Classifications

• • A—HUMAN NECESSITIES
  • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
  • A01D—HARVESTING; MOWING
  • A01D34/00—Mowers; Mowing apparatus of harvesters
  • A01D34/835—Mowers; Mowing apparatus of harvesters specially adapted for particular purposes
  • A01D34/90—Mowers; Mowing apparatus of harvesters specially adapted for particular purposes for carrying by the operator
  • A01D34/905—Vibration dampening means
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
  • F16C1/00—Flexible shafts; Mechanical means for transmitting movement in a flexible sheathing
  • F16C1/02—Flexible shafts; Mechanical means for transmitting movement in a flexible sheathing for conveying rotary movements

Definitions

• the invention relates in general to portable tools for gardening, which are provided with a rotating tool and a motor for powering the tool.
• the present invention relates to bush trimmers which are commonly used for cutting shrubs, bushes and the like.
• a bush trimmer generally comprises a rotating cutting tool, typically a disc provided with rigid blades or flexible nylon wires, which is protected by a surrounding safety casing and borne at an end of a rigid support rod provided with a grip.
• the support rod is internally hollow and houses a transmission system for connecting the rotating cutting tool to an activating motor, typically a small internal combustion motor, which is generally fixed to the opposite end of the support rod.
• an activating motor typically a small internal combustion motor
• a typical transmission system comprises a single rigid transmission shaft, which is rotatably housed in a coaxially position internally of the support rod, and is connected both to the cutting tool and to the activating motor.
• a drawback of this transmission system however consists in the fact that during passage through medium-to-low rotation speeds, the transmission shaft is subjected to torsional resonance phenomena, generated by the irregularities of functioning of the activating motor, which resonance is not only transmitted to the user in the form of unpleasant vibrations, but is also responsible for rapid wear of the transmission shaft, which can be subject to early breakage.
• a further known transmission system comprises a single flexible transmission shaft, which is generally used as it is more economical than the rigid shaft.
• This transmission system is not, however, free of torsional resonance, which is manifested at different frequencies than with the rigid shaft, due to the different torsion coefficient.
• the flexible-shaft transmissions exhibit further drawbacks, among which, for example, the drawback of transmitting only low-entity powers, lack of sufficiently strong resistance to impacts and, in general, to turn in a lower performance than transmissions with a rigid shaft.
• the aim of the present invention is to obviate the above-mentioned drawbacks, connected to torsional resonance phenomena, with a solution that is simple, rational and relatively inexpensive. These aims are attained by the characteristics of the invention as reported in the independent claim 1.
• the dependent claims delineate preferred and/or particularly advantageous aspects of the invention.
• the invention makes available a portable gardening tool comprising a rotating tool and a transmission system which connect the rotating tool to an activating motor, where the transmission system comprises a rotating shaft formed by at least two tracts having different torsion coefficients.
• torsion coefficient reference is made to the ratio between the applied torque momentum and the relative rotation of two sections of the shaft located at a unitary distance.
• the most elastic tract i.e. the tract with the lowest elastic torsion coefficient, is able to absorb the torsional vibrations transmitted by the most rigid tract during the transitory speeds, thus eliminating excessive vibrations and reducing the wear to which the whole transmission system is subjected.
• the most elastic tracts are preferably interposed between the most rigid tracts and the rotating tool.
• the most elastic tract is realised by a flexible shaft, which is located coaxially and is connected in series to a more rigid shaft.
• the flexible shaft is preferably constituted by steel wires which form a series of helical spirals wound one upon another, alternatively in opposite directions, welded at ends thereof to connection sleeves, and possibly closed inside a flexible sheath which serves to keep the spirals in well-lubricated condition.
• Flexible shafts of this type are, for example, Bowden cables.
• the transmission shaft formed by the most elastic tract and the most rigid tract is all inserted in the hollow and rigid support rod, with a rotating tool being fixed to an end thereof.
• Figure 3 shows the flexible shaft used in the transmission system of figure 2.
• Figure 4 is the shaft of figure 3, seen from IV.
• Figure 5 is the constructional structure of the flexible shaft 3.
• the bush trimmer 1 comprises a cutting tool 2, which is typically constituted by a rotating disc provided with rigid blades or belts or flexible nylon wires.
• the cutting tool 2 is protected by a surrounding safety casing 3, and is borne at an end of a rigid support rod 4, which is provided with at least a grip 5 which can be gripped by the user during use.
• the bush trimmer 1 further comprises an activating motor 6, in the example a small internal combustion engine, which is fixed to an end of the support rod
• the activating motor 6 is connected to the cutting tool 2 via the transmission system denoted globally by 7 and illustrated in figure 2.
• the transmission system 7 schematically comprises a rigid rotating shaft 70 and a flexible rotating shaft 71 , which are reciprocally coaxial and are connected in series by means of a connecting joint 72.
• the rigid shaft 70 and the flexible shaft 71 are both inserted coaxially internally of the hollow support rod 4 of the bush trimmer 1.
• the rigid rotating shaft 70 exhibits a fluted end 73, which projects externally of the support rod 4 for mechanically coupling with the activating motor 6, and an opposite threaded end 74, which is screwed into a first axial hole of the connecting joint 72.
• the rigid shaft 70 is rotatably coupled and supported internally of the support rod 4 by one or more guide bushings 75, and is axially blocked by means of known type and not illustrated in the figures.
• the flexible rotating shaft 71 is substantially conformed as a Bowden cable.
• the flexible shaft 71 comprises a central core 76 made of metal or plastic on which steel wires 77-80 are wound, which wires
• 77-80 form a series of helical spirals wound one on another, alternatively in opposite directions.
• the steel wires 77-80 can be en masse closed within a flexible sheath which serves to maintain the spirals in well-lubricated conditions.
• the ends of the helical spirals are welded to two connecting sleeves 81 and 82, which both have a polygonal transversal section which in the illustrated example is square.
• the flexible shaft 71 has a torsion coefficient K which is decidedly lower than that of the rigid shaft 70, which is formed by a single steel bar with a preferably solid transversal section.
• the flexible shaft 71 must have an overall length Q which is preferably above 50 mm, for example about 100 mm.
• the connecting sleeve 81 is coupled to the connecting joint 72, while the connecting sleeve 82 projects externally of the support rod 4 where it is coupled to a conical cogged pinion 83, which is rotatable and axially blocked with respect to the support rod 4.
• the connecting sleeve 81 is inserted in a second axial hole of the connecting joint 72, which exhibits a corresponding polygonal transversal section, such as to realise a sliding coupling which blocks them reciprocally in a rotational direction.
• the connecting sleeve 82 is inserted coaxially in a central through- hole of the cogged pinion 83, which exhibits a corresponding polygonal transversal section, such as to realise a sliding coupling which blocks them reciprocally in a rotational direction.
• the connecting sleeve 82 is further axially blocked by a block 84 of larger diameter, which is fixed to an end of the sleeve 82 and is received in an annular recess of the central hole of the cogged pinion 83.
• the flexible shaft 71 is substantially stretched between the connecting joint 72 and the pinion 83, such as always to be coaxial to the rigid shaft 70.
• the conical cogged pinion 83 enmeshes with a conical cogged crown 85, which is keyed on a tool-bearing chuck 86 having a rotation axis which is inclined with respect to the flexible shaft 71 and the rigid shaft 70.
• the cogged pinion 83 and the tool-bearing chuck 86 are received internally of a single hollow rigid body 87, which comprises two cylindrical portions 88 and 89, reciprocally communicating, which are destined respectively to receive the cogged pinion 83 and the tool-bearing chuck 86.
• the cylindrical portion 88 is inserted and fixed to an end of the support rod 4.
• the cogged pinion 83 is rotatably coupled to the cylindrical portion 88 by means of interposing a pair of radial ball bearings 90, which are axially blocked between the conical head of the cogged pinion 83 and the front edge of the support rod 4.
• the tool-bearing chuck 86 is in turn rotatably coupled to the cylindrical portion 89 by interposing a pair of radial ball-bearings 91 , which are axially blocked by a ferrule 92 which closes the open end of the cylindrical portion 89.
• the tool-bearing chuck 96 exhibits a tract which projects from the closing sleeve 92 towards an outside of the cylindrical portion 89, on which the cutting tool 2 is keyed.
• the motor 6 sets the rigid shaft 70 and the flexible shaft 71 in rotation about the axis thereof, such that the enmeshing between the cogged pinion 83 and the cogged crown 85 causes the tool-bearing chuck 86 to rotate, which chuck 86 in turn draws the cutting tool 2 in rotation.
• the torsional vibrations transmitted by the motor 6 are in part absorbed by the flexible shaft 71 , the coils of which tend to twist, squeezing against one another and thus demonstrating a certain torsional elasticity. In this way, it is possible to limit the vibrations which are produced and transmitted during the passages through average-to-low rotation speeds, consequently reducing the stresses and therefore the wear to which the transmission system 7 is subjected.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Environmental Sciences (AREA)
• Health & Medical Sciences (AREA)
• Oral & Maxillofacial Surgery (AREA)
• Mechanical Engineering (AREA)
• Harvester Elements (AREA)

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• 2008
  • 2008-11-13 WO PCT/IT2008/000709 patent/WO2010055532A1/en active Application Filing
  • 2008-11-13 EP EP08876098A patent/EP2346315A1/de not_active Withdrawn

Non-Patent Citations (1)

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