MACHINE FIELD OF THE INVENTION

The invention relates to a damping device for a

percussion device of a rock drilling machine including a damping piston being received in a damping chamber whereto is connected a damping flow circuit including a supply conduit, and wherein an outlet conduit is also connected to the damping chamber. The invention also concerns a method of damping, a percussion device and a rock drilling machine.

BACKGROUND OF THE INVENTION

The purpose of a damping device for a percussion device of a rock drilling machine is essentially to protect the rock drilling machine and the drill steel from harmful reflective shock waves that occur during drilling. The damping device also aims to provide enhanced properties for transferring the feed force of the drill steel to the rock by ensuring rock contact during drilling.

From US 4,993,504 is previously known a damping device for percussion machines including a first chamber which is connected to an accumulator and a second chamber for damping reflexes emanating from a drill steel. A damping piston is with tight fit introduced into the second chamber, resulting in that reflexes from the rock are cushioned by liquid being pressed out through the slot formed between the piston and the machine houses when the piston moves in a direction opposite to the striking direction. The one way valve can normally be arranged between the chambers and be 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. So called floating dampers are also previously known, wherein the damping piston before an impact is intended to be located in a so called floating position, around which it can be displaced in the striking direction as well as opposite thereto. A damping chamber wherein a damping piston is

arranged is connected to an accumulator and a previously known representative of this category of dampers functions as a hydraulic spring wherein in practice no reception or

consumption of energy worth mentioning exists for achieving a true damping of the reflexes emanating from the drilling resulting in an unwanted oscillating system.

It is an aim of the present invention to provide a further development of the mentioned damping devices which generally seen leads to conditions for greater flexibility of the percussion device and thereby more effective drilling.

MOST IMPORTANT FEATURES OF THE INVENTION

These aims are obtained in respect of an invention as described initially through a damping flow regulator being controllable in respect of damping flow in the damping flow circuit being arranged in said supply conduit, and a control means being arranged to emit control signals to the damping flow regulator for regulating said damping flow. Hereby the properties of the damper can be amended effectively and be adjusted to prevailing conditions during for example different drilling phases.

The most important effect according to the invention and the aspect that will probably have most importance in respect of normal drilling is, however, that, through the invention, it is achieved that the anticipated damping flow is really obtained during normal drilling.

If for example a damping flow of 8 1/min is the intended standard flow for the machine in question, it is ensured, through the invention, that this flow is indeed obtained as a damping flow, which is in contrast to machines according to the background art, wherein indeed a certain damping pressure may be achieved but the damping flow will vary greatly, resulting in that the machine will not fully reach its

potential during different situations.

As a further example it results in saving energy, not being negligible, to be able to reduce the damping flow during drilling phases with low effect as in during the collaring phase and during drilling in loose rock. Hereby that advantage is obtained that the need of overcoming a normally relatively important idling damping pressure, during pressing-in of the damping piston to the floating position in order to be able to start drilling, is avoided. As an example it could be

mentioned that up to 1/3 of the feed force could be required to overcome said pressure during normal full drilling.

It is also very essential to be able to entirely turn off the damping flow in all situations when there is no active drilling .

The invention also gives a possibility of increasing the damping flow above a normal value for "normal drilling" in situations requiring a higher effect, which for example could be during drilling upwardly, when the entire weight of the drill string influences the damping. A further case when increased damping flow is of interest and desirable is during start of the drilling machine, wherein a higher damping flow contributes to effective and fasts warming of the drilling machine which thereby can be put in operation faster and with more protectable properties from the beginning. Also during scaling using the drilling machine, a high damping flow is normally desirable.

Furthermore, through the invention, the damping function will be more independent of viscosity changes in the liquid and other operational conditions for the damping that can be changed during the drilling process.

Providing a control means to emit control signals to the damping flow regulator for desired damping flow in the damping flow circuit minimizes the risk of an operator making mistakes that could influence the drilling negatively, and the system including the damping device can be made to adapt accurately to the operational conditions in different drilling phases.

These advantages are accentuated when a sensor is arranged for sensing a parameter which is related to the damping flow, and when the control means is arranged to receive signals from said sensor for emitting said control signals for measuring and regulating during the drilling process. In particularly it is preferred that the control means is arranged to control the damping flow regulator to maintain a constant or essentially constant damping flow as seen over a drilling phase.

Suitably the sensor is a pressure sensor arranged to sense the pressure in the supply conduit downstream of the damping flow regulator, wherein the damping flow is set based on sense pressure. It is also possible to detect the damping flow itself in the inlet flow conduit for regulation. It is not excluded that also other parameters can be subject to sensing .

Preferably the control means is manually settable for adjustment of set damping to operation in at least one of the following: collaring mode, scaling mode, high effect mode (drilling upwards; heating mode), low effect mode and normal drilling .

Hereby is arranged that damping flow parameters are set in accordance with the conditions prevailing for the specific situation of the respective drilling or application phase. Typically an altered damping flow effects the floating position since a greater flow requires that the outlet

channel/the float hole is more open, wherein the damping piston presumes a position "more forward" in the machine housing and vice versa. Altered position in turn influences the damping since the position of the damping piston effects the throttle slot length.

Changed flow is typically related to required feed force and the position of the damper in different situations. A greater flow also gives a little quicker reaction and quicker pressure build up in the damper in a drilling sequence where the drill bit hits the rock after having made an idle impact without rock contact .

Suitably the damping flow regulator is a pressure compensated proportional flow regulating valve.

Suitably an accumulator is connected to the damping chamber for pressure levelling purposes.

It is preferred that an outlet throttling for throttling of pressure fluid exiting the damping chamber is arranged in the outlet conduit. Most preferred the outlet throttle is adjustable possibly controlled by said control means.

In operation, in the region where the outlet conduit opens in the damping chamber, a throttle slot will be

established between the damping piston and a cylindrical ring- shaped surface being located radially outside. The outlet conduit hereby opens into the damping chamber while forming at least one float hole for establishing a floating position of the damping piston, wherein a float hole throttle is arranged to be established between a control edge radially most

outwards on a piston portion of the damping piston and said at least one float hole.

In a preferred aspect of the invention, the damping piston also includes a second piston portion for co-operation with a second ring-shaped damping chamber. Hereby the damping function is essentially enhanced and provided the properties of a double damper.

The invention also relates to a percussion device, a rock drilling machine and a method including corresponding features and advantages as are mentioned above.

In the inventive method: The damping flow is regulated by a damping flow regulator being arranged in said supply

conduit, and control signals are emitted by a control means to the damping flow regulator for regulating said damping flow.

Preferably a parameter which is related to the damping flow is sensed by a sensor, wherein the control means receives signals from said sensor for emitting said control signals.

Suitably the damping flow regulator is controlled to maintain a constant or essentially constant damping flow as seen over a drilling phase.

Preferably the sensor senses the pressure in the supply conduit downstream of the damping flow regulator.

It is preferred that the control means is set for adjustment of set damping to operation in at least one of the following: collaring mode, scaling mode, high effect mode

(drilling upwards; heating mode) , low effect mode and normal drilling .

Suitably pressure fluid exiting the damping chamber is throttled by an outlet throttling in the outlet conduit. To a certain extent, this is made to facilitate measuring the damping pressure. Accurate control of the damping flow

regulator according to the invention gives the possibility of a reduced degree of throttling while maintaining an adequately ensured damping flow.

Further features and advantages of the invention will be explained in the following detailed description given 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:

Figs. 1 and 2 show a drilling machine according to the invention in a perspective view and in an axial section respectively,

Fig. 3 shows, diagrammatically in a part section, a damping device according to the invention, and

Fig. 4 diagrammatically shows a block diagram for illustrating a method according to the invention.

DESCRIPTION OF EMBODIMENTS

Figs. 1 and 2 show a rock drilling machine 1 according to the invention in a perspective view and in an axial section respectively, wherein 2 indicates a housing of the rock drilling machine and 3 a shank adapter for the connection to drill steel for forming a drill string.

As usual, the rock drilling machine 1 exhibits a

percussive piston 4 for intermittent striking action on the shank adapter 3. Against the shank adapter 3 further is applied a drill sleeve 5, which in a per se known manner is pressed in the striking direction with the aid of a damping piston 8. The purpose of the damper is i.a. to receive and damp reflecting shock waves that occur during drilling.

Resulting from the strikes of the percussive piston, in certain operational cases, there will occur, depending i.a. on the properties of the rock, shock wave reflections that will tend to drive the shank adapter in a direction opposite to the striking direction R, said shock wave reflections being transmitted over the drill bushing to the damping piston.

The rock drilling machine 1 is, except for the damping device, of a conventional kind and the further parts thereof will therefore not be described in greater detail here. In Fig. 3 is shown more diagrammatically the function of the damping device according to the invention. The percussive piston 4 operates in a striking direction against the shank adapter 3 and is in the region of an impact end surrounded by said drill sleeve 5 which is axially moveable in a cylindrical space in the housing 2. The drill sleeve 5 is thus arranged to be pressed against the shank adapter 3 by the damping piston 8 which is likewise received in a cylindrical space inside the housing 2. Hereby is formed a first ring-shaped damping chamber 7 which is arranged to co-operate with the first piston portion 6. 17 indicates a second ring-shaped damping chamber which co-operates with a second piston portion 20.

The damping piston 8 further exhibits an extended piston portion 8', which for guiding purposes co-operates with a corresponding cylindrical portion of the housing 2.

A damping flow source in the form of a pump 9 (in this embodiment; other variants can exist) is connected to the first ring-shaped damping chamber 7 over a supply conduit 14 for damping flow, whereby in said supply conduit 4 there is arranged a damping flow regulator 10. The purpose thereof is to ensure that a desired damping flow is obtained in the damping flow circuit, which includes the supply conduit 14, said first and second ring-shaped damping chambers and a outlet conduit 15.

In the supply conduit 14 there is further arranged a pressure sensor 12 for sensing the damping flow pressure and an adjustable control means 11, which in the shown embodiment is manually adjustable as well as adjustable on the bases of signals emitted by the pressure sensor 12 for setting the damping flow regulator 10. The damping flow regulator is hereby preferably manually settable as well as controllable by the control means 11, which in turn can be manually actuated and be controllable by way of a control unit, which as an example can be integrated in the control system (CPU on Fig. 3) of the drilling machine. It is however not excluded that the damping flow regulated 10 in its most simple form is exclusively manually settable for obtaining a nearly constant damping flow for a certain drilling operation.

21 indicates an auxiliary channel for damping flow, said auxiliary channel aiming to supply a damping flow to the second ring-shaped damping chamber 7. On Fig. 3, this

auxiliary channel 21 is shown emanating from the first ring- shaped damping chamber over a one way valve to and opening into the second ring-shaped damping chamber 17. The one way valve, which can be formed in different per se known manners prevents return flow from the second ring-shaped damping chamber to the first ring-shaped damping chamber.

In operation of the percussion device with a damping device according to Fig. 3, reflexes in the drill string will be transmitted as movements of the shank adapter 3 axially against the striking directions R. These movements are transferred over the drill sleeve 5 to the damping piston 8 which likewise is subjected to an axial movement opposite to the striking directions R. Hereby the first piston portion 6 will move in this direction opposite to the striking direction R inside the first damping chamber 7 against action of a counter force being provided by the liquid being present in this first ring-shape damping chamber 7.

During this movement, a control edge 6' of the first piston portion 6 will cover at least one float hole 22 being an outlet opening (openings) in the damping chamber. Preferably two float holes are arranged placed diametrically to each other or possibly a plurality of float holes being distributed over the perimeter.

If the damping piston 8 through the reception of a somewhat greater shock wave reflex has been displaced a distance opposite to the striking directions R and thus has entered further into the damping chamber 7, a throttle slot 24 will be established through this displacement being formed between the control edge 6' outermost on the first piston portion 6 and a cylindrical outer wall 18 of the first ring- shaped chamber 7. The liquid at the moment being present in the first ring-shape damping chamber 7 will partly be forced to be pressed into an accumulator 25, which is arranged to level the pressure in the supply conduit. Further, a remaining part of this liquid will pass through the throttle slot 24 whereby the certain part of the reflected energy will be received as heat in the liquid in the throttle and thereby contribute to damping of the reflected shock wave. At

occasions, energy can also be received in a return or outlet throttle 16 being arranged in the outlet conduit 15.

Further, said second piston portion 20 of the embodiment in Fig. 3 will act against the liquid being present in the second ring-shaped damping chamber 17, whereby said liquid will pass a slot 23 being formed between a control edge outermost on the second piston portion 20 and the cylindrical outer wall of the second ring-shaped damping chamber 17.

Hereby a part of the reflected energy will be absorbed by the liquid streaming out being heated during passage through the slot 23.

In principle, the damping device of Fig. 3 functions as double damper, wherein the greatest part of the damping work is performed in the slot 23 whereas the throttle slot in the region of the float hole (holes) 22 to a great extent

functions so as to provide a defined floating position and thereby a defined striking position for the percussion device.

19 indicates a tank for the reception of a return flow through the outlet conduit 15. During normal operation of a percussion device according to the invention, and when rock reflections are moderate, the damping piston will move with small axial movements

approximately around the position shown in Fig. 3 (floating position) .

Because of the through-flow of liquid, it will be ensured that heat developed in the throttling will be cooled away.

In the block diagram according to Fig. 4, which concerns an example only of the invention is indicated:

Position 26 the start of the sequence.

Position 27 supply of a damping flow to a damping chamber.

Position 28 regulating the damping flow in order to obtain a desired set damping flow in the damping flow circuit.

Position 29 that the damping flow regulator is controlled by a control means for holding a constant or essentially constant damping flow as seen over a drilling phase.

Position 30 that the damping flow is regulated such that set damping is adjusted to operation in at least one of the following: collaring mode, scaling mode, high effect mode (drilling upwards; heating mode) , low effect mode and normal drilling .

Position 31 the end of the sequence.

The invention can be modified within the scope of the following claims and the percussion device can for example be constructed otherwise and even without a conventional impact piston. In that case it can be a so called impulse machine.

The damping device is shown on Fig. 3 in the form of a double damper but it should be understood from the above that the invention is not limited to this embodiment and that it is also applicable in other kinds of dampers such as for example for a single damper, wherein the second ring-shaped damping chamber and the piston portion co-operating therewith as seen in that Figure is eliminated. The supply conduit can be provided with a throttling.

The invention is applicable also in percussion devices with several damping pistons operating in separate damping chambers . Such an arrangement can be constructed such that the damping pistons are arranged radially outside each other concentrically with the cylinder of the percussion device. In another variant, a plurality of suitably circular cylindrical damping pistons each operate in one damping chamber and being arranged distributed around the cylinder of the percussion device. Damping flow is advantageously transmitted to the different damping chambers through a suitable arrangement for flow distribution.

The invention is also applicable in respect of damping devices that do not include any accumulator in the damping flow circuit.

The arrangement for transmitting shock wave reflexes to the damping piston can also be arranged differently. The components in the machine housing can be arranged otherwise and, for example, the ring-shaped component outside of the most extended part of the damping piston can be an integral part of the machine housing itself.

The liquids that are used in connection with the invention are the usual hydraulic liquids for similar

applications.