GB2215176A - Lawnmower - Google Patents

Lawnmower Download PDF

Info

Publication number
GB2215176A
GB2215176A GB8803443A GB8803443A GB2215176A GB 2215176 A GB2215176 A GB 2215176A GB 8803443 A GB8803443 A GB 8803443A GB 8803443 A GB8803443 A GB 8803443A GB 2215176 A GB2215176 A GB 2215176A
Authority
GB
United Kingdom
Prior art keywords
blades
lawnmower
ride
blade
disc
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB8803443A
Other versions
GB8803443D0 (en
GB2215176B (en
Inventor
John Dixon
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Barrus EP Ltd
EP Barrus Ltd
Original Assignee
Barrus EP Ltd
EP Barrus Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Barrus EP Ltd, EP Barrus Ltd filed Critical Barrus EP Ltd
Priority to GB8803443A priority Critical patent/GB2215176B/en
Publication of GB8803443D0 publication Critical patent/GB8803443D0/en
Publication of GB2215176A publication Critical patent/GB2215176A/en
Application granted granted Critical
Publication of GB2215176B publication Critical patent/GB2215176B/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • AHUMAN NECESSITIES
    • A01AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01DHARVESTING; MOWING
    • A01D34/00Mowers; Mowing apparatus of harvesters
    • A01D34/01Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus
    • A01D34/412Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus having rotating cutters
    • A01D34/63Mowers; Mowing apparatus of harvesters characterised by features relating to the type of cutting apparatus having rotating cutters having cutters rotating about a vertical axis
    • A01D34/82Other details
    • A01D34/826Noise reduction means
    • AHUMAN NECESSITIES
    • A01AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01DHARVESTING; MOWING
    • A01D2101/00Lawn-mowers

Abstract

A substantial reduction in noise generation from a ride-on lawnmower is achieved by forming the cutter head with a central disc and protuding blades each with a forward cutting and an upwardly turned rearward edge. Because the upwardly turned rearward edges of the blades increase of the blades the effective airflow, the cutter head can be driven more slowly and thereby, other things being equal, reduce engine and transmission noise. Surprisingly, the number of protruding blades on the cutter can be increased over the conventional number, and is, typically eight blades. Thus, by a combination of blade design, number of blades, and consequential speed reduction improved acoustic performance can be achieved for the same level of grass cutting and collection. The noise reducing charateristics can be supplemented by other conventional shielding, damping, and shrounding expedients.

Description

LAWNMOWER THIS INVENTION relates to noise-reducing modifications to a ride-on lawnmower.

Techniques of noise-reduction for machinery are generally known. They include operating the rotating parts of equipment at lower power ratings and/or speeds; surrounding the engine with noise absorbent layers: damping the vibrations of any panel members with adherent damping layers modifications to shape of exhaust systems: additional skirting and shielding for engine compartments; and so. In these ways the sum total of noise, whether produced by the operation of the engine itself, by induced vibration from the engine, or by the noise of the exhaust for waste gases can be reduced.

When the engine is a component part of other equipment, then further noise reducing expedients must be brought into effect. This is particularly so for equipment to be used in a domestic or urban environment, possibly by lay users, where noise requirements are often strictly controlled by local or other regulation.

A typical example of such equipment is a ride-on lawnmower, used for example for large lawns or expanses of grass up to say 5 acres of so in a surburban or semi-rural environment.

A ride-on lawnmower of the type referred to in this document is intended for lawns, paddocks, orchards, or the like. It comprises a main frame supporting a motor, suitable drive and transmission to the ground wheels, and suitable drive and transmission to a cutter deck This usually comprises blades mounted on a vertical spindle the blades are housed within a circular hood, both for safety, and to provide, jointly with the rotation of the blades, a current of air. This is forced out, via a large aperture and through a connecting duct into a collecting bag at the rear of the machine. All the normal controls and refinements of such machinery can also be present.

NoIse suppression of such ride-on lawnmowers is not a widely investigated field. We have now, however, investigated this specific equipment and have established that a critical amount of the total noise produced is generated within the cutter deck and by the blades and the air exhaust to the grass collection.

Our invention thus sets out to provide modifications to a ride-on lawn mower affecting the speed and configuration of the cutter disc and blades attached thereto as a key feature.

In one aspect the invention consists in a ride-on lawnmower in which an engine is provided to drive a circular cutter disc to rotate about a vertical axis, said disc-carrying at least four blades in balance about the pivot and protruding from the periphery of the disc, each blade having an axially outer leading cutter edge and an axially outer trailing edge a portion of which is upwardly turned behind at least part of the cutting edge length to increase air flow and cutting performance to an extent sufficiently to offset predetermined low speed engine and cutter operation governing noise production.

There may be four, six or (in a preferred embodiment) eight such blades on the disc. However, there is no reason why odd numbers of blades on the disc e.g. 5, 7 or 9 may not be employd.Typically, they protrude by more than half their length, and are sharpened as a leading edge for about half of, or somewhat less then half of, their overall length.

The upwardly turned trailing edge is usually shorter than the cutting edge, e.g. about half of its length (say 30 - 70%, more especially 40 - 60%). It is typically turned up to an extent, viewed from the cutting edge, of about half the width of the blade.

Preferably, it occupies an angle of say 400 - 600 e.g. 450 to the plane of the blade itself.

A typical overall diameter between blade tips is from 50 - 100 cm e.g. 75 cm with for instance blades of 15 cm protrusion on a 45cm disc.

Such a disc, with preferably eight blades is optionally rotated at say 1500 -2000 r.p.m. e.g. 1700 1800 r.p.m. This can be effected by a engine operating at 2500 - 3000 r.p.m. and suitable pulley ratios, preferably themselves somewhat lower e.g. 1.3 - 1.5 or specifically 1.4 than the customary 1.7 or so.

As discussed in more detail below, the expected increase in noise due to use of more blades (i.e.

eight), of more marked configuration, can be acoustica'ly offset by the unexpectedly low rotary speed (and engine speed) at which adequate cutting and gas flow transfer of cut material still takes place.

Also as described below ancillary features cf sound reduction in the cutter deck, air duct, engine and engine exhaust can also be incorporated.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 shows diagrammatically the layout of the major features of a ride-on lawnmower; Figure 2 shows from above a cutter-blade suitable for use with such a lawnmower as part of an overall noise reducing design system: Figure 3 is an end view of the blade shown in Figure 2; Figure 4 is a front view of such a blade, i.e.

looking at the cutting or leading edge: Figure 5 is a graph of air-flow from a cutter deck, equipped with different blade systems generating different air flows versus weight of grass collected from said air flow; Figure 6 is a graph of noise versus air flow, at constant blade speed but with different types of blade design generating different air flows; Figure 7 is a graph of noise versus air flow, at constant blade speed but with different numbers of blades generating different air flows; Figure 8 is a graph of noise versus air flow, with the blade as shown in Figure 2 at different speeds generating different air flows; Figure 9 is a diagrammatic graph showing the combined effect of the noise-affecting features of Figures 6, 7 and 8; Figure 10 shows diagrammatically from below a re-design of the underside of the cutter deck housing:: Figure 11 shows in section a redesign of the interconnection between the cutter-deck air exhaust and a duct leading to a grass-collection chamber; and Figure 12 shows diagrammatically a section through the mounting of an engine-compartment noise-shielding panel.

The ride-on lawnmower shown in Figure 1 is not intended to be an accurate representation of any existing model, but to show the general relative layout of the major features of front-engined equipment.

Needless to say, the invention canalso be applied to rear-engined equipment.

The mower comprises a tractor unit with engine 1 in conventional housing 2 supported on ground-engaging driven wheels 3 and steerable wheels 4. An operator seat 5, footrests 6,and conventional controls e.g. at 7, 8 are also provided. Beneath the tractor, between the front and back axles, is a cutter deck 9 with a downwardly open dished cover 10 through the centre of which passes vertical shaft 11, driven the by motor 1, and supporting a horizontal circular disc and a number of blades protuding from the edge thereof.

These latter features are not shown in Figure 1 but shown in detail in Figures 2, 3 and 4.

The motor further comprises a grass-collecting unit 12; comprising a chamber 13 in the form of a sack or rigid perforate polymer box, an arcuate polymeric duct 14 of a general "banana-shape" configuration, and a tangential air cfftake 15, connected to the top of the cover 10 towards the outer edge thereof. The duct or guide can possess a three-sided open configuration if desired. Air-flow entering around the periphery of the cover 10 entrains grass cut by the blades and passes, via 15, into duct 14 and air-collection chamber 12.

It is to be noted that in some climates grass grows sparsely, but is dry and easy to cut. Often, in these circumstances, no grass-collection is made, the relatively small amount of cuttings not being unsightly as it dies and decomposes back into the soil. Other climates are moister, with lusher growth, and necessitate pickup of grass. These climates are more testing for mower design. The present invention is intended to cover the use of the mower whether or not the grass-collection chamber is fitted.

Figures 2, 3 and 4 can be considered jointly as showing an improved blade design and its fitment to a cutter disc.

Blade 20 is based on an elongate generally rectangular shape, bolted at 21, 22 to the underside of a disc 23 (the edge position of which is shown in a dotted line).

Disc 23 (nor otherwise shown) s generally conventional typically being slightly dished upwards at its outermost periphery radially beyond bolt 22, and possessing a circular upwardly deformed strenthening rib radially within bolt 21, to surround and define a central region for attachment to a rotary hub. A typical disc diameter is about 45 cm.

Blade 20 is rounded off at its radially inner end 24, sharpened along the radially outer part of one long edge to define a leading edge 25 and so configured along the corresponding radially outer part of the other long edge as to present first a part-circular recess 26 and secondly an upwardly bent end portion 27, extending at an angle of typically 400-600 e.g. 450 to the flat of the blade. The radially inner part of the blade, comprising the two bolt-holes 21 and 22, is itself slightly dished upwardly at 28 for strength, to possess raised sides 29, 30 and raised end 31. A typical blade length is about 25cms, with say 15 cms projection from the edge of the disc 23.

Typically, eight such blades 20 are provided on the disc 23, arranged symmetrically about the axis of rotation. Six, or four blades, or possibly an odd number of blades, can also be used. More blades than 8 are less preferred, but possible.

The use of a relatively high number of such blades with a high degree of twist is generally counterindicated in the prior art. Twisted blades and multiblade structures would both involve additional noise creation, over a two-blade slightly twisted structure. However by suitable adjustment of the parameters we have defined characteristics which permit noise regulations to be kept, as now discussed with reference to Figures 5 to 9.

Figure 5 shows data gained by operating different blade designs at different speeds to give different air flows, ( x axis) and measuring the weight of grass collected from areas of equal growth before blockage of the duct 14 ( v axis). The data is given in full circles for central-disc, four blades (two speeds); in full triangles central disc, two blades (two ; and in full squares for feathered two-bladed blades. A good straight-line relationship is obtained.

Figure 6 shows that for a large range of blade designs the noise v. air-flow characteristics at constant speed (2400 rpm) relates generally to a straight line increasing at about 25 dB per decade (of arbitrary air-flow unit). The more a blade configuration falls to the right of this line the better is its noise/flow performance, and vice versa.

Figure 7 shows how, for two instances of standard blades (full circles) (F.R.=1.35) and square feathered blades (full diamonds) (F.R.=1.28), at a blade speed of 2400 r.p.m. the use of mere blades i.e. four blades instead of two, increases the noise level, other things being equal. This increase is about 10 or 15 dB per decade.

From Figures 6 and 7 alone, therefore, the use of higher-performance blades, and higher numbers of blades can both be expected to increase the cutter-deck noise.

Figure 8 however, shows that using for example a high-performance cutter blade, as shown in Figure 2, there is a very steep fall in noise generation, of about 55dB/decade of air flow units as the blade speed is decreased. It has also been found that1 with enough blades, the efficiency of grass-cutting is still adequate, and with a number of such high-performance blades the air-flow is still adequate.

Figure 9 therefore shows diagrammatically the combined novel and inventive effect of the parameters studied separately in Figures 5, 6, 7 and 8. The use of higher peformance blades is intrinsically noisier ("blade design" curve) Figure 6. The use of more blades is also noisier ("blade number" curve) Figure 7. The unexpectedly rapid decreasing speed in cutter deck noise with decreasing speed1 however, allows operation in the desirable less-than-80 dB zone (compare Figure 8)while still giving good grass cutting, because of the number of blades, and grass uptake, because of the blade design.

The invention also provides ancillary noise-reduction features concerned with the air exhaust from the cutter deck. In the same way as engine exhaust is a significant source of engine noise, and is typically treated as a distinct problem, the air-exhaust f-rom the cutter deck is a source of noise and is preferably also modified. To some extent, of course, the use of a grass collection box 12, cuts down cutterdeck exhaust noise. We have also found two other expedients, shown in Figures 10 and 11.

Figure 10 shows diagrammatically the underside of the dished cover of the cutter deck. The air offtake is conventionally guided by a rib 40 of diminishing height, at the underside of the cover1 progressively defining an air deflection to the outlet 41. The "cleaning-upli effect of the removal decreases the noise output, and also has the mechanical advantage of permitting a smaller cover or hood under which raised portions 27 of th blades 20 can freely rotate.

Figure 1 shows diagrammatically a modification to the joint between outlet 40 and "banana" shaped outlet duct 14. In this modification, the joint is a simple sliding overlap (the outlet 40 located within duct 14) as close to the cover 1G as possile, to give as clean a streamline effect as possible, The man skilied in the art will realise that the use of lower cutter speeds does not mean that less horsepower is required. Our concept is to provide an engine of sufficient maximum horsepower at full RPM, which when de-rated to 2800 rpm, still provides sufficient power to drive the cutting rotor and fan at the determined speed.

There is a tendendency for prior engines applied to known cutter decks are therefore either too noisy or too weak. However, the nominal 12 H/P. engine run at 2700-2850 r.p.m. with asuitable pulley ratio to run the 8-blade disc at say 1750 r.p.m. can satisfy the noise requirements especially if, as discussed below, ancillary noise-reduction of the engine, engine compartment and engine exhaust is incorporated.

A worked comparison upon a standard model ride-on mower, and modified noise-reduced version, gave the following results.

Standard Modified Engine Speed, r.p.m. 3500 2850 Cutter Speed, r.p.m. 2500 1750 Blade Tip Velocity ft.min. 19640 13750 Ex-t Air Velocity ft/min 7200 7500 Average noise at 4m. from cutter axis in dBA 89 79.5 The expedients to be adopted to reduce engine noise and related noise may include (a) side shielding, as shown in Figure 12, in which, to each side of the cutter deck extra panels 50 are fitted, by vertically extending bolts 51 at the top and spacer bolts 52 at the bottom to existing top panel 53 and chassis 54 respectively.

Resilient mountings are preferred.

(b) Sound-absorption foam panels, especially beneath the top and within the side shields or engine panels.

Typically, a medium density open cell foam with ideally a protective membrane coating is used, in a thickness up to 25 mm.

(c) Sound-damping layers to prevent "drumming" or resonance. Numerous spray-on or glue-on proprietary materials are known for this purpose. About 1 to 3 mm thickness is usual.

(d) Exhaust system modifications may be incorporated.

For example, benefit has been found by incorporating a standard "Super Lo-Tone" silencer plus arrestor and deflector instead of the standing "Nelson " muffler.

(e) Exhaust system orientation, i.e. to exhaust vertically is another practical noise reducing expedient.

Other conventional noise-reduction means either to the engine or to the cutter deck (e.g. a flexible peripheral skirt and intakes of air in the cover ) could also be incorporated.

Claims (11)

Claims.
1. A ride-on lawnmower in which an engine is provided to drive a circular cutter disc to rotate about a vertical axis, said disc carrying at least four blades in balance about the pivot and protruding from the periphery of the disc, each blade having an axially outer leading cutter edge and an axially outer trailing edge a portion of which is upwardly turned behind at least part of the cutting edge length to increase air flow and cutting performance to an extent sufficient to offset predetermined low speed engine and cutter operation governing noise production.
2. A ride-on lawnmower as claimed in claim 1 having eight such blades on the disc.
3. A ride-on lawnmower as claimd in claim 1 or 2 in which the blades protrude by more than half of their length from the disc.
4. A ride-on lawnmower as claimed in claim 3 in which the blades are sharpened with a leading edge for less than half of their overall length.
5. A ride-on lawnmower as claimed in any one preceding claim in which the upwardly turned trailing edge of each blade is shorter than the cutting edge thereof.
6. A ride-on lawnmower as claimed in claim 5 in which the upwardly turned trailing edge of each blade is from 30 to 70% of the length of the cutting edge thereof,
7. A ride-on lawnmower as claimed in one preceding claim in which the upwardly trailing edge of each blade is turned up to an extent of about half of the width of the blade and at an angle of 40 to 600 to the plane of the blade.
8. A ride-on lawnmower as claimed in any one preceding claim in which the overall diameter between blade tips is from 50 to 100 centimetres.
9. A ride-on lawnmower as claimed in any one preceding claim in which the pulley ratio between the engine and the circular cutter ts from 1.3:1 to 1.5:1, whereby the disc may be rotated at 1500 to 2000 r.p,m. by an engine operating at 2500 to 3000 r.p.m.
10. A ride-on lawnmower as claimed in any one preceding claim further comprising an internally smooth cutter deck hood to minimise generated noise.
11. A ride-on lawnmower as claimed in claim 1 substantially as herein described with reference to the accompanying drawings.
GB8803443A 1988-02-15 1988-02-15 Lawnmower Expired - Lifetime GB2215176B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8803443A GB2215176B (en) 1988-02-15 1988-02-15 Lawnmower

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB8803443A GB2215176B (en) 1988-02-15 1988-02-15 Lawnmower

Publications (3)

Publication Number Publication Date
GB8803443D0 GB8803443D0 (en) 1988-03-16
GB2215176A true GB2215176A (en) 1989-09-20
GB2215176B GB2215176B (en) 1992-09-16

Family

ID=10631716

Family Applications (1)

Application Number Title Priority Date Filing Date
GB8803443A Expired - Lifetime GB2215176B (en) 1988-02-15 1988-02-15 Lawnmower

Country Status (1)

Country Link
GB (1) GB2215176B (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003096786A1 (en) * 2002-05-21 2003-11-27 Pbl Sa Rotary lawn mower blade

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB950438A (en) * 1962-01-31 1964-02-26 Ransomes Sims & Jefferies Ltd Improvements in or relating to rotary mowing machines
US3918241A (en) * 1974-10-16 1975-11-11 Herbert C Stillions Cutting unit for rotary lawn mowers
GB1478780A (en) * 1975-01-02 1977-07-06 Victa Ltd Recessed cutter disc for rotary lawnmower
GB1516875A (en) * 1974-08-02 1978-07-05 Toro Co Low speed rotary mower
US4214426A (en) * 1977-01-18 1980-07-29 Stiga Ab Noise damping arrangement in rotating cutting devices
US4559769A (en) * 1982-07-26 1985-12-24 Outboard Marine Corporation Cutter blade for pneumatically transporting grass clippings

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB950438A (en) * 1962-01-31 1964-02-26 Ransomes Sims & Jefferies Ltd Improvements in or relating to rotary mowing machines
GB1516875A (en) * 1974-08-02 1978-07-05 Toro Co Low speed rotary mower
US3918241A (en) * 1974-10-16 1975-11-11 Herbert C Stillions Cutting unit for rotary lawn mowers
GB1478780A (en) * 1975-01-02 1977-07-06 Victa Ltd Recessed cutter disc for rotary lawnmower
US4214426A (en) * 1977-01-18 1980-07-29 Stiga Ab Noise damping arrangement in rotating cutting devices
US4559769A (en) * 1982-07-26 1985-12-24 Outboard Marine Corporation Cutter blade for pneumatically transporting grass clippings

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003096786A1 (en) * 2002-05-21 2003-11-27 Pbl Sa Rotary lawn mower blade

Also Published As

Publication number Publication date
GB2215176B (en) 1992-09-16
GB8803443D0 (en) 1988-03-16

Similar Documents

Publication Publication Date Title
US5794306A (en) Yard care machine vacuum head
US5381970A (en) Combination chipper/shredder and vacuum apparatus for lawns and gardens
AU661661B2 (en) Multi-bladed mulching mower
CA2080993C (en) Lawn and garden chipper shredder vacuum apparatus
US5094065A (en) Mulching rotary lawn mower blade
US8746186B2 (en) Rotating screen for centrifugal fan
US6928693B1 (en) Blower with dual tubes
US3688479A (en) Leaf comminuting apparatus
US5435118A (en) Vacuum sweeper shredder rotary mower
US7093415B2 (en) Lawn mower having adjustable flow control baffle
CA1099114A (en) Mulching lawn mower
US3783592A (en) Garden grooming machine and rotor therefor
CA1071546A (en) Air supply apparatus
CA2405207C (en) Lawn mower
EP0664945B1 (en) Convertible lawn mower
US5305589A (en) Mulching deck
US3568421A (en) Lawn mower
US6427429B1 (en) Multiple string lawnmower
US4589249A (en) Mowing apparatus
US4158279A (en) Riding mower with grass collecting system
US5129217A (en) Multiblade mulching mower
US4614080A (en) Grass collector blower
US6430906B1 (en) Mower deck attached trimmer
US6892461B2 (en) Weed trimmer safety guard
US9491905B2 (en) Cross flow horizontal rotary lawn mower with airfoil blades

Legal Events

Date Code Title Description
PE20 Patent expired after termination of 20 years

Effective date: 20080214