TECHNICAL FIELD

The present disclosure relates to a damping arrangement for a hydraulic rock drilling machine, and to a hydraulic rock drilling machine comprising such a damping arrangement.

BACKGROUND

Rock drilling machines, drill hammers, and other impact mechanisms operate with repetitive impact in a striking direction of the machines. To protect the machines from reflected shockwaves occurring in response to such repetitive impacts, the machines include damping arrangements. The damping arrangements may also improve rock contact during drilling, thereby improving transfer of the feed force from the rock drilling machine over the drill bit to the rock.

Damping arrangements for rock drilling machines typically include an axial damping sleeve extending coaxially with a percussion piston of the machine. The damping sleeve is located within a housing and is movable back and forth with respect to both the housing and the percussion piston. With respect to the housing, the damping sleeve is movable around a floating position in which it is intended to be positioned prior to a strike. A hydraulic arrangement is generally provided for maintaining the floating position, i.e. , for returning the damping sleeve to the floating position after each strike. A pressurized damping cavity formed between the damping sleeve and the housing is used for absorbing the reflected shockwaves occurring in response to each strike. As such a shockwave reflected by the rock acts on the damping sleeve and presses it rearward with respect to the striking direction, hydraulic fluid is forced out from the damping cavity via a narrow slot. A cushioning effect is thereby obtained. The damping sleeve thereafter reassumes the floating position. A constant flow of hydraulic fluid to the damping arrangement is typically necessary for maintaining the floating position during drilling. This requires a tuning of the flow, which may be time consuming, and which may sometimes result in difficulties to maintain the floating position if the drilling conditions change during the drilling operation. The constant flow requirement may further necessitate the use of a dedicated hose for supplying hydraulic fluid to the damping arrangement.

EP3260647 discloses a damping arrangement for a hydraulic rock drilling machine in which two cavities located between the damping sleeve and the housing are fluidly connectable by a conduit depending on a position of the damping sleeve with respect to the housing, one of the cavities being connected to a pressure accumulator. During drilling, the pressure within one of the cavities varies in dependance on the position of the damping sleeve and acts to return the damping sleeve to a floating position.

It would be beneficial to provide a damping arrangement for a rock drilling machine with an improved ability to reach and maintain a floating position of the damping sleeve.

SUMMARY

A primary object of the present disclosure is to achieve an in at least some aspect improved damping arrangement for a hydraulic rock drilling machine and an in at least some aspect improved hydraulic rock drilling machine. In particular, it is an object to provide a damping arrangement and a hydraulic rock drilling machine with an improved ability to reach and maintain a floating position of the damping sleeve. Another object is to achieve a hydraulic rock drilling machine which has a less complex hydraulic arrangement.

At least the primary object is achieved by a damping arrangement according to claim 1. Thus, a damping arrangement for a hydraulic rock drilling machine provided with a percussion piston configured for generating impact pulses in a forward axial direction along a longitudinal axis of the rock drilling machine is provided. The damping arrangement comprises a housing defining an annular space extending along the longitudinal axis. It further comprises a damping sleeve extending along the longitudinal axis within the annular space of the housing, wherein the damping sleeve is slidably movable along the longitudinal axis within the housing, the damping sleeve thereby being movable around a floating position as defined with respect to the housing.

The damping arrangement further comprises first, second and third cavities formed between the housing and the damping sleeve and spaced apart with respect to one another along the longitudinal axis. The damping sleeve comprises a first pressure surface provided in the first cavity, and a second pressure surface provided in the second cavity, wherein the second cavity is arranged to be pressurized via the first cavity, and wherein the third cavity is arranged to be fluidly connected to a hydraulic fluid source.

The damping arrangement further comprises a fluid communication conduit arranged to open and fluidly connect the first cavity to the third cavity when the damping sleeve moves axially rearward from its floating position, and to be closed and fluidly disconnect the first cavity from the third cavity when the damping sleeve is in a forward position provided axially forward of its floating position. It also comprises a fluid return conduit arranged to open and release fluid from the first cavity when the damping sleeve moves axially forward from its floating position, and to be closed when the damping sleeve is in a rearward position provided axially rearward of its floating position. The forward and rearward movements and positions of the damping sleeve from the floating position are herein relative movements and positions, respectively, with respect to the housing.

By providing a fluid communication conduit and a fluid return conduit that are both configured to open and close depending on an axial position of the damping sleeve, a distinct floating position can be achieved and the ability of the damping arrangement to maintain the floating position of the damping sleeve can be improved in comparison with solutions comprising a single position dependent conduit. The damping sleeve is thus movable back and forth along the longitudinal axis, and the cooperating fluid communication and fluid return conduits ensure that it reassumes its floating position after each strike.

The pressure acting on the first pressure surface in the first cavity is dependent on the axial position of the damping sleeve with respect to the housing, and the first and second cavities will serve to return the damping sleeve to its floating position after a percussion strike. The second cavity will generally act to absorb the shockwaves generated during striking.

The first, second and third cavities may preferably be annular cavities extending around the damping sleeve, defined by internal and external grooves formed in the housing and in the damping sleeve, respectively.

The hydraulic fluid source may herein be a hydraulic fluid source providing a constant pressure, such as a constant pressure hydraulic fluid source used to pressurize the percussion piston. It is possible, but not necessary, to use a constant fluid flow source instead of a constant pressure source. In either case, the hydraulic fluid source provides hydraulic fluid that can be used to pressurize both the first and the second cavities provided between the damping sleeve and the housing.

The housing may be provided with an inner liner. Such a liner is herein considered as a part of the housing.

The fluid communication conduit is preferably configured to open gradually as the damping sleeve moves axially rearward from its floating position, and to close gradually as the damping sleeve returns to its floating position. Similarly, the fluid return conduit is preferably configured to open gradually when the damping sleeve moves axially forward from its floating position, and to close gradually when the damping sleeve returns. The opening/closing of the fluid return conduit and the closing/opening of the fluid communication conduit may start at slightly different axial positions of the damping sleeve. Thus, there may be an axial overlap during which both conduits are closed.

Optionally, the fluid communication conduit is formed in the housing. By forming the fluid communication conduit in the housing rather than in the damping sleeve, the fluid communication conduit is less prone to wear and is also easier to make.

Optionally, the first and second pressure surfaces face in a rearward axial direction opposite to the forward axial direction. In other words, the first and second pressure surfaces face away from a shank adapter and/or a drilling tool of the hydraulic rock drilling machine. This contributes to a relatively uncomplicated construction with an in the forward axial direction successively increasing diameter of the damping sleeve.

Optionally, the damping sleeve comprises a first external groove, a second external groove, and a third external groove, and the housing comprises a first internal groove, a second internal groove, and a third internal groove, wherein the first cavity is delimited by the first internal and external grooves, the second cavity is delimited by the second internal and external grooves, and the third cavity is delimited by the third internal and external grooves, wherein the fluid communication conduit at a first end thereof opens into the first internal groove, and at a second end thereof is positioned to open into the third external groove when the damping sleeve is in the rearward position. The grooves may be annular grooves as discussed above. Optionally, the second end of the fluid communication conduit is positioned axially rearward of the third internal groove. Hereby, it can open into the third external groove of the damping sleeve when the damping sleeve moves rearward and allow hydraulic fluid to flow between the third cavity and the first cavity. Furthermore, the opening takes place gradually as the damping sleeve moves rearward from the floating position, and the opening closes gradually as the damping sleeve moves forward again. The gradual opening and closing lead to a continuous adjustment of the pressure within the first cavity during movement of the damping sleeve.

Optionally, both of the fluid communication conduit and the fluid return conduit are closed when the damping sleeve is in its floating position. Thus, only as the damping sleeve moves out of the floating position, one of the fluid communication conduit and the fluid return conduit opens.

Optionally, the fluid return conduit is positioned to open into a first external groove of the damping sleeve when the damping sleeve is in the forward position, the first external groove delimiting the first cavity.

Optionally, the fluid return conduit is positioned axially forward of a first internal groove of the housing, the first internal groove delimiting the first cavity. In this way, it is ensured that the fluid return conduit only opens when the damping sleeve moves to a forward position in which the first external groove overlaps with the opening of the fluid return conduit. The location of the fluid return conduit axially forward of the first internal groove implies that the fluid return conduit is opened and closed gradually as the damping sleeve moves forward and rearward, respectively.

Optionally, the damping arrangement comprises a leakage slot between the first and second cavities, the leakage slot allowing fluid leakage between the first and the second cavities. The second cavity is herein arranged to be pressurized via the first cavity and the leakage slot. The direction of the leakage will depend on the relative pressures within the first and second cavities. By providing a relatively narrow leakage slot, the second cavity can provide an efficient damping during drilling. Instead of a leakage slot, a throttled conduit may be provided between the first and second cavities. Optionally, the leakage slot is formed between the damping sleeve and the housing, such as by a liner of the housing. In other words, it is delimited by the damping sleeve on one hand and by the housing on the other hand. This is a constructionally straightforward way of providing the leakage slot.

Optionally, the damping arrangement comprises a fluid supply conduit for fluidly connecting the third cavity to a hydraulic fluid source. The fluid supply conduit may preferably comprise means for throttling the supply of hydraulic fluid, such as a throttle or a narrow passage, for reducing the flow of hydraulic fluid to the damping arrangement and reduce power consumption. Preferably, means for throttling the flow is also provided in the fluid return conduit. Thus, a throttle upstream the third cavity and a throttle downstream the first cavity may be connected in series for throttling the flow of hydraulic fluid to and from the damping arrangement. By throttling the flow, an improved control of the damping is achieved.

Optionally, the second cavity is configured to provide a higher shock absorption response than the first cavity. The second cavity is thereby suitable for absorbing shockwaves generated during drilling, while the first cavity is responsible for maintaining the floating position of the damping sleeve. The higher shock absorption response may be achieved by proper dimensioning of the second cavity and of the leakage slot, or similar, connecting the second cavity to the first cavity via which the second cavity is pressurized.

Optionally, the damping sleeve has a first outer diameter d1 as measured axially forward of the first cavity, a second outer diameter d2 as measured between the first and second cavities, and a third outer diameter d3 as measured axially rearward of the second cavity, wherein d1 > d2 > d3. Hereby, the first pressure surface is provided in the transition between the first and second diameters, and the second pressure surface is provided in the transition between the second and third diameters.

According to a second aspect, at least the primary object is achieved by a hydraulic rock drilling machine according to claim 14. The hydraulic rock drilling machine comprises a percussion piston configured for generating impact pulses in an axial direction of the rock drilling machine, and a damping arrangement according to the first aspect, wherein the damping sleeve extends coaxially with the percussion piston, between the percussion piston and the housing. Optionally, the percussion piston and the fluid supply conduit of the damping arrangement are both fluidly connected to the same hydraulic fluid source. Thus, the same hydraulic pressure source can be used for percussion drilling, damping, and for maintaining the floating position of the damping sleeve. This reduces the amount of hoses needed, contributing to a less complicated hydraulic arrangement, and it may further reduce the power consumption of the damping arrangement since pressure losses in a separate damping hose may be avoided. A further advantage is that the risk of causing damage to the drilling machine by starting the percussion piston without activating the damping arrangement is eliminated, thanks to the simultaneous pressurization of the percussion piston and the damping arrangement. A separate hose for providing hydraulic fluid to the damping arrangement may be connected in case it is desired to pressurize the damping arrangement when the percussion piston is not in usage.

Optionally, the hydraulic rock drilling machine further comprises a shank adapter arranged to abut an impact generating surface of the percussion piston, the shank adapter being arranged to receive said impact pulses from the percussion piston. Instead of a separate shank adapter, a drilling tool comprising a shank adapter may be used.

Further advantages and advantageous features of the disclosure are disclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS (OPTIONAL)

With reference to the appended drawings, below follows a more detailed description of embodiments of the disclosure cited as examples.

In the drawings:

Fig. 1 illustrates a hydraulic rock drilling machine according to an embodiment,

Fig. 2 is a sectional view of a damping arrangement of the rock drilling machine illustrated in Fig. 1 ,

Fig. 3 schematically illustrates parts of a damping arrangement according to an embodiment in a first position, and Fig. 4 schematically illustrates the damping arrangement from Fig. 3 in a second position.

The drawings show diagrammatic, exemplifying embodiments of the present disclosure and are thus not necessarily drawn to scale. It shall be understood that the embodiments shown and described are exemplifying and that the disclosure is not limited to these embodiments. It shall also be noted that some details in the drawings may be exaggerated in order to better describe and illustrate the disclosure. Like reference characters refer to like elements throughout the description, unless expressed otherwise.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A hydraulic rock drilling machine 1 according to an embodiment of the present disclosure is shown in Fig. 1. The hydraulic rock drilling machine 1 , hereinafter also referred to as the drilling machine 1 , comprises a percussion piston 2 configured for generating impact pulses in a forward axial direction A of the drilling machine 1 , the forward axial direction A extending along a longitudinal axis of the drilling machine 1. A shank adapter 3 arranged to abut an impact generating surface of the percussion piston 2 is further provided, the shank adapter 3 being arranged to receive the impact pulses generated by the percussion piston 2. On the shank adapter 3, drilling equipment (not shown) may be mounted, herein by threaded engagement. The drilling equipment may include a tool in the form of a drill bit or similar acting on a rock surface ahead of the drilling machine 1 , and possibly one or more drill rods for force transfer between the shank adapter and the drill bit. Thus, the shank adapter 3 transfers the impact pulses generated by the percussion piston 2 to the drilling equipment.

The drilling machine 1 further comprises a damping arrangement 10 for damping rock reflexes occurring after a percussive strike of the percussion piston 2 against the shank adapter 3. The damping arrangement 10 also ensures a good contact between the drill bit and the rock surface, thereby contributing to increased drilling speed.

The damping arrangement 10 includes a housing 4, defining an annular space extending in the axial direction A. It further includes a damping sleeve 5 extending in the axial direction A within the annular space of the housing 4. The damping sleeve 5 extends coaxially with the percussion piston 2, between the percussion piston 2 and the housing 4. The damping sleeve 5 is slidable with respect to the percussion piston 2 as well as with respect to the housing 4. It is typically not in contact with the percussion piston 2. A bushing 6 is provided between the damping sleeve 5 and the shank adapter 3. Although not illustrated herein, the drilling machine 1 may have various configurations for force transfer between the percussion piston 2 and the shank adapter 3, as well as between the shank adapter 3 and the damping arrangement 10. For example, the bushing 6 may be omitted or differently designed.

A floating position of the damping sleeve 5 is defined with respect to the housing 4. Within the housing 4, the damping sleeve 5 is slidably movable in the forward axial direction A as well as in a rearward axial direction around the floating position. The rearward axial direction is opposite to the forward axial direction A.

Reference is now made to Fig. 2, showing the damping arrangement 10 from Fig. 1 in closer detail. Reference is also made to Figs. 3-4, schematically illustrating the damping arrangement 10 according to an embodiment of the disclosure, and a working principle thereof. The working principle of the damping arrangement 10 illustrated in Fig. 2 corresponds to the working principle described with reference to Figs. 3-4. The damping arrangement 10 is in Fig. 2 shown in the floating position. In the floating position, both the fluid communication conduit 16 and the fluid return conduit 17 are closed. Fig. 3 shows the damping sleeve 5 in a rearward position with respect to the floating position, and Fig. 4 shows the damping sleeve 5 in a forward position with respect to the floating position. Although the damping sleeve 5 and the housing 4 are annular and extend around the longitudinal axis as illustrated in Fig. 2, only upper portions of those parts are illustrated in Figs. 3-4.

The housing 4 is formed with first, second and third internal grooves 31 , 32, 33 formed in an inner annular surface of the housing 4. The damping sleeve 5 is further formed with first, second and third external grooves 41 , 42, 43 opposing the first, second and third internal grooves 31 , 32, 33, respectively. Each one of the external grooves 41 , 42, 43 at least partly overlaps a respective one of the internal grooves 31 , 32, 33 so as to define first, second, and third cavities 11 , 12, 13 provided between the housing 4 and the damping sleeve 5. The cavities 11 , 12, 13 are spaced apart along the longitudinal axis and may be annular cavities, extending around a circumference of the damping sleeve 5. Herein, the first cavity 11 is located foremost in the forward axial direction A, the third cavity 13 is located rearmost, and the second cavity 12 is located between the first and third cavities 11 , 13. The third cavity 13 is connected to a hydraulic fluid source (not shown) via a fluid supply conduit 15. The fluid supply conduit 15 herein comprises a throttle 18 via which pressurized hydraulic fluid is fed to the third cavity 13, such as at a constant pressure. The hydraulic fluid source thus provides hydraulic fluid to the damping arrangement 10 via the fluid supply conduit 15 and the third cavity 13. The hydraulic fluid source may comprise a pump fluidly connected to a hydraulic fluid supply, which pump is controlled to deliver hydraulic fluid at a constant pressure. A pressure accumulator (not shown) may also be provided at an inlet of the damping arrangement 10 to even out the inlet pressure. The hydraulic fluid source may advantageously be the same hydraulic fluid source as used for pressurizing the percussion piston 2.

A fluid communication conduit 16 is further provided in the housing 4. The fluid communication conduit 16 has a first end 16a opening into the first internal groove 31 , delimiting the first cavity 11 , and a second end 16b with an opening provided axially rearward of the third internal groove 33. The fluid communication conduit 16 thereby fluidly connects the first and third cavities 11 , 13 only when the third external groove 43 formed in the damping sleeve 5 overlaps the second end 16b of the fluid communication conduit 16. The fluid communication conduit 16 is thereby positioned to open into the third external groove 43 when the damping sleeve 5 is in a rearward position provided axially rearward of the floating position. The fluid communication conduit 16 is positioned such that the rearward position assumed during a drilling operation is a position different from a rearmost position of the damping sleeve 5. The rearmost position is a position defined by, e.g., a stopping surface of the housing 4, mechanically delimiting the movement of the damping sleeve 5 within the housing 4 when no hydraulic pressure is applied.

A size of the opening at the second end 16b depends on the axial position of the damping sleeve 5 with respect to the housing 4.

Thus, the fluid communication conduit 16 is arranged to open and fluidly connect the first cavity 11 to the third cavity 13 when the damping sleeve 5 moves axially rearward from its floating position, as shown in Fig. 3. It is further arranged to close and fluidly disconnect the first cavity 11 from the third cavity 13 when the damping sleeve 5 is in a forward position provided axially forward of its floating position, as shown in Fig. 4. A fluid return conduit 17, comprising a throttle 19, is further provided in the housing 4, axially forward of the first internal groove 31. The fluid return conduit 17 is positioned such that its opening is arranged to overlap with the first external groove 41 when the damping sleeve 5 moves forward from its floating position, as shown in Fig. 4. It is thereby arranged to open and release fluid from the first cavity 11 when the damping sleeve 5 moves axially forward from its floating position, and to be closed when the damping sleeve 5 is in a rearward position provided axially rearward of its floating position as illustrated in Fig. 3. It thereby opens only when the fluid communication conduit 16 is closed, and it is closed when the fluid communication conduit 16 opens. The fluid return conduit 17 may be connected to a tank (not shown). A size of the opening of the fluid return conduit 17 depends on the axial position of the damping sleeve 5 with respect to the housing 4. The fluid return conduit 17 is positioned to open into the first external groove 41 of the damping sleeve 5 when the damping sleeve 5 is in the forward position provided axially forward of the floating position. The fluid return conduit 17 is positioned so that the forward position assumed during a drilling operation is different from a foremost position of the damping sleeve 5, such as defined by a mechanical stop.

A front wall 21 of the first external groove 41 constitutes a first rearward facing pressure surface 21 of the damping arrangement 10, thus provided in the first cavity 11. A front wall 22 of the second external groove 42 constitutes a second rearward facing pressure surface 22, provided in the second cavity 12. The second cavity 12 is arranged to be pressurized via the first cavity 11 and via a narrow leakage slot 14 fluidly connecting the first cavity 11 to the second cavity 12. The first and second cavities 11 , 12 are dimensioned such that the second cavity 12 will be experienced as more rigid and less elastic than the first cavity 11 . This is achieved by providing the second cavity 12 with a smaller volume/area ratio than the first cavity 11 , wherein the area is the area of the respective pressure surfaces 21 , 22. In view of its smaller elasticity, the second cavity 12 is configured to provide a higher shock absorption response than the first cavity 11 and it will therefore act to absorb shockwaves generated during drilling. Thus, the second cavity 12 functions as a damping cavity. The first cavity 11 , comprising the first pressure surface 21 , will act as a working cavity, maintaining the floating position of the damping sleeve 5 as will be further explained below.

The leakage slot 14 is herein an annular slot provided between an inner surface of the housing 4 and an outer surface of the damping sleeve 5, although other configurations are possible. A fluid connection between the first cavity 11 and the second cavity 12, such as the leakage slot 14, should generally be dimensioned such that a desired damping is achieved.

During operation of the percussion piston 2, rock reflexes I shockwaves are generated, pushing the damping sleeve 5 in the rearward axial direction with respect to the housing 4, against the hydraulic pressure acting on the second pressure surface 22. As the damping sleeve 5 is pressed rearwards, both the first cavity 11 and the second cavity 12 will shrink, whereby the pressure increases in both cavities 11 , 12. Due to the configuration of the cavities 11 , 12, the second cavity 12 will experience a larger pressure increase. Leakage from the second cavity 12 to the first cavity 11 through the leakages slot 14 causes heating of the hydraulic fluid. At the same time, as the damping sleeve 5 is pressed rearwards, the third external groove 43 will move into an overlap with the second end 16b of the fluid communication conduit 16 and the conduit 16 will open, thereby providing a flow of pressurized hydraulic fluid to the first cavity 11. The force from both cavities 11 , 12 is thereby balanced against an applied feed force of the drilling machine 1 , minus the impulse of the percussion piston 2, and determines the direction of movement of the damping sleeve 5. As the pressure acting on the first and second pressure surfaces 21 , 22 increases, the damping sleeve 5 eventually starts to move forward. If the damping sleeve 5 moves far enough forward, the fluid return conduit 17 opens while the fluid communication conduit 16 closes. A controlled movement of the damping sleeve 5 around its floating position is thereby achieved.

The housing 4 illustrated in Fig. 2 further comprises a liner 7 in which the damping sleeve 5 is enclosed, and in whose inner perimeter the first, second and third internal grooves 31 , 32, 33 are formed. As further illustrated, the damping sleeve 5 has a first outer diameter d1 as measured axially forward of the first cavity 11 , a second outer diameter d2 as measured between the first and second cavities 11 , 12, and a third outer diameter d3 as measured axially rearward of the second cavity 12, wherein d1 > d2 > d3. In the illustrated embodiment, the fluid communication conduit 16 comprises an annular chamber 16c between the first end 16a and the second end 16c, functionally increasing the size of the first cavity 11. Furthermore, the first and second ends 16a, 16b of the fluid communication conduit 16 as well as the fluid return conduit 17 are in the illustrated embodiment located radially opposite to the fluid supply conduit 15. Since the first and third cavities 11 , 13 are annular, circumferential positions at which the fluid communication conduit 16, the fluid return conduit 17 and the fluid supply conduit 15 connect to the respective first and third cavities 11 , 13 need not match. The circumferential positions may be selected freely without affecting the function of the damping arrangement 10.

Although not illustrated in Fig. 2, a leakage slot is provided between the first cavity 11 and the second cavity 12, as illustrated in Figs. 3-4.

In the embodiment illustrated in Fig. 2, sealing rings 8 are further provided between the damping sleeve 5 and the liner 7. Hydraulic fluid chambers 9 intended for filtering pressure spikes and thereby protect the sealing rings 8 are also provided.

It is to be understood that the present disclosure is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.