EP0426928B1

EP0426928B1 - Method to automatically adjust the functional parameters of a percussion apparatus

Info

Publication number: EP0426928B1
Application number: EP89830451A
Authority: EP
Inventors: Mauro Vitulano
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-10-18
Filing date: 1989-10-18
Publication date: 1997-06-25
Anticipated expiration: 2009-10-18
Also published as: DE68928143T2; EP0426928A1; DE68928143D1; ATE154774T1; ES2103711T3

Abstract

The device exploits the striking mass rebound energy, which depends on the hardness of the material on which the tool operates. It is based on the functioning of the device as in the European Patent No. 0085279, and in providing adequate means to vary the distributor stroke during the piston upward-moving phase, as to anticipate or to postpone the percussion phase when the tool operates respectively on a less or more hard material. In this first case, the anticipation of the percussion stroke causes a decrease in the volume of the cylindrical chamber where the pressurized oil works and therefore, under the same power, it causes an increase in the blows frequency, if the working oil flow mantains unaltered.

Description

The present invention is applied to percussion hydraulic appliances used in both the demolition of very hard materials -such as concrete, reinforced concrete, rocks, frozen surfaces, etc. - and the digging of particularly hard soils, mine marking and extraction, etc.
In particular, it refers to those devices which - checking the high-pressure oil inlet and low-pressure oil outlet of a hydraulic apparatus - bring about the alternate movement of the mass striking the tool.
As well known, the alternate movement of the piston which strikes the tool in a hydraulic apparatus or by incompressible fluid, is obtained with a distributor which alternately places the chamber over the piston, in communication with a high-pressure circuit to give it impact power, and with a low-pressure circuit to bring the piston back to the upper dead centre.
The movement towards this dead centre is caused by the pressure exerted by the high-pressure oil itself on the piston annulus-like shaped surface 3d1, opposite to the wider circular surface 3b which receives the working push: the latter is greater than the former, due to the wider surface on which the high pressure is exerted.
The commonest distributor consists of a cylindrical tubular component whose external diameter - with the adequate tolerance margin - is equal to the internal diameter of the cylinder where the piston moves: along its circular lower edge, it is connected to a ring like flange, which runs vertically into a cylindrical chamber 2 coaxial to the cylinder, within the limits prefixed by the height of the same cylindrical chamber.
In some appliances, the distributor internal diameter is smaller than the piston head external diameter; in others, the internal diameter is equal to the piston head external diameter, as in the European Patent No. 0085279 by the same applicant.
In this case the piston head, instead of striking the opposite lower end of the cylindrical distributor, moves inside it, in the opposite direction: in this case, the difference between the diameter of the cylindrical chamber and that of the piston is twice the distributor radial thickness.
A common drawback to all the devices causing the piston alternate movement is the lack of capability to adapt in real time the striking rate and power per blow to the hardness of the material to crumble.
In order to avoid such drawback, some manufacturers conceived some particular devices which guarantee the blows frequency and power automatic variation according to the hardness of the materials to crumble - c.f. FR-A-2509217.
The apparatus as described in French Patent (see figures) is endowed with a cylindrical distributor 10 to close and open the inlet and outlet ports 6 and 7 of the high and low-pressure respectively, which limits the upward movement of the piston head when the latter comes into contact with the lower border of the distributor itself.
Therefore, the piston displacement is constant, i.e. it does not depend on the back-pressure caused by the rebound of the piston determined by the various degrees of hardness of the material to crumble.
For this aim, see figures of said French Patent Application, the device causing the striking mass 2 alternate movement also includes a unidirectional valve 22 which guarantees the fluid passage from the high-pressure circuit towards the cylindrical chamber over the piston and devices which guarantee a quick, subsequent displacement of the distributor 10 so to rapidly interrupt the connection with the high-pressure circuit 12 and to slowly connect the chamber 11 placed over the piston with the low-pressure circuit 13.
Thus, as the unidirectional valve permits the passage of the ultracompressed fluid into the cylindrical chamber over the piston, in the fraction of time during which this chamber is isolated from both the low-pressure and the high-pressure circuits, the maximum retrieval of reaction energy should be possible; the piston greater reversal velocity would cause - for a given oil supply - a shorter duration of every cycle of the apparatus, as well as an increase in the impact pressure, parallel to the increase in blows frequency.
In other words, such a device would cause an increase in blows frequency and impact power, which would be higher if the material to crumble is harder, without calling for a greater power i.e. a greater pressure of the oil to the digger or the shovel coupled to the apparatus.
Vice-versa, on a softer soil, the striking mass would work at a low velocity with a low impact power.
Such working method is irrational, as the breaking of scarcely compact soils should have a low velocity, although needing a smaller impact power: in other words, and contrarily to any logic, by means of this apparatus, concrete, rocks and very hard materials would be crumbled more rapidly than normally-compact soils.
Moreover, although the apparatus where the above-mentioned device is applied, absorbs reaction energy, it still undergoes high stresses owing to the incompressibility of the fluid.
The fact that this device increases rather than decreasing impact power and working velocity when the hardness of the material to crumble is greater, provokes a rapid wear of the tools.
The aim of this invention is to adapt in real time the power and frequency of a percussion apparatus to the hardness of the material where it works, avoiding the above-mentioned drawbacks caused by the apparatus as in the FR-A-2509217.
This invention - as characterized by our claims - solves the problem to vary the piston impact energy in real time, in inverse function to the blows frequency, so to adapt the latter to the resistance of the material to crumble, without varying the hydraulic power averagely absorbed by the apparatus, i.e. the absorbed power.
More specifically, this invention solves the problem of working on very hard materials such as rocks, concrete, etc., at lower frequency and higher impact energy and - on less hard materials - at greater frequency and lower impact energy.
The advantages obtained through the present invention mainly consist by the fact that the supplied power maintains on an average constant and that therefore the strains that the apparatus undergoes when working on very hard materials, and the consequent wear of the tools are smaller.
Moreover the apparatus requests a smaller working and maintenance expenditure, and operates by a greater velocity on less hard materials.
One way of carrying out the invention is described in detail below with references to drawings which illustrate only one specific embodiment, in which:

fig. 1.shows the device in the stroke-end position it gets when the percussion appliance works on soft materials;
fig. 2, shows the device in the stroke-end position it gets when operating on very hard materials;

fig. 3 shows the apparatus with the piston at the upper dead centre when the rebound energy is feeble, at the moment when the percussion stroke starts;
fig. 4, shows the appliance with the piston at the upper dead centre when the rebound energy is strong, at the moment when the percussion stroke starts;
fig. 5, shows the apparatus with the piston during the percussion phase and the distributor moving upwards to obstruct the high-pressure oil inlet port;
fig. 6 shows the apparatus with the piston at the lower dead centre;
fig. 7, shows the apparatus with the piston moving upwards;
fig. 8, the anticipation of the piston approach to the distributor when the rebound energy is feeble;
fig. 9, the apparatus with the piston at its approach to the lower border of the distributor when the rebound energy is strong: the distributor is in the stroke-end position;
fig. 10. the upper dead centre when the rebound energy is feeble;
fig. 11. the upper dead centre when the rebound energy is strong.

As illustrated in figures 1 and 2, the invention consists in the combination of the means forming the distributor as in EP-A-85279 by the same applicant, with devices limiting the distributor upward movement during the piston upward stroke, so that the piston start of percussion is anticipated when compared to the upper dead centre, when the material hit by the tool is scarcely hard, whereas, when the material is very hard -i.e. rocks, concrete, etc. - the piston start of percussion occurs exactly at the upper dead centre: the upper dead centre is fixed by stop corner 16 of the piston.
As in the EP-A-85279, the distributor is made up of a cylindrical tubular component 1, one of whose ends is connected to a flange-type ring plate, which can move with the protruding part la having width d1, in a ring chamber having height h and width d1, equal to the width dl of the flange protruding part.
The upwards movements of distributor 1 are caused by differences in pressure on faces 1b and 1c of distributor itself, during the down stroke of piston, the downwards movements of distributor solely by the pressure on face 1b during the up stroke of piston: this is possible because, during the upward movement, piston 3, whenever the contact occurs between its circular edge 3a and the distributor circular edge 1d. compresses the oil of the cylindrical chamber 4 which is placed over the piston surface 3b, provoking the distributor downward movement, whereas during the blow, when the distributor is in the positions showed in figures 5 and 6, the piston provokes the distributor upward movement when the latter circular edge 3 - moving downwards - protrudes from the distributor cylindrical cavity and goes beyond its edge Id, due to the effect of high pressure on the distributor edge 1c.
The annular grove 5, coaxial to the axis of the cylindrical chamber where the piston moves during the downstroke of piston, allows the oil under pressure to push on the distributor face 1c, having width d3, greater than the one of face 1b whose width d2 is smaller then d3, provoking its upward movement: this is made easier because the basis of the ring grove 2 gives a stop edge 2a having width d4, so that d3 - d4 > d2.
Duct 9 at the bottom of the tubular chamber 2, being connected to the low-pressure circuit, aims at creating the differences in pressures necessary to permit the downward movement of the distributor when the high-pressure oil inlet ports 7a must be opened.
Now the above-mentioned means are combined with devices permitting different velocities of the oil discharge from the annular chamber 2c of the tubular chamber 2, which the protruding ring 1a of the distributor 1 forms in the upper part of said tubular chamber 2.
These devices are made up of a controlled duct 11 having a small diameter or, in general, of a duct where a pressure valve 11.1 is inserted, which connects chamber 2c to exhaust duct 10, to bring about an exhaust velocity proportional to the pressure exerted by the distributor protruding ring la, that also depends on the piston rebound energy and velocity.
If the rebound energy is low, the distributor 1 cannot get the stroke-end fixed by the upper annulus-like shaped border 2b of the tubular chamber 2, that is, it does not run the entire height h of said chamber; therefore, the piston circular edge 3a anticipately touches the distributor circular edge 1d, so that the latter can move downwards, anticipately reopening the high-pressure oil inlet ports 7a: this brings about a decrease in the piston percussion stroke and, consequently, a decrease in the displacement, i.e. the volume of the cylindrical chamber where the pressurized oil operates, in order to push the piston downwards.
By firm absorbed power, this decrease in volume corresponds to an increase in the piston blows frequency.
Indeed, as the hydraulic power transmitted to the piston is equal to the oil flow Q multiplied by oil pressure p, i.e. (Q x p), if the pressure and oil flow remain firm and if the volume of the cylindrical chamber - where the pressurized oil operates - decreases, an increase in the piston blows frequency takes place.
When the piston rebound velocity, caused by a greater hardness of the material to crumble, is higher, the impulse determined by its momentum provokes a greater pressure on the distributor, which obliges the oil contained in the ring chamber 2c to completely flow, through the controlled duct 11, into the low-pressure circuit, and the ring 1a of the distributor to approach the upper ring surface 2b of the tubular chamber 2 itself.
This delays the approach of the piston circular edge 3a to the distributor circular edge 1d, and obliges the piston to reach a higher position before sealing the inner volume of the distributor 1, and provoking the distributor 1 downwards displacement, necessary to obtain the re-opening of the high-pressure oil inlet ports.
The piston upward greater stroke provokes an increase in the volume of the cylindrical chamber 4 where the pressurized oil operates to push the piston downwards and, consequently, an increase in the push that the high-pressure oil exerts on the piston face 3b.
This determines a greater energy in the blow transmitted to the tool and, if the power absorbed by the apparatus remains constant, a decrease in the blows frequency, i.e. the application of a greater percussion energy during a longer time.
The device also includes a maximum pressure valve 12, which discharges the oil into the high-pressure circuit if the piston rebound energy exceeds certain limits, so to further compress the gas contained in the accumulator 13 (i.e. nitrogen) through membrane 13a.
Valve 12 also works as a safety valve.
Figures 3 to 11 show the application of the devices according to the invention to the percussion apparatus according to EP-A-85279.
As we can observe in the above figures, the device according to the invention can be applied only to apparatuses of the type described in EP-A-85279, i.e. to apparatuses where the distributor 1 moves to open or to close the high-pressure oil inlet ports 7a and the low-pressure oil discharge ports, only as an effect of the pressures transmitted, through the piston movements, to the distributor ring faces 1b and 1c.
In particular, it can be applied to a percussion apparatus where the distributor moves in the opposite direction of the piston which slides coaxially inside it, that is downwards to open the high-pressure oil inlet ports 7a immediately after the approach of the upward-moving piston circular edge 3a to the distributor circular edge 1d or, alternatively, upwards to close these ports 7a when, during the percussion stroke, the piston circular edge 3a passes the distributor circular edge 1d.
The height h of the tubular chamber 2 depends on either a greater or a smaller stroke allowed to the distributor 1; similarly, the controlled duct 11 section, or the pressure valve replacing its function, must be chosen according to the performance desired by the apparatus.
As shown in figures 3 to 11, the mechanical stroke-end 16 limits the piston upwards maximum stroke.
The push for the piston upward movement is permanently applied on the annulus-like shaped surface 3d1 having width s, and it has an effect only when the high-pressure oil inlet ports 7a are closed.
C1 and c2 indicate the axial length of the chamber 4, in the case of a soft or a hard material, respectively.
The hydraulic hammers manufactured according to the invention do also involve some important advantages.
The impulse which the piston receives during its return stroke from the material to crumble (according to its degree of hardness) provokes a higher or lower upward-stroke velocity of the piston itself which not only causes, respectively, an advance or a delay in the approach of the edge 3 of the piston head to the distributor lower circular edge 1d, but also gives it a higher or lower degree of kinetic energy intensity: said energy, by causing an accordingly proportioned extra-movement of the distributor 1, allows the recovery of the rebound energy without requiring an increase in the power absorbed by the apparatus.
In fact, the head of the piston, after getting into the distributor, slides according to the intensity of the rebound energy, so allowing the high-pressure fluid to recover said energy.
Furthermore, the recovery of the rebound energy takes place without interfering with the frequency of the piston blows, i.e. if the material to crumble is hard, the recovery of the rebound energy takes place with a lower frequency of the piston blows, whilst, if said material is softer, the recovery of the rebound energy takes place with a higher frequency of the piston blows.
Another advantage of the invention lies in the fact that, by completely closing the duct 11, it is possible to obtain a still higher frequency of the piston blows and a lower impact energy; on the contrary, by completely opening the duct 11, it is possible to obtain a still lower frequency of the piston blows and a higher impact energy.

Claims

"Method to automatically adjust the functional parameters of a percussion apparatus to the hardness of the material to crumble", said percussion apparatus being of a hydraulic type and being provided with a cylindrical chamber (4) wherein a cylindrical tubular distributor (1) oiltightly and alternatively slides to allow the high-pressure fluid being thereto introduced, through the inlet ports (7a), to give the piston its impact power, and to discharge the low-pressure fluid into the low-pressure circuit through the duct (10) during the upward sliding motion of the piston towards the upper dead centre, the piston head (3) oiltightly sliding inside the cylindrical tubular distributor (1) in opposite direction and alternatively, the distributor (1) being provided, along its lower circular border, with an external ring (1a) which is forced to alternatively slide along a tubular chamber (2) having height h and coaxial to the cylindrical chamber (4), the ring (1a) being provided with a horizontal annulus-like shaped face (1c), to cause, by means of the high-pressure fluid, the upward sliding movement of the distributor (1) as the piston head (3) comes out of said distributor during its downward movement, to close said high-pressure fluid inlet ports, the function of duct (9) at the bottom of the tubular chamber (2) being of discharging the oil therein contained into the low-pressure duct (10) during the downward sliding movement of the distributor (1) so as to permit the re-opening of the high-pressure inlet ports (7a) as the piston head approaches, with the edge (3a), the edge (1d) of the distributor, characterized in that the position of said distributor is controlled by a gauged duct (11) admitting fluid pressure from the low-pressure duct (10) to an annular chamber (2c) adjacent the rearward end of the ring (1a) of the distributor (1), according to both the high-pressure and the back-pressure produced by the rebound of the piston, so as to advance or delay, during the upward movement of the piston itself, the approach of the edge (3a) of the piston head (3) to the lower edge (1d) of the distributor, to cause the downward movement of the distributor (1) itself and the consequent re-opening of the inlet ports (7a) of the high-pressure fluid.
Method according to claim 1, characterised in that the duct (11) contains further a pressure valve (11.1).
Method according to claims 1 or 2, characterised in that the effect of the gauged duct (11) is such that the volume of annular chamber (2c) is varied to a minimum when working in hard rocks and to a maximum when working in soft rocks.
Method as in previous claims, characterized by the fact that the advanced or delayed approach of the upper edge (3a) of the piston head to the distributor lower edge (1d) brings about a variation in the dead upper centre position and, respectively, a decrease or an increase in the cylindrical chamber volume determined by the piston head during its sliding movement from the dead upper centre to the dead lower centre, i.e. a decrease or an increase in the piston displacement of the apparatus.
Method as in claims 1, 2, 3, 4, characterized by the fact that, by firm absorbed power, as a result of a decrease in the piston displacement, the piston blows frequency increases and the impact energy decreases.
Method as in claims 1, 2, 3, 4, characterized by the fact that, by firm absorbed power, as a result of an increase in the piston displacement, the piston blows frequency decreases and the impact energy increases.
Method as in previous claims, characterized by the fact that the distributor (1) may assume according to the rebound pressure any functional positions between the annulus-like shaped borders (2a) and (2b) of the tubular chamber (2).
Method as in previous claims, characterized by the fact that the high-pressure chamber is endowed with a pressure-limiting valve (12) to discharge the oil into the high-pressure circuit, as the piston back-pressure exceeds safety limits.