TECHNICAL FIELD

The invention relates to devices for pruning, in particular to shears, used for cutting branches or vine-shoots.

BACKGROUND ART

Manually operated shears are known, as well as the ones operated electrically or pneumatically or hydraulically, which use suitable operating means connected with the shears handgrip.

Electric, pneumatic or hydraulic energy necessary for operating these shears is supplied by external sources,- the engine of electric shears is fed with energy supplied by an accumulator carried by the operator on his shoulder, whereas pneumatic or hydraulic shears can be used only if a source of compressed air or a hydraulic pump, respectively, is present near the place, in which the device is used.

The disadvantage of the electric shears results from the high cost and the weight of the assembly shears-accumulator, while the pneumatic and hydraulic solutions are not practical, because of the pipes of compressed air or liquid and the use of noisy motor-compressor or pumping group.

DISCLOSURE OF THE INVENTION

An object of the present invention is to propose shears that are easy to handle, that can be operated without external energy sources, and have high autonomy and reduced weight. A further object of the subject invention is to propose mechanically simple, reliable and cheap shears.

The above mentioned objects are obtained in accordance with the contents of claims, by means of a driver assembly equipped shears for cutting bran¬ ches or the like, the said shears including a hand¬ grip and a pair of shearing blades, namely a sta¬ tionary blade and movable blade, pivoted to each other and to an external end of the said handgrip. The driver assembly (30) include.- a cylinder, contained in the handgrip and featuring conduits, respectively a suction conduit and exhaust conduit, leading to openings made in the wall of the cylinder,- a piston sliding inside the cylinder and linked to the movable shearing blade via a piston rod; a cylinder head fixed to the cylinder and featuring a combustion chamber,- elastic means associated to the said piston so as to push it towards the said combustion chamber thus opening the movable blade with respect to the sta¬ tionary blade,- feeding means supported by the cylinder head aimed at withdrawing a pre-set quantity of fuel from a reservoir and injecting this fuel under pressure into the combustion chamber,- ignition means also supported by the cylinder head for firing an exploding mixture formed in the said combustion chamber by the said fuel and air, thus starting the active stroke of the piston and pro-

gressively moving the movable blade towards the stationary blade.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristic features of the present invention are pointed out in the following descrip¬ tion with reference to the enclosed drawings, in which:

- figure 1 shows a lateral view of the shears,-

- figures 2a and 2b show sectional lateral views of the shears with the blades open and close, respect¬ ively; - figure 3 shows a partial lateral view of the shears as seen from the side opposite to the fig. 1 view;

- figure 4 shows a section taken along line IV-IV of fig. 1; - figure 5 shows a section taken along line V-V of fig. l;

BEST MODE OF CARRYING OUT THE INVENTION

With reference to the above described fig¬ ures, the shears 100 substantially include an anato¬ mical handgrip 1 and a pair of blades 2, 2a, namely a stationary blade and movable blade, pivoted to each other in correspondence of the outer end la of the handgrip 1.

The shears 100 are equipped with a driver assembly 30, described in the following in a more detailed way, whose operation can be compared with a internal combustion two-stroke engine with con-

trolled ignition, aimed at working continuously between a minimum and maximum revolution rate, but different from it because operating in single im¬ pulses fashion. An active stroke and a return stroke of a piston 32 correspond to each of the single impulses. The driver assembly 30 is connected to the movable blade 2a and keeps this latter open, with respect to the stationary blade 2, during the return stroke of the piston 32.

During the active stroke of the piston 32, the movable blade 2a is instead closed, with respect to the stationary blade 2.

The driver assembly 30 includes a cylinder 31, contained in the handgrip 1, with the piston 32 sliding inside the said cylinder and linked to the movable shearing blade 2a by means of a piston rod

33.

The cylinder 31 features a suction conduit 31a and an exhaust conduit 31b, leading to openings 310, 320 made in the wall of the cylinder.

The opening 310 communicates with a blow off spout 311, equipped with a protection net 312 that prevents foreign matters from entering the conduit 31a (figs. 1 and 5) .

The openings 320 communicate with a silencer 321 (figs. 1 and 4) .

A cylinder head 35 is fixed to the cylinder

31 in correspondence with the internal head lb of the handgrip 1 and features a combustion chamber 36.

Elastic means 40 are placed between the part of the piston 32 to which the piston rod 33 is articulated and a ring-like stop 313, made in the cylinder 31 on the opposite part with respect to the head 35 (fig. 2a) .

The elastic means 40 push the piston 32 toward the combustion chamber 36.

The driver assembly 30 includes also feeding means 60, supported .by the cylinder head 35, and including as follows: a reservoir 61 filled with fuel and compressed air, connected, via a first duct 62, to a proportioning valve 63, that is in turn connected, via a second duct 64 to an injecting nozzle 65 directed inwards of the combustion chamber 36.

The same cylinder head 35 supports also ignition means 70 for firing and exploding mixture formed in the combustion chamber 36, and including a piezoelectric transducer 71 aimed at supplying high voltage impulses to an ignition spark 72 situated inside the combustion chamber 36.

The driver assembly 30 includes also activa¬ ting means 50 comprising, in the illustrated exam¬ ple, a manually operated lever 51 having prongs 51a, si (fig. 2) for respectively controlling in se¬ quence the proportioning valve 63 and the piezoelec¬ tric transducer 71.

The reservoir 61 is filled by removal of the bottom 610, introduction of a pre-set quantity of fuel, anyway less than the volume of the reservoir 61 thus leaving an empty space, putting on again the bottom 610 and introduction of compressed air into the reservoir via a valve 613 integral with the bottom, until the required pressure is obtained. The fuel pushed by the compressed air is kept by the proportioning valve 63 close in its idle position.

In figure 2a the shears 100 are in the idle position, in which the piston 32 is near the combus- tion chamber 36 and the blades 2, 2a are open.

When the shears 100 are in the idle position and the piston 32 is near the combustion chamber 36, the air, contained in the latter and sucked in the previous cycle, is compressed as a result of the return stroke of the piston 32 caused by the elastic means 40.

Operating of the lever 51 causes in sequence: opening of the proportioning valve 63 (prong 51a) , delivery of a pre-set quantity of fuel under pres- sure to the nozzle 65 for the injection of this pre¬ set quantity of fuel in the combustion chamber, operating the piezoelectric transducer 71 (prong 51b) that generates the spark in the ignition plug 72. Consequently, this provokes explosion of the mixture air/fuel and the subsequent active stroke of a piston 32 that closes the movable blade 2a with respect to the stationary blade 2, against elastic reaction of the elastic means 40 (fig. 2b) . During its active stroke, the piston 32 uncovers first the exhaust conduit 31b, allowing burnt gases to evacuate, then the suction conduit 31a that, exploiting also depression formed in the cylinder after the rapid evacuation of burnt gases, allows fresh air to be introduced to the cylinder.

When the explosion force is terminated, the elastic means 40 cause the return stroke of the piston 32, thus compressing air introduced to the cylinder via the suction conduit on one side, and opening the shearing blades again on the other side.

If the shears are not used for a long time, the pressure of air in the combustion chamber 36 could be lowered because of inevitable leaking between the elastic rings of the piston 32 and the cylinder 31.

In this case it is enough to act manually on the movable blade 2a so as to make the piston 32 perform the complete cycle (active and return strokes) . The pressure of air in the reservoir is big enough to inject the fuel even if the latter is getting exhausted.

The proportioning valve 63 is adjustable, so that it can suitably dose the quantity of the fuel sent to the injection nozzle 65.

In the illustrated solution, the head 35 is connected to the cylinder 31 by a threaded joining made between the head and the end lb of the handgrip

1, that acts as a seal, since made of plastic mater- ial.

The threaded joining allows to remove in simple way the head 35 from the handgrip l, thus facilitating maintainance operations.

The material, of which the handgrip is made, isolates thermally the cylinder from the user hand. It is important to point out that even in¬ tense use of the shears does not cause such increase of its temperature big enough to prevent its using, since the frequency of explosions, if compared with the minimum operation rate of an ic engine, is anyway extremely limited.

Moreover, it is easy to understand that a reservoir, apparently small, can guarantee a big operation autonomy, due to really reduced consump¬ tion.

Anyway, also refilling of the reservoir is simple and rapid.

INDUSTRIAL APPLICABILITY

All what has • been said above results in practicity of the shears, being the subject of the present invention, independent from any kind of external source of energy and, at the same time, extremely light and compact.

It is also to be pointed out that cutting power of the shears is very big, because of rapid power supply.

The proposed technical solution is mechanic¬ ally simple, reliable and cheap.

The type of fuel use in the exemple herein described is the one used for explosion engines, e.g. petrol (possibly mixed with oil), methane, L.P.G. (liquid petroleum gas), ethanol .

Therefore all possible detail variants neces¬ sary for improvement the shears functioning are protected by the present technical solution, as described above and claimed in the following.