EP4345216A1

EP4345216A1 - Breaker with optimized hydraulic circuit

Info

Publication number: EP4345216A1
Application number: EP23196588.0A
Authority: EP
Inventors: Alessandro De Luca
Original assignee: Tecna Group Srl
Current assignee: Tecna Group Srl
Priority date: 2022-09-27
Filing date: 2023-09-11
Publication date: 2024-04-03

Abstract

Breaker configured to be used with an excavator provided with a hydraulic circuit, said hydraulic circuit being provided with a delivery circuit for oil under pressure and a return circuit, said breaker comprising:- a piston (22A) configured to be moved with a reciprocating motion between a Top Dead Point and a Bottom Dead Point;- an inlet (2) for oil under pressure, connected to an active thrust chamber (21) where oil pressure pushes said piston (22A) towards the Bottom Dead Point and to a passive thrust chamber (13) where oil pressure pushes said piston (22A) towards the Top Dead Point;- a distributor (24), positioned around said piston (22A) and configured to be moved with a reciprocating motion between its own Top Dead Point and its own Bottom Dead Point, putting the active thrust chamber (21) alternately in communication with the inlet for oil (2) under pressure and with the annular discharge chamber (5),wherein said annular discharge chamber (5) is connected to at least two outlet holes (19, 20), configured to be connected, alternatively to each other, to said return circuit, said at least two outlet holes (19, 20) having different diameters.

Description

TECHNICAL FIELD

The present patent application for industrial invention relates to a breaker for excavator provided with an optimized hydraulic circuit, which can be applied to a wide range of excavators with various hydraulic features in terms of pressures and flowrates.

State of the art

A hammer for excavator is one of the various kinds of tools applied to excavators. The hammer is coupled to the hydraulic circuit of the excavator and commonly used to demolish rocky and cement material to carry out excavation.
A hammer is generally provided with a hydraulic circuit which, being supplied with oil under pressure, produces a reciprocating movement of a piston which, by hitting repeatedly on the hammer bit, allows the demolishing action. The piston reciprocating movement is obtained by means of a distributor which, by moving with a reciprocating movement inside the piston as well, allows the liquid under pressure to supply alternatively the various hydraulic paths realized in the body of the excavator hammer.
Various kinds of hydraulic circuits are known at the state of the art, which are mounted on excavators, and with which not only hammers but also other tools have to be coupled.
Hydraulic circuits had traditionally a pressurized oil return (with counter-pressures of about 10-15 bar, for excavators with mass up to about 10000 kg), and oil flowrate adjusted according to the maximum absorbable load logic. In this kind of circuits flowrate and pressure cannot be combined. With the working pressure increasing beyond a certain value, the oil flowrate decreases.
There are also known, and there have been introduced recently on the market, excavators whose hydraulic circuits have a pressurized oil return with counter-pressures of about 20-25 bar, high flowrates (typically greater even up to about 20% in comparison to the previous generations) and a logic of oil flowrate adjustment of "load sensing" kind. In these excavators flowrate and working pressure can be combined, and the flowrate never decreases with the increasing of pressure.
Moreover, there exist excavators with modified circuits, in which the oil return goes directly to the tank without counter-pressure (or, however, with typically lower counter-pressures, between 5 and 8 bar). Generally, this modification to the hydraulic circuits is not provided directly by producers, but it is often applied by users because most of hammers do not function well with high counter-pressures.

Technical problem

Therefore, there is the need to realize a hammer for excavator which can work efficiently with all the kinds of hydraulic circuits known at the state of the art.

Aim of the invention

Aim of the present invention is to provide a hammer for excavator which can work efficiently with all the kinds of hydraulic circuits known at the state of the art, and which does not need adjustment or calibration operations for its own usage.
In particular, a specific aim of the present invention is to provide a unique breaker able to be adapted to any kind of hydraulic circuit provided on an excavator, and so to function in a reliable way in a wider range of flowrates and counter-pressures.
Another aim of the present invention is to provide a hammer, which, without using valves, but with only two discharge holes and an optimized hydraulic circuit, is able to function in a wide range of discharge counter-pressures (5-25 bar) and flowrates, while guaranteeing better efficiency, high impact energy and lower working pressures.
Yet, another aim of the present invention is to provide a hammer provided with an automatic stop function which functions efficiently also with pressurized circuits (i.e. provided with high discharge counter-pressures) of the new excavators.

Brief description of the invention

The present invention realizes the prefixed aims since it is a breaker configured to be used with an excavator provided with a hydraulic circuit, said hydraulic circuit being provided with a delivery circuit for oil under pressure and a return circuit, said breaker comprising: a piston (22A) configured to be moved with a reciprocating motion between a Top Dead Point and a Bottom Dead Point; an inlet (2) for oil under pressure, connected to an active thrust chamber (21) where oil pressure pushes said piston (22A) towards the Bottom Dead Point and to a passive thrust chamber (13) where oil pressure pushes said piston (22A) towards the Top Dead Point; a distributor (24), positioned around said piston (22A) and configured to be moved with a reciprocating motion between its own Top Dead Point and its own Bottom Dead Point, putting the active chamber (21) alternately in communication with the inlet (2) for oil under pressure and with the annular discharge chamber (5), characterized in that said annular discharge chamber (5) is connected to at least two outlet holes (19, 20), configured to be connected, alternatively to each other, to said return circuit, said at least two outlet holes (19, 20) having different diameters.

Description of the figures

The invention will be described now with reference to the appended figures 1 to 11.
Figures 1 to 4 show the high/low pressure circuits and the drainage circuit of a breaker known at the state of the art; figures 5 and 6 show two vertical section views of a preferred embodiment of the invention; figure 7 shows a horizontal section view of the hammer according to the invention; figure 8 shows a detail of the discharge annular chamber; figure 9 shows a comparison between a piston known at the state of the art and the piston according to the present invention; figures 10 and 11 show circuits which allow the automatic stop function in the hammers known at the state of the art and in the hammer according to the invention.

Detailed description of the invention

Figure 1 describes the functioning principle of the breakers known at the state of the art.
The high-pressure supply circuit of the breaker comprises an inlet (2) for oil under pressure, connected to the active thrust chamber (21), and by means of the duct (9), to the passive thrust chamber (13). The circuit comprises also an outlet (4) for the oil return towards the hydraulic circuit of the excavator.
As it is shown in figure 9, the piston (22) is symmetrically shaped around a central axis and is provided with sections with different diameter (A, B, C, D). In particular, the discontinuity between the section with greater diameter (C) and the section with smaller diameter (D) is on the passive thrust chamber (13). The circular crown defined by the diameter discontinuity defines the surface on which the liquid pressure, provided in the passive thrust chamber (13), acts in axial direction, upwards, during the piston going up step.
The provision of the projection (221), inside the active thrust chamber, allows to fill at least partially the volume of the active thrust chamber, thus increasing the piston mass with equal breaker dimensions and displacement.
It is to be specified firstly that, with exception of the drainage circuit, which is made up by a unique path, the hydraulic circuit comprises identical ducts on three planes passing through the symmetrical axis of the hammer and offset of 120° to each other. In other terms, the hammer comprises, in addition to the section of figure 1, two identical sections more, except for the provision of the discharge holes.
The circuit known at the state of the art comprises an inlet for oil under pressure (2) and an outlet (4) .
By means of an annular thrust chamber (1), the oil arrives from the inlet (2) to a high-pressure circuit (9), which supplies the passive thrust chamber (13) and the chamber (131) for the start and stop functioning.
The hammer comprises further a low-pressure circuit, where from the discharge chamber the piston (7) and from the discharge circuit of the distributor (11) the oil arrives in a common intermediate discharge chamber (5) which is in turn connected to the discharge annular chamber (10) on which it is provided the unique discharge hole (4) (oil outlet of the breaker). The drainage circuit (17) connects the drainage chamber (18) to the discharge circuit of the distributor (3) in the point (16), and then both go in the annular discharge chamber (10) which is communicating with the oil outlet.
Figure 3 shows a detail of the discharge circuit of the distributor both when it goes up from its Bottom Dead Point (BDP) to its Top Dead Point (TDP) and when it goes down, in addition to the discharge circuit of the piston when it goes up again from BDP to TDP.
It is to be noted that the volume comprised between piston (22) and discharge is a volume of oil which is filled when the piston goes down, sucking oil from the return tube. This oil is sent again in the tube through the discharge when the piston goes up. This determines a pumping cycle which is an efficiency lost, calculated between 5 and 10% of the absorbed power.
As it is shown in figure 3, the device known at the state of the art comprises also a cylinder flange (23), positioned under the distributor (24). The inner diameter of the cylinder flange (23) is the diameter on which the high pressure (HP) acts when the piston goes down. The High Pressure acts in fact up on the piston (22) and on the cylinder flange (23), and down on the passive thrust chamber (area of passive thrust indicated with HP in figure 9) .
So, the force acting in thrust step on the piston is the product of the supply pressure (i.e. the High Pressure) for the difference between the inner area of the cylinder flange (23) and the area of the passive thrust chamber (13).
In going up step instead, in the active thrust chamber (21) is provided the Low Pressure (i.e. the discharge counter-pressure), while in the passive thrust chamber (13) there is the High Pressure.
In the piston known at the state of the art, shown in figure 9, the inner diameter of the cylinder flange is different from the diameter of the thrust chamber which makes the piston to go up again.
Figure 4 shows a short circuit (25) generated between the high-pressure circuit and the low one, when the distributor (24) begins to go up. In that moment in fact, in the high-pressure chamber (21) there is yet high pressure because the port of high pressure (210) is open, since it is not yet occluded by the distributor (24). The duration of the short circuit is very short, with times in the order of 1 ms, anyway sufficient to generate pressure waves propagating inside the whole low circuit, up to arrive to the oil retainers and which, also, act on the correct breaker working cycle, in particular by varying the counter-pressure which the piston has to win instantaneously to go up again from its BDP to its TDP.
To obviate these drawbacks, which cause a useless energy dissipation, a faster materials wear and functioning instability, the circuit of the hammer according to the present invention has been modified as described in the following.
Figures 5 and 6 show the high and low pressure circuit of the hammer according to the invention. In particular, figure 6 shows also the drainage circuit (10).
As it is specified concerning the hammer known at the state of the art, also in this case, except for the drainage hole (10) which remains single, the hydraulic circuit comprises identical ducts on three planes passing through the symmetry axis of the hammer and offset of 120° to each other. In other terms, the hammer comprises, in addition to the section of figure 5, two identical sections more.
The analysis of figures 5 and 6 allows to highlight some differences between the circuit of the hammer according to the invention and the circuit known at the state of the art.
One of the main differences is that there are no intersections between the various paths of the hydraulic circuit. For example, the holes (121, 122, 123) of the discharge circuit of the distributor (12) are realized in planes orthogonal to the symmetry axis of the piston (22), they are not connected to each other and communicate directly in the discharge annular chamber (5). In this way, the oil can flow in these discharge circuits (121, 122, 123) without meeting resistances due to other flows arriving in opposite direction.
The hammer comprises also two outlet holes (19, 20), with different diameter, which connect the discharge annular chamber (5) to the outside, and to which the return tube of the hydraulic circuit of the excavator can be connected. This is visible in particular in figure 7, which shows a section view of the hammer according to the invention on a horizontal plane at the height of the discharge chamber (5).
Conveniently the diameters of the two holes (19, 20) are calibrated so that it is possible the usage of the hammer with different hydraulic circuits.
For counter-pressures higher than 14-15 [bar] it is used the greater hole (20), by connecting the return tubes of the hydraulic circuit of the excavator thereto, and the smaller hole (19) is closed. For counter-pressures under this value it is used the smaller hole (19), and the greater diameter hole (20) is closed.
Another important difference, which can be observed in figure 5, is the absence of the cylinder flange, which was instead provided in the hammers known at the state of the art, as it is shown in detail in figures 3 and 4. The elimination of the cylinder flange allows to gain efficiency since it is eliminated the pumping cycle, caused by the short circuit of the high pressure with the discharge occurring at each cycle with the piston known at the state of the art.
Figure 8 shows the discharge circuit of the distributor according to the present invention.
As it can be observed in figure 6 and figure 7, the discharge circuit in the piston going up step is made up of a plurality of straight paths (121, 122, 123) oriented in radial directions, which lead directly and without bends or deviations to the discharge annular chamber (5).
Preferably, as it is shown in figure 7, there are provided three discharge holes (121, 122, 123); in other embodiments there are provided 4, 5 or 6 discharge holes.
The device comprises also an inner discharge annular chamber (13), which is normally obstructed by the piston.
As it is explained in detail in the following, said annular discharge chamber is obtained by a narrowing (22A3) of the diameter of the piston (22A) .
During the going up step of the piston (22A), as it is visible in detail in figure 8, the discharge circuit (15) is opened by the piston a little before reaching its TDP, and it remains open for the whole duration of the going down of the distributor (24) up to reach the BDP.
Moreover, when the distributor (24) starts from the Bottom Dead Point to reach the Top Dead Point, the circuit of the discharge annulare chamber (13) is closed and so the short circuit is not generated, which, for the hammers described at the state of the art, is visible in figure 3. In this way, the critical section for the oil passage, since short circuits and flow intersections are eliminated, remains only the discharge hole, and by variating its dimension it is possible to control the inner counter-pressure which the hammer generates as a function of its flowrate.
In the following, there are described a series of features of the piston (22A) to be used with the hammer according to the invention, which are functional to modify the hammer displacement and the ratio between thrust areas in the piston going up step.
With reference to figure 9, it is shown a comparison between a piston (22) known at the state of the art and a piston (22A) according to the invention, of equal weight.
As it is shown in figure 9, the piston (22A) according to the invention is an axial-symmetrical solid comprising:

a projection (22A1) which, when the hammer is assembled, is positioned inside the active thrust chamber;
the projection 22A1 has conical shape to favour the expulsion of oil from the active thrust chamber when the piston goes from BDP to TDP in going up step,
a second portion with greater diameter (22A2), having constant diameter and interrupted only by the discharge annulare chamber (22A3), obtained by means of a reduced diameter section;
a terminal portion (22A4) configured to hit the tool during functioning.

Unlike what just described, in the pistons known at the state of the art there is no discharge annular chamber (22A3), and the discharge circuit is obtained by using the previously described cylinder flange (23).
By eliminating the cylinder flange (23), thanks to the provision of the reduced diameter section (22A3), it is eliminated the provision of the pumping volume, with estimated efficiency increase between 5% and 10%.
During the piston going up step from BDP to TDP, the high pressure always acting on the passive thrust surface (AP), shaped as circular crown, has to win the piston weight force (which, generally, for hammers up to 400 kg is almost negligible) and the force exerted by the discharge pressure. The discharge pressure acts, with reference to figure 9:

for pistons of the kind known at the state of the art on the sum of the active thrust (AA) and pumping areas (AG);
for the piston according to the invention on the sole active thrust area (AA).

The ratio between the area on which the discharge pressure acts and the passive thrust area is defined as "ratio between the thrust areas" (K), and it is the factor determining the functioning minimum pressure of the breaker. So, it results:

Pistons known at the state of the art: K = (AA+AG)/AP
Piston according to the invention K = AA/AP

The minimum pressure (p_min) at which the piston will start to go up is given (not considering in first approximation the piston weight force) by: $p_\min = k * (Cp + Dp_int)$
Where

Cp is the discharge counter-pressure,
Dp_int are the inner charge losts.

Since last generation excavators have circuits with counter-pressures (Cp) over 20 bar, it was needed to lower the k ratio from values generally greater than 7, provided in the hammers known at the state of the art, to values lower than 5.8.
In this way, it is reduced the effect the counter-pressure cp exerts on the functioning minimum pressure of the hammer.
Moreover, it is to be noted that the active thrust area (AA), since the pumping volume is eliminated, is very much greater in the piston according to the invention in comparison to the embodiments knonw at the state of the art.
So, with equal working pressure the force applied on the piston in going down step increases, so its acceleration increases and as a consequence the energy with which it impacts on the tool.
It is suitable to specify that the high pressure acts on the active thrust area (AA) in going down step, the low pressure in going up step (i.e. counter-pressure + losts), while only the high pressure acts on the passive thrust area (AP) in each step.
It is now to be considered that the displacement of the breaker can be calculated as the product of the piston stroke for the active thrust area (AA). Since the active thrust area is increased, with equal stroke the piston according to the invention would have a very much greater displacement in comparison to the the pistons known at the state of the art, and so, with equal oil flowrate, a very much lower working frequency (the working frequency is calculated in fact as the ratio between oil flowrate and displacement).
To obviate this problem the hammer according to the invention is configured to use very short strokes.
As a pure indication, for hammer of 120 kg the stroke is in the order of about 20 mm, and for hammers of 400 kg, of about 30 mm.
Moreover, increasing the active thrust area (AA) allows to work at lower inlet pressures in comparison to pistons known at the state of the art (about 20 bar less), even maintaining an impact energy equal to the previous version, in addition to gain efficiency because of the absence of pumping volume.
This helps also the excavators of the previous generation, since by working with lower pressures they will give more flowrate anyway in comparison to when with the current series they work with higher pressure but with less oil, because it is reduced by the control system.
This advantage compensates further the frequency reduction due to the displacement increasing.
Another advantage of the reduced stroke is the reduction of the piston average speed (which is equal to the product of two times the stroke for the number of revolutions) with advantages for the reliability and the seal of oil retainers.
So, in comparison to what known at the state of the art, the hammer according to the present invention is characterized by:

reduced K ratio (< 5.8)
great active thrust area (AA)
very small piston stroke.

In the following, it is described the automatic stop mode functioning of the hammer according to the invention.
With reference to figure 10, the automatic stop circuit of the hammer comprises a bypass port (20), connecting the high and low pressure circuit and which is released by the piston when it goes down beyond the BDP. This occurs when the user lifts the hammer (or when the tool breaks the rock and, so, it remains "hanged" in absence of outer resistance).
In this case, the high and low circuits are voluntarily put in communication and the hammer stops, avoiding idle blows on tool-stops.
Anyway, in some cases (and typically in the soft materials working) the piston too often tends to arrive in the automatic stop position (because there is no sufficient opposition by the material) and this slows down the working.
To avoid this kind of drawbacks at the state of the art there are used hammers not provided with bypass port, and so, which have no automatic stop function.
Anyway, since on the hydraulic circuits of the excavators of new generation it is often provided a solenoid valve closing the discharge when the user interrupts the oil supply, it happens that the oil return circuit goes under pressure even up to 70 bar, when the user interrupts the oil supply to the breaker.
These conditions make difficult the repositioning of the piston in its correct position; the force required is high, and sometimes the only way is to turn off the excavator, or to turn on the control hydraulic circuit of other tools, such for example the drill, to make the pressure on the return reduce.
To obviate this inconvenient, the hammer according to the invention comprises a bypass circuit for the modified automatic stop, as it is shown in figure 11.
All the hammers have a piston braking system, comprising a damping chamber (19) which avoids the impact of the piston at the end of the stroke with the cylinder, if it is actuated without the tool.
In the hammers known at the state of the art (see figure 10) the bypass port (20) is released before the piston comes in the damping chamber (19).
With reference to figure 11 instead, in the hammer according to the invention, there is no bypass port for automatic stop, but it is used the discharge circuit in the going down of the distributor.
In fact, the piston (22A) is configured so that, when the portion with greater diameter (22A2) comes in the volume of the braking window (14), since this is a closed volume except for the clearances between piston and cylinder (which are in the order of hundreths of millimeter), the immediate pressurization of the same stops the piston almost instantaneously.
The short circuit between high and low pressure can be realized only after that the piston has come in the damping chamber with a depth between 2.5 and [mm], so to release the discharge holes of the distributor.
In any case, at this point the pressure in the damping volume is so high that the piston bounces back thus restoring the normal functioning cycle.
In brief, it is changed the functioning logic.
In the pistons known at the state of the art, the start & stop sistem was the first protection system from idle blows, and the damping system intervened as back-up.
In the piston according to the invention, it is the damping system the primary sistem, and at equal weight of hammer, in the series TB it is anticipated in comparison to the series T (i.e. the piston has to do less stroke before actuating it), while the start & stop is only one solution which works in combination with the braking system, intervening after that the piston has come between 3 and 5 [mm] in the damping volume and favouring a rapid going up since it depressurizes the thrust chamber acting on the piston.

Claims

Breaker configured to be used with an excavator provided with a hydraulic circuit, said hydraulic circuit being provided with a delivery circuit for oil under pressure and a return circuit, said breaker comprising:
- a piston (22A) configured to be moved with a reciprocating motion between a Top Dead Point and a Bottom Dead Point;

- an inlet (2) for oil under pressure, connected to an active thrust chamber (21) where oil pressure pushes said piston (22A) towards the Bottom Dead Point and to a passive thrust chamber (13) where oil pressure pushes said piston (22A) towards the Top Dead Point;

- a distributor (24), positioned around said piston (22A) and configured to be moved with a reciprocating motion between its own Top Dead Point and its own Bottom Dead Point, putting said active thrust chamber (21) alternately in communication with the inlet for oil (2) under pressure and with the annular discharge chamber (5),
characterized in that said annular discharge chamber (5) is connected to at least two outlet holes (19, 20), configured to be connected, alternatively to each other, to said return circuit, said at least two outlet holes (19, 20) having different diameters.
Breaker according to claim 1, characterized in that said piston comprises a projection (22A1), positioned inside the active thrust chamber (21) with conical shape apt to favour the oil outflow when the piston goes from BDP to TDP during its going up.
Breaker according to one of the preceding claims, further comprising an inner discharge annular chamber (13) and a discharge circuit comprising three holes (121, 122, 123) realized in planes orthogonal to the symmetry axis of the piston (22A), not connected to each other and configured to put said inner annular discharge chamber (13) in communication with said annular discharge chamber (5).
Breaker according to claim 3, characterized in that said inner annular discharge chamber (13) is obtained by means of a narrowing (22A3) of the diameter of said piston (22A).
Breaker according to claim 4, characterized in that said piston (22A) is an axial-symmetrical solid comprising:
- a projection (22A1) which, when the hammer is assembled, is positioned inside the active thrust chamber (21);

- a second portion with greater diameter (22A2), having constant diameter and interrupted only by the annular discharge chamber (22A3), obtained by means of a reduced diameter section;

- a terminal portion (22A4) configured to hit the tool during functioning.
Breaker according to claim 5, further comprising a braking chamber (14), configured so that when the portion with greater diameter (22A2) comes in said braking chamber (14), said braking chamber (14) becomes a volume closed and filled with oil, whose provision avoids the further advancement of said piston.