Patent Application
20150290788
The invention relates to a percussion device for a hydraulic rock drilling machine including a to and fro moveable impact piston, which is provided with a land portion for co-operation with a braking recess in advanced positions of the impact piston relative to a normal impact position, wherein a throttle slit is established between wall portions of the land portion and the braking recess, and wherein the percussion device includes a piston guiding device which is positioned in front of the braking recess. The invention also relates to a hydraulic rock drilling machine including such a percussion device.
It is previously known in percussion devices for hydraulic rock drilling machines to provide the cylinder of the percussion device with a brake recess. In certain operational conditions a land portion of the impact piston of the percussion device enters this brake recess for the establishment of a braking chamber. Such operational conditions are when the shank adapter of the percussion device because of reduced resistance has been displaced forward in the impact direction, such that the strike of the impact piston against the shank adapter no longer occurs within the region of a desired impact position.
The aim of arranging a brake recess in the cylinder and the co-operating land portion on the impact piston for then establishment of a braking chamber is to decelerate the impact piston in order to at least limit the intensity of impacts against the shank adapter in too far advanced positions thereof. Such impacts otherwise risk resulting in damaging the drilling machine.
The brake recess, which is filled with hydraulic medium, is subjected to an instantaneous pressure increase when a land portion on the impact piston enters therein, resulting in that hydraulic medium under pressure is transmitted on the one hand over a throttling slot being established between wall portions of the land portion and the braking recess, on the other hand forward from the established braking chamber towards and passed the piston guiding device to a draining chamber which is optionally arranged in front of the piston guiding device.
Further, after contact of the impact piston with the shank adapter, a fast return movement of the impact piston will occur, leading to cavitation in the hydraulic medium in the established braking chamber and all the way in between the impact piston and the piston guiding device. This risks damaging the piston guiding device, which usually is made from a relatively soft bearing material.
In order to reduce these problems it has been suggested to form the land portion with a surrounding flange and to form the braking recess correspondingly larger such that a greater volume of oil is activated during braking. This results in a lower pressure in the established braking chamber and thereby reduced damages to the piston guiding device and the seals. The previously known solution also allows the throttle slit between the land flange and the co-operating wall portion of the braking recess to be formed with somewhat increased area, which in turn reduces cavitation risks in case of a rebounding impact piston.
The background art referred to reduces the above problems but brings along some other drawbacks such as increased cylinder dimensions, which is intended to be addressed with the present invention.
The aim of the present invention is to provide a percussion device as mentioned initially wherein the problems of the background art are at least reduced and wherein an effective and economically manufactured percussion device is obtained.
This aim is obtained according to the invention with a percussion device as mentioned initially in that a pressure channel, being connected to a pressure medium source, is arranged to debouch in the cylinder between the piston guiding device and the land portion in a position thereof in a most advanced position of the impact piston.
Hereby the drawbacks of the above described background art are avoided since the inventive percussion device becomes more energy-effective because a land flange consuming energy when its moves as a part of the impact piston during normal drilling can be avoided. Better drilling efficiency can thereby be expected with the inventive percussion device. The invention allows more effective reduction of cavitation problems that after all partly remain in respect of devices according to the closest background art.
Such advanced positions occur during so called idle strikes of the percussion device and can also occur during drilling when a cavity or weak rock is met, and for example when the drilling machine is used for scaling purposes. The shank adapter has then advanced forward from its normal position during normal drilling.
It should be noted that with the expression: “a pressure channel connected to a pressure medium source is arranged to debouch in the cylinder” is intended that the pressure channel can open in the cylinder via a room or a recess and not that the pressure channel necessarily has an opening in the very surface of the cylinder receiving the impact piston.
With the expression: “most advanced position of the impact piston” is intended a position which is either limited purely mechanically, in that the shank adapter has reached a position against a stop in the rock drilling machine housing or in any other way is a most advanced position (as seen in the impact direction) that can be reached by the impact piston. Hereby is ensured that an opening of the pressure channel in the cylinder e.g. does not risk being blocked by a portion of the impact piston in any position of the impact piston.
Through the invention is achieved a pressure equalization in the region between the land portion, in its most advanced position, and the piston guiding device. Since further the invention in practice results in supply of hydraulic medium, it is achieved that cavitation in the region of the piston guiding device is reduced. Hereby also the working life of the piston guiding device can be expected to increase because of enhanced lubrication.
It is preferred that the pressure channel is arranged to debouch in an equalizing chamber being arranged between the braking recess and the piston guiding device, since this arrangement in an effective way reduces cavitation at the piston guiding device as well as also reduces pressure peaks affecting the sealing device. Altogether, according to this aspect of the invention increased working life of the piston guiding device and the piston seal is obtained. Compared to the background art, also best efficiently is obtained since the land portion can be formed with a small radial extension. In particular it is preferred that the equalizing chamber is ring-shaped.
The region of the cylinder between the braking recess and the equalizing chamber is suitably formed with such a slit that a slit throttling is formed vis-à-vis the impact piston in order to obtain an effective energy absorption at the same time as a certain oil flow could occur from the equalizing chamber to the braking recess during the movement of the impact piston opposite to the impact direction.
It is preferred that the braking recess, the piston guiding device and the equalizing chamber are arranged in a piston guiding unit being arranged in a housing of the rock drilling machine. This simplifies manufacture and makes manufacture more economic with maintained strict tolerances. Suitably also a draining chamber and impact piston seals are arranged in the piston guiding unit.
As a variant, the pressure channel is instead arranged to debouch in a region of the braking recess being positioned most closely to the piston guiding device. This arrangement is less effective than the above described but has i.a. the advantage of reduced machining effort and the possibility of reduced machine length. Suitably, in the pressure channel there is arranged a one way valve which is open in a direction of a mouth in the braking recess in order to avoid an intentional draining in this region and in order to ensure that the brake pressure is maintained at an expected level.
The pressure medium source suitably any one from the group: a drive chamber in the percussion device, which is normally preferred because of essentially direct accessibility, a supply channel for percussion pressure, which is suitable in case it is desired to avoid oil take out from the drive chamber, a separate high pressure generator, which gives certain regulating possibilities.
The provision of a regulating device in order to regulate pressure and/or flow in the pressure channel makes adjustment to different operational situation possible.
In an embodiment, the land portion co-operating with the braking recess includes a radially extending land flange, which results in reduced pressure build-up in the braking recess but also risk for increased radial dimensions of the cylinder.
The invention also concerns a corresponding method for the operation of a percussion device of a hydraulic rock drilling machine, wherein hydraulic medium from a pressure medium source is supplied in the cylinder between the piston guiding device and a position of the land portion in a most advanced position of the impact piston.
Method features corresponding to the above subordinate device features are applicable for variants of this method.
The invention will now be described in greater detail by way of embodiments and with reference to the annexed drawings, wherein:
Like and similar elements have in some cases been given same reference signs.
In
The braking recess 11 is arranged to co-operate with a land portion 12 being shaped as a radial extension of the impact piston 3 in advanced position of the impact piston 3 for establishment of a braking chamber.
The piston guiding unit 7 further includes an equalizing chamber 13, which is arranged between the braking recess 11 and the piston guiding device 6 and which communicates with a permanently pressurized drive chamber 15 arranged for return strokes of the impact piston 3. A pressure channel 14 is provided for ensuring a supply of hydraulic medium from the drive chamber 15 to the equalizing chamber 13.
As seen in the impact direction R in front of the piston guiding device 6, there is a draining chamber 9, also being received by the piston guiding unit 7, for draining hydraulic medium/pressure medium escaping passed the piston guiding device 6. In front of the draining chamber 9, as seen in said impact direction R, is further positioned a sealing device 8, which in this embodiment includes two axially separated piston seals. Other configurations of the sealing device can exist.
In
In
Such advanced positions occur during idle strikes of the percussion device and can also occur during drilling when the drill bit meets a cavity or weak rock, and for example when the rock drilling machine is used for scaling purposes. The shank adapter has then been able to advance forward in the impact direction from its normal position during normal drilling operation.
When the land portion 12 of the impact piston enters into the braking recess 11 and the braking chamber is established, a high pressure is formed aiming to decelerate the impact piston. This high pressure leads to the escape of hydraulic medium from the braking recess on the one hand through the throttle slit 17, on the other hand through a throttle slit 16 formed between the impact piston 3 and an inwardly directed ring surface between the braking recess and the adjacent equalizing chamber 13.
With an interrupted line at 28 is in
Through the pressure medium supplied equalizing chamber 13, potential pressure peaks emanating from the entry of the land portion into the braking recess are effectively reduced, pressure peaks that would otherwise be harmful for the sealing device. Further is achieved, through supplying hydraulic medium through the pressure channel 14, that cavitation effects on the piston guiding device are effectively reduced during return strokes of the impact piston.
As an alternative to being comprised of an integral component, the piston guiding unit can be comprised of plural, for example two, three or more parts which together are insertable into the cylinder. Each one of these parts can exhibit one or more of the different elements: the piston guiding device 6, the braking recess 11, the draining chamber 9, the sealing device 8 and the equalizing chamber 13.
In
In the variant in
19 indicate a one way valve, which is positioned in the pressure channel 14′ in order to prevent a back-flow of hydraulic medium during the instantaneous pressure increase occurring when the land portion 12 with high speed enters into the braking recess 11.
The invention can be modified within the scope of the following claims.
It is possible to provide hydraulic medium in different ways to the pressure channel, wherein the variant illustrated in
The cylinder of the rock drilling machine can be constructed otherwise and the braking chamber can be received directly in the housing instead of, as is shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 1251341-2 | Nov 2012 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2013/051265 | 10/30/2013 | WO | 00 |
