DRILLING MACHINE

FIELD OF THE INVENTION The invention concerns a damping device for a percussion device according to the preamble of claim 1. The invention also concerns a percussion device and a drilling machine.

BACKGROUND OF THE INVENTION The aim of a damping device in a drilling machine is to protect the drilling machine from reflecting shock waves that occur during drilling. Further, the damping device aims to provide enhanced conditions for transfer of the feed force over the drill steel to the rock, in order to ensure rock contact during drilling.

From US 4 993 504 is previously know a damping device for percussive machines including a first chamber being connected to an accumulator and a second chamber for damping reflexes from the drill steel. A damping piston is with snug fit receivable into the second chamber, which results in that the reflexes of the rock are damped by liquid being pressed out through the slot being formed between the piston and the machine housing when the piston moves in a direction opposite to the striking direction. A non return valve is arranged between the chambers and is directed such that a liquid flow is allowed from the first chamber to the second chamber when the piston moves out from the second chamber.

There are also known so called floating dampers which are supplied with a constant flow and wherein the damping piston before a strike is intended to be positioned in a so called floating position, around which it can move in the striking direction as well as in the opposite direction. A damping chamber, wherein a damping piston is received, is connected to an accumulator, and a previously known representative -.of this category of dampers acts as a hydraulic spring, wherein, in practice, no energy reception or energy consumption exists for achieving real damping of the reflexes emanating from drilling, which results in the formation of an unwanted oscillating system.

It is an aim of the present invention to provide a further development of said damping devices which all in all results in enhanced working conditions for the percussion device and thereby more effective drilling.

MOST IMPORTANT FEATURES OF THE INVENTION

These aims are achieved in respect of an invention as mentioned initially through the features of the characterizing portion of claim 1.

Hereby is achieved, on the one hand an energy absorbing function, the other hand reduced risk of cavitation damages to the included components during operation of the device. In relation to the damping device in US 4 993 504, the problems are avoided with periodically very high pressure in the damping chamber itself - the second chamber - alternating with very low pressures in this chamber, which in the device according to the US document can result in cavitation damages to sealing' s and guides and also to the non return valve between the chambers.

In comparison with a conventional so called single damper, functional energy reception and thereby effective damping of reflected shock waves is achieved through the invention. Better conditions for rock contact during as great part as possible of the drilling cycle can be obtained as well as enhanced tightening of drill string joints and thereby better drilling economy. Longer service intervals and a longer working life of the involved details can also be expected. When the percussion device has driven forward the adapter or the corresponding component through a strike, a pressure reduction will occur in the damping chamber, which results in that the non return valve will open and the accumulator can fill up the damping chamber with pressurized liquid, which results in that the piston can quickly move towards the rock again and thereby ensure rock contact at the same time as the risk for cavitation damages be reduced.

In a preferred embodiment of the invention, the supply conduit for pressure liquid is connected to the accumulator and thereby the supply conduit is connected to the damping chamber over said non return valve. This result in that refilling of the accumulator is more effective and also that the components being connected to the supply conduit are protected from harmful pressure pulses emanating from the damping chamber .

By a control slot being arranged to be formed between the damping piston and a ring surface being position outward thereof, damping is achieved in correspondence to what is described above. By further, the ring surface being provided with at least one float hole for establishing a floating position of the damping piston, it is achieved that the damping piston will act so as to move a strike receiving component, such a drill steel adapter, to a striking position being advantageous for the percussion device, whereby low variation of the percussion energy of the percussion device will be the result.

When a choking channel with a second choking device is arranged to connect the damping chamber to the accumulator in parallel with the non return valve, there are achieved several advantages . Liquid being included in the damping system can be supplied to the damping chamber very fast through the choking device, already before the non return valve has been able to open. This brings about the advantage that excessive pressure reduction, which otherwise could occur inside the damping chamber can be avoided early during a percussion cycle.

Further, a equalizing re-flow of the liquid from the damping chamber to the accumulator is allowed. All in all the combination of non return valve and choking device arranged in parallel, will create a faster system with increased possibility of rock contact during a greater part of the cycle and further reduction of harmful pressure pulses in the associated components.

It is preferred that the return choking device and/or the second choking device are adjustable for the adaption of the damping device to prevailing requirements of the percussion device. The adjustability can be achieved through means that are per se known to the person skilled in the art. In principle, the smaller the area for energy reception that a choking device exhibits, the greater hardness the damper will have .

Corresponding advantages as above in respect of the damping device are achieved the respect of a percussion device and a rock drilling machine according to the invention.

Further features and advantages of the invention will be explained in the following detail description with reference to the annexed drawings .

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described in greater detail by way of embodiments with reference to the drawings, wherein: Fig. Ia diagrammatically shows an axial section of a damping device according to the invention in a percussion device of a drilling machine,

Figs. Ib and Ic show a detail of damping device in Fig. Ia with the damping piston in different positions, Fig. 2 diagrammaticalIy shows second embodiment of a damping device according to the invention, and

Fig. 3 diagrammatically shows a third embodiment of a damping device according to the invention.

DESCRIPTION OF EMBODIMENTS

In Fig. Ia is thus shown a damping device in connection with a percussion device, wherein a percussive piston 2 is arranged to act in a striking direction R (to the left in Fig. Ia) on a drill steal adapter 1. As is usual, a damping piston 8 being arranged surrounding a percussive piston 2 acts axially against the drill steal adapter 1 over a drill bushing 3. During strikes of the percussive piston against the drill steal adapter 1, in certain operational cases, i.a. depending on the properties of the rock, shock wave reflexes will tend to drive the drill steal adapter 1 in a direction opposite to the striking direction R, said shock wave reflexes being transmitted over the drill bushing 3 to the damping piston 8. The damping piston 8 has a piston portion 6, which is received in a ring-shaped damping chamber 7, which in turn is positioned radially outside an extended portion 8' of the damping piston 8. A flow q of pressure liquid is continuously supplied to the damping chamber 7 from a (not shown) pump through the supply conduit 14. To the supply conduit is connected an accumulator 13, which can be of a conventional kind, and which has been loaded with a suitable counter-pressure of a gas volume on one side of a flexible membrane, on the other side of which pressure liquid can be supplied/discharged. The supply conduit 14 is connected to the damping chamber 7 over a system including a choking device (second choking device) 11, which is connected in parallel to a non return valve 12, which is directed so as to allow a liquid flow to the damping chamber 7 but to prevent flows in direction from the damping chamber 7.

From the damping chamber 7 leads a return channel, which includes: at least one float hole 10 (suitably two float holes being positioned diametrically to each other and possibly even more float holes) , for ensuring that the damping piston 8 will occupy a desired floating position, a return chamber 9 and a conduit emanating from the return chamber 9, which finally debouches in a tank 5. This conduit can possibly include a return choking device 4, which is the case in the embodiments in Figs . Ia and 2. The tank 5 can be connected to said pump (not shown) for pressure liquid. A certain reflow of liquid to the damping chamber, and thereby reduction of pressure variations there inside, can also to certain extent be obtained through the arrangement of float holes 10, second choking device 16 in the form of a control slot and return chamber 9 when the pressure in the damping chamber momentary is reduced because of a received reflex from the rock.

In Fig. Ib a damping piston 8 is shown where it has essentially occupied said floating position, wherein a control edge 6', radially most outwardly on the piston portion 6, in co-operation with a mouth of one (or more) float hole forms a variable float hole choking device 20 in dependence of the axial position of the damping piston. During normal operation of a percussion device according to the invention, and when the rock reflexes are moderate, the damping piston will move with small axial movements approximately around the position shown in Fig. Ib (the floating position) .

From Fig. Ic is apparent that the damping piston 8 through the reception of a somewhat greater shock wave reflex from the drill steel adapter 1 has moved a distance opposite to the striking direction R and thus moved longer inside the damping chamber 7. Through this movement there has been established a choking slot 16 between a circular cylindrical outwardly turned surface 17 of the damping piston 8 and a circular cylindrical inwardly turned ring surface 8 of a component being included in a machine housing of the percussion device.

This control slot 16 is here indicated as a first choking device in a first choking channel of the damping device. During a movement of the damping piston 8 opposite to the striking direction hereby a pressure increase will occur in the damping chamber 7. No liquid will pass through the non return valve, since this non return valve only allow a flow in the direction to the damping chamber. Because of the pressure increase, however, liquid will be pressed on the one hand through the first choking device being comprised of the choking slot 16, on the other hand through the second choking device being comprised of the choking device 11.

Hereby energy will be consumed in said choking devices 11, 16 and 20 respectively, and contribute to effective damping of the reflected shock wave. As it occurs, energy will be received also in the return choking device 4.

Through the continuous supply/through- flow of pressure liquid, as is described above, it will be ensured that heat developed in these choking devices will be cooled off. It should be observed that the control slot is exaggerated in Fig. Ib and Ic for clarity reasons. 21 indicates a sealing acting against the damping piston 8, which ensures that return flow from the damping chamber 7 (essentially) only flows through said float holes 10.

The embodiment in Fig. 2 differs from the one in Fig. Ia only through the absence of the second choking device. In this embodiment, all energy reception is thus in the first choking device 16, as explained above, and which is established during a movement to the right, opposite to the striking direction R of the damping piston 8 from the positioned shown in Fig. 2.

The embodiment in Fig. 3 differs from the one in Fig. Ia in that the supply conduit for pressure liquid 14 directly adjoins to the damping chamber 7. In this case, all recharging of the accumulator thus is over the second choking device 11. In this case it can also exist that a certain pressure fluctuation in the damping chamber 7 can be transferred into the supply conduit 14. The invention can be modified within the scope of the following claims, and as an example the percussion device can be constructed otherwise and even without a conventional percussive piston. In that case it can be a so called impulse machine . Transfer of shock wave reflexes to the damping piston can also be arranged otherwise. The components in the machine housing can be arranged otherwise and, for example, the ring- shaped component outside the most extended portion of the damping piston can be an integrated part of the machine housing itself.

The liquids that are used with the invention are the usual hydraulic liquids for similar applications.