WO2014045264A1

WO2014045264A1 - Breaker for excavators with optimized hydraulic circuit

Info

Publication number: WO2014045264A1
Application number: PCT/IB2013/058811
Authority: WO
Inventors: Oscar CARRISI; Giammichele CALO'; Giacomo CATANZARO
Original assignee: Tecna Group Srl
Priority date: 2012-09-24
Filing date: 2013-09-24
Publication date: 2014-03-27
Also published as: EP2897769B1; EP2897769A1; ITBA20120055A1; ES2904312T3

Abstract

Breaker (1) for excavator comprising a body (10) inside which a hydraulic circuit is formed which can be supplied from the outside with liquid under pressure, said hydraulic circuit comprising: an inlet (13) for the liquid under pressure; an outlet (18) for the return of the liquid under pressure to the supplying circuit; an active thrust chamber (ll)with a first diameter and a passive thrust chamber (20); ducts (12, 21) to connect said active thrust chamber (11) and said passive thrust chamber (20) to said inlet (13); a piston (15) configured so that it can slide in areciprocating motion inside said breaker under the thrust of said liquid under pressure wherein said piston (15) is provided, at the active thrust chamber (11), with a projection with a second diameter (C) smaller than the first diameter of the active thrust chamber (11), said projection being wholly contained inside the active thrust chamber (11).

Description

The present invention relates to a breaker for excavators with optimized hydraulic circuit

At the state of the art there are known various embodiments of breakers for excavators.

The principle according to which the known breakers work can be described with reference to figure 1. In these excavators hydraulic liquid under pressure goes in an active thrust chamber (11) through ducts (12) connected to an input socket (13) of the liquid under pressure. To these ducts (12) there is connected a first volume (142) of an accumulator (14). An elastic membrane (143) divides said volume full of liquid under pressure (142) from a second volume containing nitrogen (141). Therefore, the elastic membrane (143) allows the volume (141) to be exploited as an accumulation volume. The principal function of the accumulator (14) is to accumulate oil in the passive step (when the piston goes from PMI to PMS) in order to return it in active step when the flow rate needed in the thrust chamber (11) is greater than the one provided at the inlet (13) of the breaker.

During the active thrust step, the pressure exerted by the oil contained in the active thrust chamber

(11) acts on the upper surface (151) of a piston (15) which transmits the force exerted by the oil to the tool (16) which is used to break.

A distributor (17) is concentric with respect to the piston (15). The distributor is needed to put the active thrust chamber (11) alternately in communication with both the portion under low pressure of the circuit (18) connected to the return under low pressure of the oil, and with the inlet under high pressure (13) .

When the piston (15) is in the thrust step, the thrust chamber (11) is separated from the portion under low pressure (18) of the hydraulic circuit of the distributor (17).

It is also provided a passive thrust chamber (20) connected to the oil supply under pressure through a series of ducts (21) . Only for illustration, in figure 1 it is shown only one duct which connects the passive thrust chamber to the supplying circuit, but it is also possible to use different configurations, for example three ducts arranged at 120°.

On the lower surface (152) of the piston (15) which faces the passive thrust chamber (20) the oil under pressure acts on a circular crown, whose area is clearly smaller than the area (151) on which the oil acts in the active thrust chamber (11) . Therefore there is created an unbalance between the two forces acting on the piston in vertical direction, and this unbalance thrusts the piston downwards. The downwards stroke of the piston (15) is the active part of the cycle. In this step, the piston, by striking on the tool, transmits it its kinetic energy and so exerts a force on the tool of the breaker, which then breaks the material being worked .

When the piston (15) reaches the lower dead point, the system is such that, in that position, the piston (15) leaves free the lower portion of the distributor (17).. Since the lower portion of the distributor (17) is greater than the upper one, the resultant of the forces acting on the distributor is such that it is moved upwards. In its vertical movement the distributor (17) closes first the high pressure gap and than leaves free the discharge gap of the active thrust chamber (11), thus disconnecting the active thrust chamber (11) from the high pressure circuit and connecting it to the low pressure one. In this way, the new resultant of the forces acting on the piston (15) is such that it is thrust upwards and it is put again in the starting position, reestablishing the cycle as well. The bypass (19) serves when the distributor, while going down, closes the discharge gap. In this moment, the oil which is between the distributor (17) and the piston (15) (in this step, the distributor is inserted around the piston) has to be discharged because the distributor (17) is going down, and the discharge occurs through the bypass (19). As yet said, the piston (15) acts on a tool (16) used to break the material being worked. The tool (16) is provided with a groove (163) whose ends (161, 162) define the maximum axial amplitude possible allowed by the tool. In the groove (163) of the tool (16) is in fact engaged a tool-stopper (25) integral with the breaker (1), which limits the axial amplitude allowed by the tool (16).

The described functioning is typical of breakers for hydraulic hammers known at the state of the art .

The breakers for excavators known at the state of the art have many drawbacks, among which the fact that the described functioning is independent of the fact that the bit of the tool (16) is actually working material or not. This is a problem since the force as a whole exerted by the pressure of the liquid provided in the active thrust chamber (11) on the piston (15) and so on the tool (16), which should serve to break the material being worked, when the bit idles is discharged on the tool- stopper (25) , thus subjecting it to high stresses which can lead shortly to deformation of the same and so to expensive machine-stop times.

Another drawback of the breakers known at the state of the art is linked to the sudden pressure variations, which are provided in the hydraulic circuit during the cycle, caused by a not optimized conformation of the hydraulic circuit. In fact, in order to reduce the absorbed couple of the pumps, the last generation excavators use oil pumps with variable piston displacement with maximum flow rates with respect to the one used in the old excavators. This implies that, while the flow rate at the breaker inlet is reduced proportionally to the traditional one used in the breakers, at the accumulators there are requested greater expansions, which cause greater pressure variations and so an efficiency reduction. In particular, during the active . step of the cycle, when the thrust chamber is put under pressure by the oil of the circuit under high pressure, pushing the piston downwards to strike the tool, it is needed to guarantee that the chamber is under pressure for the whole active step notwithstanding the expansion due to the piston going down. In order to do so, it is needed that the hydraulic circuit of the breaker is such that it guarantees, once the conditions of flow rate and supplying pressure determined by the excavator on which the breaker is mounted are fixed, the passage of the flow rate needed to fill the volume of the thrust chamber constantly. As a way of example, and without this limiting the aims of the invention, it is needed to guarantee a good functioning with oil flow rates supplied by the excavator reduced by 20% with respect to an excavator of equal weight known at the state of the art. Approximately, a hammer of 200 kg according to the present invention uses flow rates between 40-45 1/min .

Another drawback of the breakers for excavators known at the state of the art is linked to the need to increase the mass of the piston in case of equal dimension of the same and piston displacement of the breaker, in order to increase the force transmitted to the tool.

In fact the theoretical maximum potential striking energy is constant and can be obtained by the following expression:

Pressure x thrust area x piston stroke = 0,5 x mass x speed² Therefore by doubling the mass, the speed is reduced by a ratio equal to l/radQ(2), about equal to 1,414<2. It is deduced that the momentum, resulting from the product of the piston mass for its speed increases while the piston mass increases as well, and since the force transmitted to the tool is equal to the momentum variation in time, since the striking time is about constant at the mass variation and the starting momentum is equal to zero (stationary tool) it is deduced that, at equal piston displacement and supplying pressure the force transmitted increases while the tool mass increases as well.

So it is clear that a technical problem linked to the optimization of the pistons is to increase the mass of the piston while maintaining constant the supplying pressure, the piston displacement and the whole dimension of the breaker.

Therefore, aim of the present invention is to provide a piston with optimized geometry to increase the mass of the same piston in case of equal breaker dimension. According to another aim the present invention provides a breaker for excavators which solves the problems of the state of the art, and in particular which is provided with a system which allows to disconnect automatically the tool from the high pressure circuit when not actually working on the material to be destroyed. Moreover, the breaker object of the present invention aims at providing a hydraulic circuit optimized to guarantee a correct functioning of the breaker with low oil flow rates. The invention, object of the present invention, realizes the prefixed aims since it is a hydraulic breaker for excavator comprising a configuration such that it can slide alternatively, inside said breaker under the thrust of a hydraulic liquid contained in a circuit comprising at least a first thrust chamber, said active, and a second thrust chamber, said passive, characterized in that the piston is provided, at the active thrust chamber, with a projection with diameter (C) smaller than the diameter (A) of the thrust chamber, said projection being contained in the active thrust chamber as a whole, and having, preferably, an axial extension equal to at least half diameter of said thrust chamber.

In addition the invention provides a breaker for excavator with a by-pass system to avoid idle working. Said bypass system comprises a bypass between the high pressure portion and the low pressure portion of the hydraulic circuit, configured such that, in the normal working conditions (so with a resistance provided by the tool by the material being worked) the bypass is closed by the piston. Without resistance provided by the material being worked to the tool, the tool (and so the piston) is subject to a greater axial amplitude. In this case the bypass is freed and the high pressure circuit is put in communication through the bypass gap with the low pressure circuit. In this way, inside the breaker there is only low pressure, the piston is blocked in its position at P I and cannot go up again any more. The breaker stops functioning. When the operator positions the breaker against the material to be worked again, the bypass is closed and the normal functioning, previously described, is reestablished .

These and other advantages will be clear from the following description of the invention with reference to the appended figures 1 to 9.

Figure 1 shows an embodiment of a breaker known at the state of the art, and whose functioning was described at the beginning.

Figure 2 shows a preferred embodiment of the breaker according to the present invention. Figure 3 shows a detail of the embodiment of the discharge gaps according to another preferred embodiment of the breaker according to the present invention;

Figure 4 shows a detail of an embodiment of the discharge gaps according to the known state of the art .

Figure 5 shows a detail of the discharge bypass comprised in the breaker according to the present invention;

Figure 6 shows a detail of the oil supplying system of a preferred embodiment of the breaker according to the present invention.

Figure 7 shows a graph with the flow of the pressure in the thrust chamber and of the discharge pressure during the typical cycle of a breaker known at the state of the art

Figure 8 shows a preferred embodiment of the piston according to the present invention.

Figure 9 shows the piston shown in figure 8 mounted inside a breaker according to the present invention.

Figure 10 and figure 11 show two embodiments of breakers for excavators known at the state of the art, described in EP1964647 and US4281587. As it is shown in figure 8, the piston (15) according to the present invention is symmetrically shaped around an axis (150) and is provided with three diameter discontinuities which define four different diameter sections (A, B, C, D) .

In particular, the discontinuity between the greater diameter section (B) and the smaller diameter section (D), when the piston (15) is mounted in the breaker (1) as it is shown in figures 2, 9, 5 faces the passive thrust chamber (20) . The circular crown deriving from the discontinuity defines the surface on which the pressure of the liquid present in the thrust chamber (20) acts in axial direction.

The section with diameter (A) , which in the piston according to the present invention is smaller than the diameter (B) , is in the active thrust chamber and defines the thrust surface in axial direction of the liquid under pressure. The presence of another diameter section (C) , said diameter (C) being smaller than the diameter of the active thrust surface (A) allows to occupy at least partially the volume of the active thrust chamber, increasing the mass of the piston in case of equal dimensions of the breaker (1) and piston displacement . In order to understand the technical effect obtained by means of this configuration of the piston, it is to be considered that in the embodiments known at the state of the art, shown for example in figures 10 and 11, the piston is provided with a projection at the active thrust chamber. The projection, which is actually a piston section with smaller diameter of the active thrust chamber diameter, is extended beyond the upper limit of the active thrust chamber. The liquid under pressure acts on a surface having circular crown shape defined outside by the diameter of the active thrust chamber and inside by the diameter of the projection.

In the piston according to the present invention instead, at the active thrust chamber the piston is provided with a projection with diameter (C) smaller than the diameter (A) of the thrust chamber. Said projection, contrary to what happens in the embodiments of the state of the art, is contained as a whole in the active thrust chamber.

In this way, the liquid under pressure can act on a circular surface defined by the diameter (A) of the thrust chamber (increasing the force exerted at equal pressure) , but the reduction in piston mass is limited at the minimum. According to a not limiting preferred embodiment, the axial extension of the projection is equal to at least the half of the diameter of the thrust chamber.

Therefore, this measure increases the force exerted by the piston (15) on the tool (16) . Moreover, the presence of the projection with diameter (C) , by reducing the volume of the active thrust chamber (11) when the piston is around its upper dead point and the gap under high pressure is freed, allows a more rapid pressurization of the active thrust chamber ( 11 ) .

As it is shown in figure 2, the breaker for excavator according to the present invention comprises a piston (15), which acts on the tool (16) according to what described at the beginning. The high pressure supplying circuit of the breaker comprises an inlet (13) connected with the active thrust chamber (11), and through the duct (21), with the passive thrust chamber (20) . The supplying circuit is also provided with an annular groove (22) communicating with the high pressure circuit. As yet described, the shape of the piston (15) according to the present invention is such that the side surface of the piston is provided with some diameter discontinuities and in particular the piston in the upper portion has a diameter (A) W smaller than the cylinder in which it slides, so that it is created a recess between the piston (15), the cylinder and the reduction bushing (24) arranged between the piston and the cylinder, where it is obtained the duct (23) .

In the lower portion with respect to the portion with diameter (A) , the diameter (B) of the piston (15) is such that the piston (15) slides in the seat obtained in the body of the breaker (1) , and at the same time that the sealing with respect to the. bypass is obtained, comprising the annular groove (22) or a series of holes provided in radial direction on the inner surface of the sliding seat of the piston. In practice, when at the annular groove (22) there is the portion with greater diameter (B) of the piston (15), the groove is not communicating with other ducts other than the supplying duct (21) .

According to another embodiment not shown in figure, the annular groove (22) can be substituted by one or more holes provided in radial direction, or by ducts of other shape, as long as they are useful to the aim.

If the piston has a greater amplitude than the working one, the portion of the piston with smaller diameter (A) is at the annular groove (22) . In this way, the annular groove (22) communicates, through the duct (23) , with the return under low pressure of the oil (18) .

Therefore, a preferred path is created for the oil under pressure made up of the supplying section

(21) , the annular groove (22) and the return duct (23) . The possibility for the oil to follow this preferred path depends on the axial position of the piston, and so, of the tool. As yet said, this implies that in the hammer there is only low pressure, because the high pressure inlet (13) is short-circuited with the outlet under low pressure (18) .

When the tool meets resistance, it tends to thrust the piston upwards, thus maintaining the axial functioning amplitude in the range. When the thrust exerted by the material being worked is removed, the piston tends to thrust downwards the tool beyond the allowed ^' limit . In this way, however, it is freed the annular groove (22), which, by realizing the described by-pass, annuls the pressure forces acting on the piston, which is blocked at the lower dead point, leaving the groove

(22) in communication with the groove (154) and so with the duct (23) . Thus, it is realized a breaker for excavator according to the prefixed aims.

According to other preferred embodiments, the just described breaker can be modified as better described in the following.

In particular, the variations with respect to the known state of the art, aim at reducing the piston displacement in case of equal force exerted, at optimizing the ratio between the accumulator volume and the piston displacement, in addition to the layout of the high and low pressure circuits in order to reduce the charge loss and at the same to avoid pressure peaks.

The piston displacement of a breaker is given by the upper surface of the piston, i.e. the surface of the active thrust chamber, for its stroke.

During the active step, when the thrust chamber is put under pressure by the oil of high circuit, thrusting the piston downwards to strike the tool, it is needed to guarantee that the chamber is pressurized for the whole active step notwithstanding the expansion due to the piston going down. Having an insufficient oil flow rate implies a worst pressurization and a reduction of the striking speed of the piston on the tool. To avoid this phenomenon, in the breaker for excavators according to the present invention the piston displacement is reduced, reducing the diameter (A) of the thrust chamber. For example, without this being limiting for the aims of the present invention, for hammers between 200 and 300 kg it is presumable ^the use of thrust chambers with diameter between 40 and 45mm. The reduction of the piston displacement implies that during the active step the hammer needs less oil, so it can also function with lower flow rates. But in order to maintain a correct functioning of the system it is needed that the geometry of the piston (15) is modified. In particular, the piston (15) is provided with a diameter of active thrust smaller than the one of passive thrust (A<B) . It is particularly useful to act on the diameter instead on the stroke to reduce the piston displacement, because, since the piston displacement is proportional to the diameter squared, to intervene on the diameter has a greater action than to intervene on the stroke. Reducing the diameter of the active thrust chamber, and maintaining however unaltered the mass of the piston (15), since this one determines the kinetic energy for the breaking, it is needed to increase the diameter of the piston

(15) in the lower portion, in order not to have to increase its length. Further, the just described provision of the projection with diameter (C) allows the mass to be further increased at equal dimension of the piston (15) .

The increase in length can be in fact disadvantageous for dimension reasons and also because too thin pistons are not apt to transmit the striking energy to the tool, which has dimensions more or less fixed for commercial reasons. Generally, it is convenient that the piston has a diameter about the same as the tool, but never lower, in order to maximize the striking energy transmission. Therefore, the variations of diameter of the piston allow the interface with the tool to be maintained unvaried optimized to transmit the . striking energy, without modifying the tools and without increasing the axial dimensions of the breaker. This allows also to use yet existing tools for breakers known at the state of the art with pistons with the same weight.

As yet said, a fundamental element for the breaker performance is the accumulator. It has to be able to provide in active step the needed flow rate to pressurize the active thrust chamber, but it is important to make so that the variation between the maximum and minimum pressure is the lowest possible W so that the membrane is not stressed and to stabilize the functioning range of the breaker, thus avoiding too high pressure variations which have effect on the oil pump functioning. In fact, the greater the pressure under which the circuit works, the lower the flow rate supplied by the oil supplying pump. For this reason, it is ideal to work with a constant supplying pressure during all the cycle.

For this reason, according to a preferred embodiment of the breaker according to the present invention, even reducing the piston displacement of the breaker with respect to what known at the state of the art at equal force exerted by the breaker, there have been maintained accumulators with volumes similar to those traditionally used on breakers known at the state of the art. The ratio between the volume of the accumulator and the hammer piston displacement according to the present invention is preferably between 10 and 14, contrary to what known at the state of the art, in which such ratio is lower than 10.

Concerning the high pressure circuit in the breaker according to the present invention there have been adopted some measures to reduce the charge loss in the hydraulic circuit between the inlet of the breaker/accumulator and the inlet gap in the active thrust chamber. Such measures are:

- introduction of a chamfer (30) shown in figure 6, at the intersection between the duct (144) connecting the accumulator (14) to the active thrust chamber (11) and the duct (31) connecting the inlet (13) with the inlet gap in the active thrust chamber so that it is favoured the oil direction change avoiding the vortexes formation; - alignment of the inlet duct of the breaker (13) with the inlet duct (31) in the active thrust chamber, in order to reduce the deviations in the oil path connecting the inlet to the thrust chamber.

- increase in the area of the inlet gap in the active thrust chamber. In particular, the ratio between the area of the inlet gap and piston displacement is greater than 1.5E-02m^~1.

Also the low pressure circuit of the breaker according to the present invention is modified with respect to the known state of the art. The low pressure circuit is in fact connected to the high circuit through the ratio of the active and passive thrust areas of the piston. In passive step the piston is subject to the action of two forces acting in vertical direction. The first, which brings it again upwards is given by the product of the high pressure for the passive thrust chamber.

The other force is given by the product of the pressure in the active thrust chamber, which in this step is connected with the low pressure portion of the hydraulic circuit, for the active thrust area. Since the active thrust area is greater than the passive one, it follows that in order to make the piston go up again from PMI to

PMS the high pressure cannot be lower than a minimum value, in function of the ratio of the two areas multiplied for the pressure in the thrust chamber in this step. At the end of the active step the active thrust chamber is in connection with the high pressure. The distributor begins to go up and closes the high pressure. From now on until the moment in which it opens the discharge gaps there are generally 4-6 mm of stroke in which the distributor goes up and all the gaps are closed.

Such value cannot be brought to zero owing to the working tolerances and to considering the wear of the components in time. This means that the volume of such a chamber increases, owing to the difference between the outer upper and lower diameter of the distributor. Since the oil is not compressible, to such expansion corresponds a loss in pressure in the active thrust chamber. Theoretically, it can be reached also a lower pressure than the vapour tension, even if the pressure depends really also on inner drawings and by the air quantity dissolved in the oil. In any case, when the low pressure gap is freed it can happen that the pressure in the active thrust chamber is lower than the one of recirculation, therefore the chamber is pressurized almost instantly. However, in this step, the piston has yet began again its going up step, so when the active thrust chamber is pressurized, the force needed to make the piston go up again increases suddenly by a very great value, equal to the product of the ratio between the two areas previously cited for the pressure jump which occurred in chamber. This causes pressure oscillatory phenomena at the inlet detected on some breakers, and shown in figure 7.

The increase in high pressure gap at values greater than 1.5E-02m^~1 with respect to the piston displacement avoid the described inconvenient, for two reasons:

- during the active step the thrust chamber is better pressurized and so it reaches final higher

/'

pressure values, so also with the following expansion due to the distributor going up again, the final pressure will be higher and so near the one of recirculation;

- the increase in dimensions of the inlet gap in the active thrust chamber has reduced the length of the piston stroke during which all the gaps are closed. Such stroke can be considered approximately equal to 2mm. It follows that the expansion connected to a reduced stroke creates a lower pressure jump.

The low pressure circuit of the breaker according to the present invention eliminates the annular chamber around the piston. Referring to the figure 3, while the distributor goes down from PMS to PMI, the oil is first discharged through the primary discharge gap (50) and when this is closed through the secondary one (40) .

In the breakers known at the state of the art, the secondary gap (40) is normally closed by -the piston, but during the active step, while the piston goes down, at a certain point, the secondary gap is freed and put in communication with an annular chamber (42) obtained in the piston which in turn is in communication with the discharge. The oil reaches the discharge passing through a chamber

(42) obtained in the volume of the piston. Obviously this annular chamber is in movement since the piston is going down.

In the breaker according to according to the present invention, the secondary discharge gap (40) is directly in connection with the discharge, through an annular compensation chamber (41) obtained in the body of the breaker and not in the piston. In this way, the oil makes less road and the discharge loss is reduced. Therefore, lowering the average pressure at^' the discharge allows to lower the maximum inlet pressure avoiding that it reaches too high values. The compensation chambers are aimed at attenuating possible pressure peaks when the distributor begins again its going up. In this step, in fact, until the distributor does not close the high pressure gap, the low circuit is in communication with the high one through the secondary discharge gap. This step is very short (< 1 ms) , but it can be created a pressure peak in the low circuit. The compensation chambers serve to attenuate such peak.

Claims

1. Breaker for excavator (1) comprising:

a body (10) inside which it is obtained a hydraulic circuit which can be supplied from outside with liquid under pressure, said hydraulic circuit comprising:

an inlet (13) for the liquid under pressure;

an outlet (18) for the return of the liquid under pressure to the supplying circuit;

an active thrust chamber (11) with diameter (A) and a passive thrust chamber (20) ;

ducts (12, 21) to connect said active thrust chamber (11) and said passive thrust chamber (20) to said inlet (13);

- a piston (15) configured so that it can slide alternatively inside said breaker under the thrust of said liquid under pressure

characterized in that

said piston^' (15) is provided, at the active thrust chamber, with a projection with diameter (C) smaller than the diameter (A) of the active thrust chamber, said projection being wholly contained inside the active thrust chamber.

2. Breaker for excavator (1) according to claim 1, characterized in that said hydraulic circuit comprises a bypass between said hydraulic ducts (12, 21) which connect said thrust chamber (11, 20) to the inlet (13) of the liquid under pressure and the outlet .(18) of the hydraulic circuit configured so that said bypass, during the functioning of the breaker, is obstructed by the piston (15), and is freed when the piston (15) is in a position which is provided with an axial amplitude greater than a predetermined limit position, thus realizing a hydraulic circuit with reduced charge loss between the inlet (13) and the outlet (18) of said hydraulic circuit.

3. Breaker for excavator (1) according to claim 1 or 2, further comprising a tool (16) coaxially positioned to said piston (15) and configured to slide axially between a first and a second position. j,

4. Breaker for excavator (1) according to claim 3, further comprising a tool-stopper (21) integral with said metal body and characterized in that said first and second position are defined by the engagement of the ends (161, 162) of a groove (163) obtained in said tool (16) on said tool-stopper (21) .

5. Breaker for excavator according to any one of claims 2 to 4, characterized in that said bypass comprises an annular groove (22) concentric to the 2014/045264 piston (15) , communicating with said ducts (12, 21) to connect said active thrust chamber and said passive thrust chamber to said inlet (13) .

6. Breaker for excavator according to any one of claims 2 to 4, characterized in that said bypass comprises one or more holes provided in radial direction on the inner surface of the sliding seat of said piston (15), communicating with said ducts (12, 21) to connect said active thrust chamber and said passive thrust chamber to said inlet (13) .

7. Breaker for excavator according to any one of claims 5 or 6, characterized in that said piston (15), in working position, at the annular groove (22) or said holes provided in radial direction, is provided with a diameter (B) such that the piston (15) slides in the seat obtained in the body of the ^■breaker (1), and at the same time it is obtained a seal with respect to the annular groove (22) or the holes provided in radial direction on the inner surface of the sliding seat of the piston, and in that, said piston (15) has further a section with diameter (A) , smaller than said diameter (B) which is at said annular groove (22) or said radial holes when the axial amplitude of the piston is greater than said limit position, thus freeing said bypass 2014/045264 and putting in communication said inlet (13) with said return under low pressure of the oil (18) .

8. Breaker for excavator according to any one of the preceding claims, further comprising a distributor (17), positioned concentrically to the piston (15) and configured to slide axially putting in communication, alternatively, the active thrust chamber (11) with the portion of the hydraulic circuit under high pressure or with the portion under low pressure.

9. Breaker for excavator according to any one of the preceding claims, further comprising an accumulator (14) comprising a first volume (142) connected to said circuit containing the liquid under pressure and a second volume (141) separated from said first volume (142) by an elastic membrane (143) .

10. Breaker for excavator according to any one of the preceding claims, further comprising an annular chamber (41) in communication with the outlet (18) of the hydraulic circuit and arranged concentrically to said piston (15), which is put in communication with said passive thrust chamber (20) during the piston going down, thus allowing to discharge the oil from said passive thrust chamber at the outlet of the hydraulic circuit 2014/045264 characterized in that said annular chamber (41) is obtained in the metal body of said breaker.

11. Breaker for excavator according to claim 9, characterized in that the ratio between said first volume (142) of said accumulator (14) and the piston displacement of the breaker is preferably between 10 and 14.

12. Breaker for excavator according to any one of claims 9, 10 or 11, characterized in that at the intersection between the duct (144) connecting the accumulator (14) with the active thrust chamber (11) and the duct (31) connecting the inlet (13) with the active thrust chamber is provided a chamfer so that the oil direction change is favoured avoiding the formation of vortexes.

13. Breaker for excavator according to any one of the preceding claims, characterized in that the ratio between the area of the inlet gap in the active thrust chamber (11) and the piston displacement is greater than 1.5E-02m^_1.