis 13 of the rotor 5. In addition to the rotor 5 including the blades 14 associated therewith and the wheel 7b with its associated shaft 15, the rotary unit 11 also comprises a bearing bushing 16 and a pulley 17. The rotor 4 and the wheel 7a form another rotary unit similar to the rotary unit 11. One end of the bearing bushing 16 has a flange 18 by means of which the bushing 16 may be mounted in an aperture 19 in the body 2. For instance a screw fastener 20 and a fastening hole 21 formed in the rotor-enclosing body 2 may be used to fix the angular position of the bearing bushing 16 relative to the body 2. A locking ring 22 in threaded engagement with the opposite end of the bearing bushing 16 and a spacer sleeve 23 enclosing the middle portion of the bearing bushing 16 securely mount the bearing bushing 16 to the body. The pulley 17 and the rotor 5 are disposed concentrically on the bearing bushing 16 so as to rotate about the spacer sleeve 23 and the bearing bushing 16. An end-to-end bore 24 is formed in the bearing bushing 16 for reception therein of the shaft 15 of the wheel 7b. The wheel 7b has a bevelled edge 25 and is rotatably mounted at one end 26 of the shaft 15. The upper part of the wheel shaft 15 is formed with a number of through holes 27a-d disposed in superposed position. Another hole (not shown) is formed in the bearing bushing 16. By insertion of a cotter pin into said hole in the bearing bushing 16 and further through a chosen one of the holes 27a-d in the wheel shaft 15 the level of the rotor blades 14 above ground may be adjusted. In the embodiment of Fig. 2 the centre line of the bore 24 forms an angle φ which may be approximately 15° to the vertical. The centre line of the bore 24 also extends in a vertical plane which is perpendicular to the cutting direction of the lawn mower 1, i.e. a vertical plane through line II in Fig. 1. As a result of this angular disposition the wheel 7b assumes an oblique position relative to the plane of the ground and the bevelled edge 25 of the wheel 7b becomes parallel with the ground at the point of contact between the wheel 7b and the ground. As a lawn mower 1 in accordance with Figs 1 and 2 advances, its wheels 7a, 7b disposed in the rotors 4, 5 will rotate about their respective shafts 15 and together with the other wheels 8a, 8b support the mower 1 in a stable manner. Because of the oblique orientation of the wheels 7a, 7b the depth of the dish-shaped configuration of the rotors 4, 5 may be reduced, resulting in a compact mower 1 by means of which also surfaces difficult of access, such as surfaces underneath bushes, fences and the like, may be cut. Fig. 3 illustrates a travelling and self-propelling lawn mower in accordance with a second embodiment of the present invention. The embodiment comprises a cutting unit 28 similar to the one in the lawn mower of Fig. 1. The cutting unit 28 is mounted in the front part of a body 29 which comprises a seat 30 and a hand-wheel 31 and which is supported by four wheels 32a, 32b, 33a, 33b. The lawn mower in accordance with this embodiment is adapted to support and transport a user who operates the lawn mower by means of the hand-wheel 31. For this reason one pair of wheels 32a, 32b is adapted to drive the travelling lawn mower whereas a second pair of wheels 33a, 33b may be steered by means of the hand-wheel 31. As described with reference to Fig. 1 also the cut- ting unit 28 comprises four wheels 34a, 34b, 35a, 35b. Because the cutting unit is supported by these wheels 34a, 34b, 35a, 35b the cutting unit may be hingedly connected with the body 29 about an axis 36 extending in parallel with the level of the ground and at right angles to the longitudinal direction of the mower. In order to ensure satisfactory cutting results all wheels 32a, 32b, 33a, 33b, 34a, 34b which are not disposed in a rotary unit should be placed behind and interiorly of the total cutting width of the cutting unit 28 in conformity with the above. It should be appreciated that the present invention is not limited to the embodiment described above. It is within the scope of the invention to arrange for the wheels disposed in the rotors 4, 5 as driving wheels in order to produce a self-propelling lawn mower. Obviously, the motor 3 is used to effect the drive and the transmission could be e.g. a belt transmission, a gear transmission or a hydraulic transmission. In addition, it is possible to make the rotational axes of the wheels 7a, 7b of the rotors 4, 5 adjustable, allowing them to be set in two fixed positions in the vertical plane transversely of the lawn mower cutting direction, in order to define the rotor overhang. In total four set positions are possible, i.e. a small or a large overhang on both sides of the lawn mower, a large overhang on one side and a small on the other, or reversely. A further possibility is to provide for the rotational axes of the wheels of the rotors to be rotatable about the rotational axis of the associated rotor while maintaining the angular setting relative to that axis. A condition therefor is either that the points of contact of the wheels with the ground are positioned in the prolongation of the rotational axis of the rotor or that the wheels are steerable in parallel, at least in pairs. It is not either necessary for the shaft of a wheel of a rotor to pass through the bearing bushing in a bore that extends at an angle to the vertical. Alternatively, the passage through of the bearing bushing could be in the form of a boring extending in parallel with the vertical whereas the wheel shaft could extend at an angle underneath the bearing bushing in order to obtain the rotational axis of wheel that is at an angle to the rotational axis of the rotor. It is not either necessary for the wheel to be in the form of a disc having such a bevelled edge as is illustrated in Fig. 2. For instance, the wheel may be of the kind having a rim and a tyre. The advantage of this arrangement is that the surface of contact between the wheel and the ground becomes smaller, thus reducing friction losses. It is further possible to arrange for one wheel in each one of the rotors of the lawn mower and not, as in accordance with the embodiment in the drawing figures, in the front rotors only. Finally, one or several rotary units of the kind described above could be employed in other embodiments of lawn mowers. It is thus fully conceivable to use rotary units in accordance with the invention as accessories in a vehicle, such as a tractor, the rotary units in this case preferably being mounted ahead of the front wheels of the tractor in order to ensure satisfactory cutting results . The claims attached hereto are believed to cover all changes and modifications that are within the scope of the invention.

Claims: CLAIMS 1. A lawn mower comprising a body (2), a cutting unit including a motor (3) and rotors (4-6) with cutting blades thereon, each one of said rotors being rotatably mounted in the body (2) for rotation about its individual, essentially vertical shaft and being driven by said motor (3), and wheels (7a, 7b, 8a, 8b) for supporting said body (2), at least one of said rotors (4, 5) forming a rotary unit together with one of said wheels, which wheel is mounted centrally below its associated rotor (4, 5), c h a r a c t e r i s e d in that the rotational axis (12) of the wheel of each rotary unit (4, 5) forms an acute angle (φ) with the rotational axis (13) of the rotor ( 4 , 5) . 2. A lawn mower as claimed in claim 1, c h a r a c t e r i s e d in that the rotational axis (12) of the wheel (7a, 7b) of each rotary unit has a fixed posi- tion in a vertical plane transversely of the mower cutting direction. 3. A lawn mower as claimed in claim 1, c h a r a c t e r i s e d in that the rotational axis (12) of the wheel (7a, 7b) of each rotary unit is arranged to be set in two fixed positions in a vertical plane transversely of the mower cutting direction. 4. A lawn mower as claimed in claim 1, c h a r a c t e r i s e d in that the rotational axis (12) of the wheel (7a, 7b) of each rotary unit is variably rotatable about the rotational axis (13) of the rotor (4, 5). 5. A lawn mower as claimed in any one of claims 1-4, c h a r a c t e r i s e d in that the wheel (7a, 7b) of each rotary unit has a shaft (15) extending through the body (2) at an angle (φ) relative to the rotor axis (13) of the rotor (4, 5) which is identical with said acute angle . 6. A lawn mower as claimed in any one of claims 1-4, c h a r a c t e r i s e d in that the wheel (7a, 7b) of each rotary unit is connected to a shaft extending through the body (2) in parallel with the rotational axis of the rotor (4, 5) . 7. A lawn mower as claimed in any one of claims 1-3, c h a r a c t e r i s e d in that the wheel (7a, 7b) of each rotary unit is arranged to drive the mower (1) in the cutting direction. 8. A lawn mower as claimed in any one of claims 1-7, c h a r a c t e r i s e d in that the cutting unit comprises three rotors (4-6), two (4, 5) of which are disposed side by side and in front of the third rotor (6) in an overlapping relationship as seen in the direction of cutting of said mower. 9. A lawn mower as claimed in claim 8, c h a r a c t e r i s e d in that each one of said front rotors (4, 5) forms one rotary unit. 10. A lawn mower as claimed in claim 9, c h a r - a c t e r i s e d in that the wheels (8a, 8b) not forming part of a rotary unit are disposed behind the front rotors (4, 5) and externally of the rear, third rotor (6) but within the outline of the total cutting width (10) of the rotors (4-6) . 11. A lawn mower as claimed in any one of claims 1-10, c h a r a c t e r i s e d in that the shafts (15) of the wheels (7a, 7b) forming part of the rotary units are displaceably mounted in said body (2) for adjustment of the cutting height. 12. A lawn mower as claimed in any one of the preceding claims, said mower arranged to support and transport the operator of said mower. 13. A rotary unit for lawn mowers, comprising a rotor (4; 5) with cutting blades thereon and rotatably mounted for rotation about a vertical shaft, and a wheel (7a; 7b) which is mounted centrally underneath the rotor (4; 5), c h a r a c t e r i s e d in that the rotational axis (12) of the wheel (7a; 7b) forms an acute angle (φ) with the rotational axis (13) of the rotor (4; 5) .

Inventors: FISCHIER MATS, FISCHIER, MATS
Applicants: FISCHIER MATS, MATS FISCHIER I BAASTAD AB, FISCHIER, MATS
Application year: 1997
Main classification: A01D34
IPC codes: A01D34, B60B19