GB2077563A - Lawn mowers - Google Patents

Abstract

A lawn mower comprises a cutter assembly 14 rotatable about a horizontal axis and including cutting means which define during rotation of the assembly a cylindrical cutting zone. The assembly is driven at such a speed that the cutting means cut the grass by velocity effects, without a ledger blade. The cutting means can comprise rows of spaced tines 20. <IMAGE>

Description

SPECIFICATION Lawn mowers The present invention relates to lawn mowers.

Conventional lawn mowers can generally be categorised into two types, that is cylinder mowers and rotary mowers. Cylinder mowers comprise a plurality of helical blades which rotate about a horizontal axis and co-operate with a fixed blade or anvil to cut the grass. When properly adjusted and sharpened, a cylinder mower will give a very good cut.

However, in a cylinder mower the blades do tend to come out of adjustment after a few weeks use and a certain degree of skill is required to adjust the blades; further, the rotating blades are easily damaged by stones and other hard objects.

Rotary mowers comprise a blade rotated at a high speed about a vertical axis. The finish produced by a rotary mower is markedly inferior to that produced by a properly adjusted cylinder mower although it can be better than the finish produced by a cylinder mower with its blades out of adjustment. The blade of a rotary mower does not require adjustment and a rotary mower can be used on relatively uneven ground.

According to the invention, there is provided a lawn mower comprising a cutter assembly rotatable about a substantially horizontal axis, said cutter assembly including cutting means defining during rotation of the assembly a cylindrical cutting zone centred about the axis of the assembly and extending substantially the entire length of the assembly, and driving motor means for driving the assembly at such a speed that the assembly can cut grass without co-operation with a stationary anvil.

Further according to the invention, there is provided a lawn mower comprising a cutter assembly rotatable about a substantially horizontal axis, the cutter assembly comprising a plurality of rows of closely-spaced tines projecting transversely of the axis of the assembly, each said row of tines extending substantially axially of the assembly and the tips of the tines lying on an imaginary cylindrical surface surrounding the axis of the assembly, and drive means for rotating the cutter assembly at such a speed that the rows of tines cut the grass due to their velocity.

Still further according to the invention, there is provided a lawn mower comprising a cutter assembly rotatable about a substantially horizontal axis, said cutter assembly including cutting means extending generally axially of the assembly and defining a cylindrical cutting zone during rotation of the assembly, said cutting zone being free from contact with any other part of the mower, and means for driving the assembly at such a speed that the velocity of the cutting means at said cutting zone is sifficient to cause the cutting means to cut the grass.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a schematic perspective view of a lawn mower in accordance with the invention; Figure 2 shows to an enlarged scale one ofthe tines which forms the cutting edge of the lawn mower of Fig. 1; Figure 3 is a schematic section showing the front end portion of the mower; Figure 4 shows a modified form of tine; Figure 5 shows a further modified form of tine which enables the mower also to be used as lawn scarifier; Figures 6 to 8 show further modified forms of tine assembly.

The lawn mower shown with reference to Figs. 1 to 3 comprises a body 2 which houses an electric motor (not shown). The body is supported from the ground by wheels or rollers 4 at the back of the body and by wheels or rollers 6 at the front of the body. If the machine is to be a self-propelled machine, the wheels or rollers 4 at the back of the body can be driven by the motor through a suitable transmission system. The rollers 6 at the front of the body are adjustably mounted relative to the body to enable the height of the body relative to the ground, and therefore the height of cut, to be adjusted.The adjustable mounting of the rollers 6 on the body 2 can be effected in any suitable way and, in the embodiment shown, this achieved by mounting the rollers on a sub-assembly which is pivotally mounted on the body 2 to enable the rollers 6 to be swung about a horizontal axis between raised and lowered positions, the sub-assembly being fastened in its selected angular position for example by means of screws and wing nuts, 10, 12 in order to provide the required height of cut.

The cutter assembly 14 of the mower is mounted in the forward part of the body 2 for rotation about a substantially horizontal axis, the cutter assembly being driven by the motor housed within the body 2 through a suitable transmission. The cutter assembly comprises a central horizontal shaft 16 which supports, by means of axially spaced lugs 18, a pair of rods which extend axially along opposite sides of the shaft 16 and follow a helical path centred on the axis of the shaft. The helical path is of very large pitch and each rod will traverse only about one half of a single turn of the helix. Each rod carries a set of closely-spaced tines 20 one of which is shown in greater detail in Figure 2. As shown, the axis of the cutter assembly is perpendicular to the fore-aft axis of the machine, although in modified arrangements, it may be inclined to the fore-aft axis.

With reference to Figure 2, the tine 20 comprises a length of metal rod, the proximate end of which is bent round to form a loop by which the tine is pivotally mounted on the helical rod which is shown at 22 in Figure 2. At its distal end, the tine is angled by a few degrees in the direction of rotation as indicated in Figure 2, although the tine may alternatively be straight.In a practical embodiment, the tines may each be made of steel rod approximately 1 mm in The drawing(s) originally filed was/were informal and the print here reproduced is taken from a later filed formal copy. diameter The tines 20 mounted on each helical rod 22 are in closely spaced relationship with each tine 20 being separated from the tine adjacent thereto by means of a suitable spacer provided on the rod 22 and which could be formed by bending the proxi mate end of the tine through more than one com plete turn. In a practical embodiment with tines of 1 mm diameter, there are 2 tines per cm length of the helical rod 22.The tines 20 mounted on one of the rods 22 are axially offset with respect to those mounted on the other rod 22 so that in each set of tines, the individual tines lie opposite the gap between the opposing two adjacent tines of the other set. Thus, when the cutter assembly is rotated, the two sets of tines will, in effect, define a cylindrical cutting zone extending from one end ofthe assembly to the other and which will act to cut grass lying within that zone.

The tines 20 are freely pivotally mounted by their proximate ends on the rods 22 and when the cutting assembly is rotated at high speed by the motor, for example, a speed of between 8,000 and 10,000 rpm with a cutter assembly diameter of about form, the tines will extend radially outwardly from the shaft and cut the grass. Although in this mode the two sets of tines collectively resemble the opposed helical blades in the cutting cylinder of a cylinder mower, unlike in a cylinder mower the tines do notco- operate with a stationary cutting edge or anvil, but instead cut the grass due to their high velocity. If any of the tines encounter a stone or other hard object, they will simply swivel about the rod on which they are mounted.The tines are not sharp in the conventional sense and therefore do not become blunted in use.

In practice it has been found that the finish produced by the cutter assembly described is marginally inferior to that produced by a perfectly adjusted cylinder mower, but considerably better than that of a poorly adjusted cylinder mower or a sharp rotary mower. The finish provided by the cutter assembly described does not detiorate in use as no sharpening or adjustment is needed.

The rear half of the cutter assembly is surrounded by a part-cylindrical shield 24 (Figure 3) which forms part of the body of the machine. The adjacent part of the cutter assembly moves upwardly relative to this part cylindrical shield and therefore this shield has the effect of causing the grass cuttings to the deflected upwardly to be ejected forwardly at the top edge of the shield for collection in a suitable opentopped grass box (not shown) carried at the front of the machine as is well known in conventional cylinder mowers. As illustrated in Figure 3, a movable part cylindrical shield 26 shown in broken lines may enclose the forward part of the cutter assembly.

When so enclosed, the grass cuttings will not be projected forwardly but will instead be retained within the zone of action ofthe cutter assembly and will be chopped into very small pieces to be subsequently deposited on the ground at the bottom of the cutter assembly for mulching. With the front shield in position the machine can also effectively chop fallen leaves and fallen apples and the like. As illustrated in Figure 3, the front shield may be pivotally mounted at its upper edge on the machine body to be pivotal between its operative position in which it encloses the front part of the cutter assembly and an inoperative position in which the front part of the cutter assembly is exposed to effect ejection of the grass cuttings into the grass box.

The modified form of tine shown in Figure 4 has a flattened end 28 which is enlarged in the axial dirnc:.

tion of the cutter assembly and tends to reduce the gap between the distal ends of adjacent tines. The ends of the tines formed in this way tend to resemble more closely a cutting blade and a cutter assembly formed from such tines does tend to have an even better cutting action than that formed by tines without the flattened end.

In Figure 5, there is shown a tine 30 in which the proximate end is bent round the rod 22 and termines in a portion 32 projecting transversely from the rod: This projecting portion 32 bears against the central shaft 16 of the cutter assembly and tends to hold the tine in its operative position in contrast to the tines of the preceding embodiments which are held in their operative position by the centrifugal force during rotation of the cutter assembly.

A cutter assembly having tines of the construction shown in Figure 5 in which pivotal movement of the tines is prevented can be used also for scarifying a lawn for removing moss, dead grass, and other debris from the lawn. When used in a scarifying mode, the cutter assembly will be rotated at a substantially slower speed than that used during cutting (for example from 2,000 to 2,500 rpm when scarifying, and 8,000 to 10,000 rpm when cutting as discussed earlier) and to permit this reduction in speed, the motor can be provided with a two-speed control to provide a high speed for cutting and a low speed for scarifying or a two-speed transmission can be incorporated between the motor and the cutter assembly.

In addition, when used for scarifying the cutter assembly will be set lower than when cutting so that the tines can engage the ground; this adjustment is effected by means of the wheels or rollers 6 at the front of the machine.

Although tines of the construction shown in Figure 5 cannot freely pivot when contacting a stone or other obstruction in the grass, the bent proximate end portion of the tine acts as a helical spring which will enable the- main portion of the tine to flex if it does encounter a stone or the like thus avoiding damage to the tine.

Machines for scarifying lawns and comprising an array of rotatable tines are known. However, these known machines differ from the machine described above in that the known machines comprise tines which are relatively widely spaced in an axial direc- tion and the speed of the tine assembly is sufficient to effect scarifying but insufficient to effect cutting even if the speed were sufficient cutting could not effectively occur because of the wide spacing of the tines. Finally, scarifying machines do not have a range of height adjustment which would be compatable with a cutting action.

Modified forms of cutter assembly are shown purely schematically in Figures 6to 8. In Figure 6 the cutter assembly is formed by rows of flat strips 34 having ends bent in the direction of rotation. The rows of strips are equally-angularly offset and the strips of each row are axially offset with respect to those of the other rows. The strips may be resilient and rigidly mounted on the central shaft or may be pivotally mounted on rods in a manner similar to that of the tines of Figures 1 to 3. In Figure 7 the cutter assembly comprises rows of axially-spaced wire hoops 36, the rows being equally-angularly offset with the hoops of the respective rows being axially offset to that each hoop faces the gap between two adjacent hoops in the other row of hoops.The hoops may be resilient and rigidly mounted on the central shaft or may be pivotally mounted on rods in the manner of the tines of Figures 1 to 3. Figure 8 shows a modification of the arrangement shown in Figure 7 in which tines 38 are placed in the gaps between adjacent hoops 36 of each row.

In each of the foregoing embodiments, each row of tines or other cutting members may be arranged to extend helically within the cutter assembly (as described for the tines of Figures 1 to 3) or may extend rectilinearly within the cutter assembly, a helical arrangement being preferred as it provides a continuous cutting action. There may be two, three, four or more rows equi-angularly spaced around the axis of the central shaft so that the assembly is in balance.

In the cutter assembly particularly described, the tines or other cutting members in the respective rows cooperate to define a during rotation of the assembly a substantially uninterrupted cylindrical cutting zone centred about the axis of the assembly and extending the entire length of the assembly. The cutter assembly rotates at such a speed that the cutting members cut the grass without co-operating with a stationary cutting blade or anvil. Typically, for a cutter assembly having a diameter of 1 Ocm, the assembly would be rotated at between 8,000 and 10,000 rpm although cutting can occur at speeds down to about 5,000 rpm. In contrast in a conventional cylinder mower with a cutting cylinder of the same size, the cylinder which cuts by co-operation with a stationary blade or anvil rotates at about 2,000 to 2,500 rpm.

In comparison with conventional cylinder mowers, the mower particularly described produces a finish which is almost as good as that produced with a perfectly adjusted cylinder mower and considerably better than that produced by a cylinder mower which has gone out of adjustment (which is nearly always the case in practice), but the quality of finish does not deteriorate with use. The finish is markedly superior to that produced by a rotary mower, even rotary mower with a sharp blade, but, like a conventional rotary mower, the lawn mower particularly described can cope effectively with wet grass and with uneven ground. The grass collecting characteristics of the lawn mower particularly described are better than those in conventional rotary mowers where this facility is provided. Tests carried out with a cutter assembly composed of pivotal tines have shown that the likelihood of serious injury occurring to the hands and feet in an accident involving the machine are far less that that with a conventional rotary mower.

Although as particularly described, the body of the mower is supported from the ground by wheels or rollers, the body may alternatively be supported from the ground by an air cushion acting on the hover principle.

Claims (20)

1. A lawn mower comprising a cutter assembly rotatable about a substantially horizontal axis, said cutter assembly including cutting means defining during rotation ofthe assembly a cylindrical cutting zone centred about the axis of the assembly and extending substantially the entire length of the assembly, and driving motor means for driving the assembly at such a speed that the assembly can cut grass without co-operation with a stationary anvil.

2. A lawn mower according to claim 1, wherein the cutting zone is defined by at least one row of axially spaced cutting members.

3. A lawn mower according to claim 2, wherein there are at least two rows of axially spaced cutting members, the rows being angularly offset about the axis of the assembly.

4. A lawn mower according to claim 3, wherein the respective cutting members of one row are aligned with gaps between adjacent cutting members of a second row.

5. A lawn mower according to any one of claims 2 to 4, wherein the cutting members comprise tines which extend transversely to the axis of the cutting assembly.

6. A lawn mower according to any one of claims 2 to 5, wherein the cutting members are pivotally mounted in the cutter assembly so that the cutting members project transversely with respect to the axis of the cutter assembly when the cutter assembly is rotated.

7. A lawn mower according to any one of claims 1 to 6, comprising deflector means for deflecting grass cuttings from the cutter assembly into a grass box carried by the machine.

8. A lawn mower according to claim 7, wherein the deflector means comprises a part-cylindrical shield surrounding part of the circumference of the cutter assembly.

9. A lawn mower according to claim 8, further comprising a second part-cylindrical shield which can optionally be placed in a position to surround another part of the circumference of the cutter assembly to prevent the ejection of grass cuttings whereby said grass cuttings are finely divided by the cutter assembly to be subsequently deposited on the ground beneath the cutter assembly.

10. A lawn mower comprising a cutter assembly rotatable about a substantially horizontal axis, the cutter assembly comprising a plurality of rows of closely-spaced tines projecting transversely of the axis of the assembly, each said row of tines extending substantially axially of the assembly and the tips of the tines lying on an imaginary cylindrical surface surrounding the axis of the assembly, and drive means for rotating the cutter assembly as such a speed that the rows of tines cut the grass due to their velocity.

11. A lawn mower according to claim 10, wherein the respective tines of each row are axially offset with respect to those of an adjacent row such that the respective tines of one row face the gaps between adjacent tines of said other row.

12. A lawn mower according to claim 10 or claim 11, wherein the ends ofthe tines are flattened and enlarged axially of the cutter assembly.

13. A lawn mower according to any one of claims lotto 12, wherein each row of tines extends helically of the assembly.

14. A lawn mower according to any one of claims 10 to 13, wherein the tines are freely pivotally mounted in the cutter assembly so as to project transversely outwardly of the assembly during rotation thereof.

15. A lawn mower according to any one of claims 10 to 13, wherein the tines are held by spring mounting means in a position which they extend transversely to the cutter assembly.

16. A lawn mower according to claim 15, comprising selectively operable control means for causing the cutter assembly to be driven at a slower speed at which cutting will not occur, and means for lowering the height of the cutter assembly relative to the ground such that when the cutter assembly is driven at the slower speed and is lowered relative to the ground, the cutter assembly will act as a scarifier.

17. A lawn mower according to any one of claims 10 to 16, further comprising a part-cylindrical shield surrounding the upwardly moving part of the rotating cutter assembly to deflect grass cuttings and other debris upwardly into a grass box.

18. A lawn mower according to claim 17, further comprising a movable part-cylindrical shield arranged to surround the downwardly moving part of the rotating cutter assembly, said movable shield preventing the ejection of debris from the upper part of the first mentioned shield whereby the debris will be retained within the zone of action of the cutter assembly to be chopped into small pieces for mulching purposes.

19. A lawn mower comprising a cutter assembly rotatable about a substantially horizontal axis, said cutter assembly including cutting means extending generally axially of the assembly and defining a cylindircal cutting zone during rotation of the assembly, said cutting zone being free from contact with any other part of the mower, and means for driving the assembly at such a speed that the velocity of the cutting means at said cutting zone is sufficient to cause the cutting means to cut the grass.

20. A lawn mower substantially as herein described with reference to the accompanying drawings.