Abstract:
Two working pistons (AK 1 , AK 2 ) strike on the anvil ( 10 ) of a drill device or a rock breaking device. One working piston (AK 1 ) is a solid piston, while the other (AK 2 ) is an annular piston. Both working pistons can work at the same or substantially the same rate. In general, the percussion rate acting on the anvil ( 10 ) can be doubled with two working pistons. The working pistons can be controlled in common or independent from each other. In a synchronous mode with equal phase, the impact energy is multiplied; in an asynchronous mode or a mode with opposite phases, the percussion rate is increased.

Description:
BACKGROUND OF THE INVENTION 
     The present invention refers to a method for performing work in the ground or on rock, where impacts are dealt on an anvil by a hydraulically driven working piston, as well as to a hydraulic percussion device for performing such work in the ground or on rock. 
     The term work in the ground or on rock refers to drilling in the ground or in rock, in particular to impact drilling; among others, this also includes superposed drilling with an inner drill column and an outer drill column, as well as the operation of rock breaking devices wherein a working tool in the form of a chisel is driven into rock by percussion, so as to break the rock. 
     Hydraulic percussion devices are known that strike on the adapter end of a pipe column for drilling work or on the chisel of a rock breaking device. The efficiency of such a percussion device depends on the energy of the single impact and on the percussion rate. A high single impact energy is achieved if the working piston of the percussion device has a great mass. To accelerate such masses, high pressures are required. In practice, the mass of the working piston is several kilos and the piston stroke is 35 mm, for example. Typical piston rates are 7 to 11 m/sec. The achievable percussion rate is between 250 and 3,500 impacts/min. If the single impact energy is to be increased, it is common to increase the mass of the working piston, which, however, generally results in a decrease of the percussion rate. 
     From German Patent 43 43 589 C1, a fluid operated impact drill is known, wherein the working piston is controlled by a control piston and strikes on the adapter end of a drill column. In order to free the drill column when withdrawing the drill column, a back stroke piston is provided that strikes on a counter strike surface of the adapter end opposite the anvil. Here, the back stroke piston is activated only when the working piston is deactivated. 
     It is the object of the present invention to provide a method for performing ground or rock work and a hydraulic percussion device to achieve a higher efficiency of the percussion work, i.e. an increased drill advancement or a higher breaking efficiency (in rock breaking). 
     SUMMARY OF THE INVENTION 
     The present method and hydraulic percussion device provide for at least two working pistons striking in the same direction on an anvil. Thus, the anvil is acted upon by two working pistons, the impacts dealt by the working pistons preferably being offset in time. This results in an increased percussion rate without the single impact energy being lowered by a reduction of the piston mass. 
     Basically, the pistons are intended to strike the anvil at different times. The movements of the working pistons can be synchronized such that the working pistons are operated with mutually offset phases, so that two working pistons would be phase-shifted by 180°, for example. This means that one working piston performs the impact stroke while the other piston performs the return stroke. In another alternative, the two working pistons operate independent from each other and at different rates. Here, it is assumed that the impacts of the working pistons are normally offset in time and that the both working pistons happen to strike concurrently only at certain moments. 
     Another variant of the invention provides that the impacts from the working pistons are dealt synchronously, i.e. at the same time. In this case, the working pistons have to be operated at the same working rate and without mutual phase shift. It is also possible to provide a percussion device such that the working pistons can optionally be operated synchronously and asynchronously. 
     The invention provides for a high number of impacts (percussion rate), whereby the drill column is kept in constant movement (vibration) during drilling. Since most grounds contain an amount of grainy material that is caused to move by the high number of impacts, a very great drill feed is achieved in percussion drilling. Furthermore, the present method is adapted to prevent bouncing impacts that occur when an impact meets a shock wave traveling back along the drill column. Due to high number of impacts, the next impact is always performed already when the returning wave has not yet reached the rear end. 
     The present invention allows for numerous variants of control for the at least two working pistons. Both working pistons may be controlled separately and completely independent from each other. Alternatively, a control is conceivable where both working pistons are equal or a control, where one working piston functions as a master and the other functions as a slave. 
     In the context of the present invention, the impacts on the anvil are dealt by different working pistons. Preferably, the working pistons have substantially the same mass. That means that difference between the masses is 10% at most. However, the masses may differ more, yet the mass of the lighter working piston should not be less than two thirds, preferably not less than three quarters of the mass of the heavier working piston. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following is a description of the preferred embodiments of the present invention with reference to the accompanying drawings. 
     In the figures: 
     FIG. 1 is a schematic view of a first embodiment of the percussion device with independently controlled working pistons, 
     FIG. 2 illustrates an embodiment, where the working pistons control each other, 
     FIG. 3 illustrates an embodiment, where one working piston cooperates with one control piston, thereby controlling the other working piston, 
     FIG. 4 illustrates an embodiment, where one working piston cooperates with a control piston, while the control piston simultaneously controls the other working piston, 
     FIG. 5 an embodiment similar to FIG. 4 but with a switching element added, with which one of several modes may be selected, one of the modes being illustrated in FIG. 5, 
     FIG. 6 the switching element of FIG. 5 in a second mode, and 
     FIG. 7 the switching element of FIG. 5 in a third mode. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In all embodiments, the anvil  10  is the adapter end of a drilling device, the adapter end being connected to a drill column (not illustrated) having a drill bit at its front end. The inset end comprises a splined shaft section  11  engaged by a rotary drive (not illustrated) so as to rotate the inset end, whereby the drill column is also rotated. 
     At its front end, the anvil  10  has a first anvil surface  12  and a second anvil surface  13  spaced therefrom. A shaft  14  projects rearward from the anvil surface  13 . The first anvil surface  12  is provided at the end of the shaft  14 . 
     As illustrated in FIG. 1, the first anvil surface  12  is struck by a first working piston AK 1  displaceable within a working cylinder AZ 1 . The working piston AK 1  is controlled by a control piston SK 1  displaceable within a control cylinder SZ 1 . The control piston SK 1  is a hollow control sleeve, whereas the working piston AK 1  is a solid piston. 
     The control cylinder SZ 1  is traversed by a high pressure line HD through which a medium is supplied at high pressure. The hydraulic medium also fills the hollow interior of the control piston SK 1 , A high pressure line  15  leads from the control cylinder SZ 1  to the front end of the working cylinder AZ 1 . The control cylinder SZ 1  is provided with an annular groove  16  from which a control line  17  extends to the rear end of the working cylinder AZ 1 . The annular groove  16  is alternately communicated with the high pressure via radial bores  18  in the control piston SK 1  and with the return passage RL via a control groove  19  on the outer surface of the working piston SK 1 . The control groove  19  is constantly within the area of an annular groove  20  of the control cylinder SZ 1  connected with the return passage RL. A return line  21  extends from the working cylinder AZ 1  to the annular groove  20 . 
     Further, a control line  22  extends from the working cylinder AZ 1  to the control cylinder SZ 1 . The control line  22  is connected to the high pressure line  15  when the working piston AK 1  is in the retracted position (illustrated in FIG.  1 ), and it is connected with the return line  21 , when the working piston AK 1  is in the forward end position striking the anvil surface  12 . This switching of the control piston by the working piston is effected by a collar B 1  of the working piston. Another collar B 2  of the working piston defines the rear cylinder space into which the control line  17  leads, 
     The drive of the working piston AK 1  in a forward working stroke is effected by high pressure acting on the control surface SF 1  via the control line  17 . The control surface SF 2  opposite the control surface SF 1  is smaller than the control surface SF 1 . The control surface SF 2  is constantly subjected to high pressure. During the return stroke, the control surface SF 1  is not pressurized so that the working piston AK 1  is moved backward. In the working stroke, the force exerted on the larger control surface SF 1  outweighs the counter force exerted on the smaller control surface SF 2 . 
     The control line  22  controls the movement of the control piston SK 1  by exerting its pressure on the control surface SF 3 . The control piston SK 1  is hydraulically biased to the left, that is into the position corresponding to the return stroke of the working piston AK 1 . If, however, high pressure acts on the control surface SF 3  via the control line  22 , the control piston SK 1  is shifted to the represented (right-hand) position, in which it causes the working or impact stroke of the working piston AK 1 . 
     The device described above is known. According to the present invention, an additional second working piston AK 2  is provided that is hollow or tubular and strikes the annular anvil surface  13 . The outer surface of the working piston AK 2  is basically of the same design as that of the working piston AK 1 . It comprises two opposite control surfaces SF 3  and SF 4 , the control surface SF 4  being constantly exposed to high pressure, whereas the pressure acting on the control surface SF 3  is changed by the control piston SK 2 . The control piston SK 2  controls the working piston AK 2  via the control line  17   a  and the working piston AK 2  controls the control piston SK 2  via the control line  22   a . The control piston SK 2  is designed the same as the control piston SKi. It is also connected to the high pressure line HD and the return line RL. 
     The masses of both control pistons AK 1  and AK 2  are approximately equal. The mass of each piston is between 8 and 30 kg. The piston stroke of the working pistons is about 35 mm and the working rate of the working pistons is up to 3,500 impacts per minute. 
     In the embodiment of FIG. 1, each working piston has its own control piston. The movements of the working pistons are therefore not synchronized. Since it is not likely that both working pistons are operated with exactly the same rate, irregular impact sequences are obtained. 
     The two high pressure lines HD in FIG. 1 may either be connected to the same high pressure source or to different high pressure sources. Thus, it is possible to operate both working pistons and the associated control pistons with different pressure values. The different pressure sources can also be designed for different amounts of oil. 
     In the embodiment of FIG. 2, the working piston AK 1  and the working cylinder AZ 1  are designed in the same manner as in the first embodiment. The working piston AK 1  strikes the anvil surface  12  of the anvil  10 . The working piston AK 2  and the working cylinder AZ 2  are also designed as in the first embodiment. The working piston AK 2  is an annular piston striking the annular anvil surface  13 . In this embodiment, no separate control piston is provided, since the working piston AK 2  forms the control piston of the working piston AKi, and vice versa. The control line  17  of the first working cylinder AZ 1  is connected with the control line  22   a  of the first working cylinder AZ 1  and the control line  22  of the first working cylinder AZ 1  is connected with the control line  17   a  of the second working cylinder AZ 2 . The working pistons control each other and in opposite phase. This means that the working piston AK 2  takes its front position when the working piston AK 1  assumes its rear end position, and that the working piston AK 2  assumes its rear end position, when the working piston AK 1  takes its front end position. The movements of both working pistons are synchronized and phase-shifted by 180°. Thus, with a regular impact cycle, an impact rate is obtained that is twice the impact rate of each single working piston. 
     In the embodiment of FIG. 3, the working piston AK 1  is designed in the same manner as in the other embodiments, but with an additional control groove  30  provided which, depending on the position of the working piston, is either communicated with a pressure line  31  or with a return line  32 . By switching or exchanging the lines  31 ,  32 , the phase position of the working piston AK 2  can be reversed with respect to the working piston AK 1 . On the other hand, interrupting or blocking the pressure line  31  allows to deactivate the working piston AK 2 . It is also possible to connect the line  31  to a separate (different) high pressure source. In this manner, the working piston AK 2  can be operated with another pressure source, as is true for the working piston AK 1  and the control piston SK 1 . It is also possible that the other pressure source supplies a different amount of oil per unit time. The possibility to operate the working pistons with separate pressure sources increases the versatility of the percussion device. From the area of the control groove  30  a control line  17   a  leads out of the working cylinder AZ 1 . This control line extends into the working cylinder AZ 2  to pressurize or to de-pressurize the control surface SF 3  of the working piston AK 2 . In this embodiment, the working piston AK 1 , together with the control piston SK 1 , again forms a feedback circuit determining the rate, whereas the working piston AK 2  is controlled as a slave by the working piston AK 1 . 
     In the embodiment of FIG. 4, a control sleeve SK controls the first working piston AK 1  in the same manner as in the embodiment of FIG.  1 . The control piston SK is designed the same as the control piston SK 1 , but is provided with an extension  24 . The extension  24  comprises a control groove  25  that can bridge two annular grooves  26 ,  27  of the control cylinder SZ. The annular groove  26  is constantly connected with the return line RL and the annular groove  27  is connected with a control line  17   b , which is in turn connected with the control line  17   a  leading into the working cylinder AZ 2 . The control line  17   b  is alternately pressurized through radial bores  28  in the control piston SK and de-pressurized through the control groove  25 . The pressure in the control line  17   b  is in opposite phase to the pressure in the control line  17 , whereby both working pistons AK 1  and AK 2  are operated in opposite phases. The working piston AK 1  cooperates with the control piston SK to generate an oscillating movement, whereas the operating piston AK 2  is merely controlled as a slave but has no influence on the control. 
     As an alternative to the embodiment described in FIG. 3, it is also possible to operate the working piston AK 2  in phase with the working piston AK 1 . To this end, the control line  17   b  must be blocked and the control line  17  must be connected with the control line  17   a . In a synchronous operation with the same phase, the percussion rate is relatively low, but the single impact energy is all the higher. 
     It is also possible to switch between both modes, for example, to break rock with low-rate impacts of high single impact energy, and to work with a high percussion rate and low single impact energy in normal ground. 
     The embodiment of FIG. 5 largely corresponds to that of FIG. 4 so that the following description is restricted to the explanation of the differences. 
     According to FIG. 5, the control lines  17 ,  17   a  and  17   b  are connected to a switching element  34  which is a directional control valve. The switching element has three ports A, B, C, where C is an outlet that can selectively be connected to the inlet A or the inlet B, or be de-pressurized. 
     In FIG. 5, the switching element  34  is in the position in which it connects the inlet B with the outlet C. The inlet A is blocked. This means that the control pressure in the control line  17  controls both the working piston AK 1  and the working piston AK 2 , this control being synchronous. Both working pistons thus strike the shaft  14  together and at the same time. 
     When the switching element  34  is in the position illustrated in FIG. 6, it connects the inlet A with the outlet C. The inlet B is blocked. Since the control lines  17 ,  17   b  have inverse pressures, the two working pistons AK 1  and AK 2  are operated in opposite phases. The percussion rate is thus twice that of a single working piston. 
     In the position of the switching element  34  illustrated in FIG. 7, the inlets A and B of the switching element are blocked, while the outlet C is connected to the return line. Thus, the control line  17   a  is de-pressurized and the working piston AK 2  is deactivated. Only the working piston AK 1  is operative due to the control through the control line  17 . 
     As illustrated in FIG. 5, the pressure lines  15  that lead into both working cylinders AZ 1  and AZ 2  are each connected to an own gas pressure storage means  36  an  37 , respectively, so that the working pistons do not take each others pressure. Moreover, the return line RL is connected to a gas pressure storage means  38 .