FIELD OF THE INVENTION

The invention relates to a distribution valve for controlling hydraulic flows to different consumers, wherein the distribution valve includes a valve body being arranged movable to and fro in axial directions in a valve chamber, and wherein the valve chamber is limited in axial directions by a first and a second valve end wall. The invention also concerns a hydraulic rock drilling machine including such a device.

BACKGROUND OF THE INVENTION

Distribution valves for intermittently providing pressure fluid to different kinds of consumers as well as evacuating them are previously known for the use in a broad range of technical fields.

As concerns hydraulic percussive rock drilling machines, it is previously known to arrange a distribution valve which is controlled with the aid of a connection to the percussion device. The distribution valve aims to provide intermittent pressurizing of the drive chambers for the percussive piston for achieving the desired percussive effect. For that purpose the to and fro movable valve body is controlled with the aid of pilot pressure so as to transmit drive pressure to the drive chambers of the rock drilling machine.

Existing distribution valves for percussive rock drilling machines as well as for other uses function well at the frequencies and pressures of today's machines. Requirements for higher working frequencies, however, risk inducing

increased costs of the valve and thereby of the machine as a whole, since more sophisticated constructions of distribution valves with higher requirements for resistivity might be necessary. Also in respect of existing machines in the field of rock drilling and other technical fields there is a desire for valves that are developed for more reliable operation. AIM AND MOST IMPORTANT FEATURES OF THE INVENTION

It is an aim of the present invention to provide a further development of distribution valves as above and to provide an economically produced distribution valve that is applicable for demanding operation.

This aim is obtained in a device according to the above in that the valve body includes a central bore hole extending in axial direction which cooperates with a plunger being adjoining to the second valve end wall for forming of a pressurizable space, and that the plunger includes an outer piston portion having reduced diameter and being directed from the second valve end wall, which in an end position region of the valve body is arranged, together with a portion of the bore hole having corresponding reduced diameter, to cooperate in order to establish a damping chamber for end position damping of the valve body.

Hereby is achieved that the axial movement speed of the valve body can be effectively and safely cushioned in an end region of its movement range. This results in several

advantages over the background art such as:

- The impact force on a valve end wall will be lower. The strain on associated components will thereby be lower. The end position damping is advantageously provided for movements in directions of the most sensitive parts of the distribution valves that might risk to be damaged at impact with full speed of a valve body.

- The valve body can be allowed to have higher speed than otherwise during the main part of its movement between the end positions .

- Higher switching speed is thereby allowed which results in the possibility of increasing the frequency of a machine, such as a rock drilling machine, where the invention is used.

- By the damping chamber being arranged to work with a medium that is constantly pressurized, the risk of cavitation during return movement will be minimized.

- By the damping chamber being arranged to work with a constantly pressurized medium, damping will be obtained that is predictable and repeatedly securely calculated with an advantageously small damping chamber volume.

- Small volume of the damping chamber in turn gives a

possibility of making the damping chamber axially short such that the valve body can have a preferred high speed over the major part of its movement.

- The valve according to the invention can be simply and economically produced. Finishing machining of the valve body can be made in one machine set up which results in faster and more secure manufacture and achieving required tolerances more securely.

The portions of the bore hole as well as the portions of the plunger are circular cylindrical.

When a damping chamber is established, a damping slot advantageously exists between the outer piston portion and the portion of the bore hole having reduced diameter. In the damping slot there is a transformation of kinetic energy in through- flowing hydraulic medium into thermal energy in the hydraulic medium, which results in desired energy absorption. The person skilled in the art is within normal activities capable of dimensioning the damping slot for adaption to existing parameters such as speed and used hydraulic medium in order to secure that desired damping distance and damping characteristics are obtained.

Suitably, in or in the region of the first valve end wall, the valve includes a pressurizable chamber which receives a central end piston portion belonging to the valve body and being provided with an end surface for, in a

pressurized state of the chamber, driving the valve body in the direction of the second valve end wall. It is particularly preferred that in pressurized state of the space and pressureless state of the chamber, it is arranged for driving the valve body in the direction towards the second valve end wall .

It is preferred that the plunger is free from the second valve end wall. The plunger will then be pressed for lying against the second valve end wall by the pressure in said bore hole in the valve body and be allowed to be free from side force influence from the second valve end wall and instead be entirely guided by the bore hole. This results in minimized seize risk, since the plunger in a preferred manner is guided in radial direction against the valve body which in turn is guided by a valve lining/a valve housing, without creating any radial relative forces between the plunger and the valve body. This also allows manufacture with reduced tolerance

requirements and that snug throttle slot/damping slot as required can be arranged between the valve body and the plunger without the occurrence of seizing tendencies. The plunger is then in particular movable in a radial direction in respect of the second valve end wall when it is pressed against it.

The plunger can however be connected to the second valve end wall while allowing a relative movement in a radial direction in respect of the second valve end wall. Through this mutual mobility, it is allowed that the plunger to a certain extent can follow the movements of the valve body in a radial direction which at least reduces the seize risk. It is thinkable, but in most cases not suitable, that the plunger and the second valve end wall are rigidly immovably joined to each other. This is not preferred since with this solution there is a risk of seizing tendencies.

Into the bore hole there is preferably arranged at least one hole in a wall of the valve body in order to allow permanent pressurization of the space so as to facilitate permanent pressurization directly from one of the ports of the distribution valve. The permanent pressurization is preferably provided by a system pressure source being connected to the distribution valve.

The person skilled in the art suitably dimensions a relation cross section area/initial damping chamber volume (at just established damping chamber) after requirements and field of use for obtaining desired speed reduction at the same time as desired length of the damping distance.

The invention also concerns a hydraulic rock drilling machine with a machine housing which receives a working cylinder with a to and fro movable percussive piston wherein the rock drilling machine includes a valve according to the above .

Said valve is suitably received in the machine, resulting in advantages of integrating having to do with aspects

relating to manufacture and space. The distribution valve has an axis, preferably being parallel to an axis of the working cylinder, giving the possibility of building the rock drilling machine slim and space- saving.

It is also preferred that the rock drilling machine includes a housing end wall for the working cylinder, said housing end wall also closing a space receiving the

distribution valve. This results in that one single partition plane can be used for both the work cylinder and the

distribution valve, resulting in further reduced costs and advantages having to do with sealing aspects.

Further features and advantages of the invention are clarified in the following description of embodiments.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described in greater detail by way of embodiments and with reference to annexed drawings, whereon :

Fig. 1 shows a rock drilling machine equipped with a distribution valve according to the invention in an axial section,

Fig. 2 shows an enlarged section of a distribution valve according to the invention in a first position,

Figs. 3a and 3b show an enlarged section and a part enlargement of the distribution valve in Fig. 2 in a second position, and

Fig. 4 shows an enlarged section of the distribution valve in Fig. 2 in a third position.

DESCRIPTION OF EMBODIMENTS

In Fig. 1 is thus shown in an axial section a rock drilling machine 1 including a machine housing 2, wherein a percussive piston 3 is axially movable to and fro inside a cylinder space comprising a working cylinder 4. The percussive piston 3 performs impacts in an impact direction R against a shank adapter 5 in a per se previously known manner.

At the rear end region of the rock drilling machine 1 there is arranged a distribution valve 7 for distributing pressure fluid to the drive chambers of the rock drilling machine for driving the percussive piston 3 to and fro.

In Fig. 1 the distribution valve 7 is shown with its valve axis parallel to the axis of the percussive piston 3 and the working cylinder 4, being the axis of the percussion device of the rock drilling machine 1. This embodiment has the advantage that the rock drilling machine can be made slim and space saving at its rear part .

It also makes it possible for a rear housing end wall to be arranged to be in common for the working cylinder and the distribution valve such that an otherwise necessary partition plane can be dispensed of. Through this construction with parallel axes and common rear housing end wall is achieved the advantage of lower machining costs and thereby lower costs for the drilling machine. Furthermore, the risk of penetration of moist and impurities into the machine is reduced as well as the risk of failure because of unintentionally loosening screws .

In Fig. 2, the distribution valve 7 is shown in an enlarged scale, whereby is clarified that the distribution valve 7 has a valve body 8 being movable to and fro inside a valve lining 9, the valve body being movable between two end positions defined by stops against a first valve end wall 10 and a second valve end wall 11.

The valve lining 9 delimits a valve chamber 33 for receiving the valve body 8 and has the usual bores comprising channel ports for channels being connected to the distribution valve 7. The valve lining 9 is arranged with accurately defined control edges for cooperation with corresponding control lands on the valve body 8.

In the position shown in Fig. 2, the valve body 8 of the distribution valve 7 is positioned in a first end position with a first contact end 21 abutting against a first end stop 17 on the first valve end wall 10 of the valve body 8. The valve body 8 is in this position with a second contact end 22 at a distance from a second end stop 34 on the second valve end wall 11.

The position of the valve body in Fig. 2 occurs because of a chamber 14, which receives a central end piston portion

23 with an end surface 15, being a pressureless state.

Furthermore, a space 16 is arranged inside the valve body 8. Said space 16 is during operation permanently pressurized via holes 27 in the wall of the valve body from an equally permanently pressurized valve port.

The pressure in the space 16 acts against the end surface

24 of the space 16 and drives, in the pressureless state of the chamber 14, the valve body 8 to the left in the Fig. in the direction of its first end position.

The permanently pressurized space 16 is defined by a bore extending coaxially with the axis of the valve body. The axially second end of the space 16, opposite to the end surface 24, is limited by a plunger 35 extending sealingly into the bore hole, said plunger being pressed against the second valve end wall 11 by the pressure existing inside the space 16.

Between the bore hole and the plunger there is

furthermore, through a snug slit, sealing cooperation while allowing the valve body to be axially movable in respect of the second valve end wall and to the plunger.

The position shown in Fig. 3a has occurred because an intermittently pressurized channel (not shown) leading from a valve portion of the working cylinder 4 (Fig. 1) to the chamber 14, because of the position of the percussive piston 3 during its impact cycle, having been pressurized with system pressure. It should be noted that intermittently pressurizing the chamber 14 also can be realized in other ways.

Hereby the chamber 14 is pressurized such that a hydraulic pressure acts on the end surface 15 of the central end piston portion 23 of the valve body 8. Because of the area of the end surface 15 being greater than the area of the end surface 24 and typically the same pressure prevails in the chamber 14 and in the space 16, the valve body starts to be driven in the direction of its second end position and will after a certain time period be in the position shown in Fig. 3a.

With the valve body in the position shown in Fig. 3a, an outer piston portion 36 of the plunger 35, said outer piston portion 36 having a smaller diameter d compared to a larger diameter D of a main portion 37 of the plunger, has just reached a portion 38 of the bore hole with essentially the smaller diameter d (deviates somewhat because of a slot existing between the elements) . The main portion 37 of the plunger is in fact always in a portion 39 of the bore hole having (essentially) the greater diameter D (deviates somewhat because of a slot existing between the elements) . In this position of the valve body, through cooperation with the outer piston portion 36 and the portion 38 of the bore hole having the smaller diameter d, it is arranged that a damping chamber 40 will be established.

The damping chamber is as is shown in the detail enlargement in Fig. 3b essentially limited by:

- 42, a radially outward directed surface of the outer piston portion 36,

- 43, an axially directed end surface of main part of the plunger being positioned radially outside the outer piston portion 36,

- 44, an axially directed end surface of the portion of the bore hole with the greater diameter positioned radially outside the portion of the bore hole with the smaller

diameter,

- 45, a radially inward directed surface of the portion of the bore hole with the greater diameter.

During the continued movement of the valve body in the direction of the second valve end wall 11, from the position in Fig. 3a where the damping chamber 40 has been established all the way to where the valve body has reached its second end position, the volume of the damping chamber will decrease. Hydraulic medium being present in said damping chamber 40 will as a consequence thereof leak out in correspondence to the volume reduction through a damping slot 41 formed between an envelope surface of the outer piston portion 36 being directed radially outward and an inside surface of the portion 38 of the bore hole with smaller diameter.

The hydraulic medium will thereby leak out through the damping slot 41 against the pressure inside the permanently pressurized space 16 inside the valve body 8. The damping is effected by the kinetic energy in the valve body being transformed to heat absorbed by the hydraulic medium during the passage thereof through the damping slot. Hydraulic medium inside the damping chamber will

essentially be pressed out through the damping slot 41 but also to a lesser degree as leakage between the slot formed between the main part 37 of the plunger and the portion 39 of the bore hole having greater diameter.

In the second end position of the valve body 8 shown in Fig. 4, the valve body 8 is in contact with the second contact end 22 against the second end stop 34 on the second valve end wall 11.

Starting up from this position, pressurization of the chamber 14 is terminated and the chamber is instead connected to a return channel/to the atmosphere/to a lower pressure, whereby the valve body is again driven towards the position shown in Fig. 2 whereupon the above described movement pattern is repeated.

The invention can be modified within the scope of the claims. As an alternative or complimentary to the arrangement with the damping slot 41, it is possible but not preferred to have a channel 46 connected to the damping chamber (is

indicated with interrupted line in Fig. 4) , wherein a damping throttle 47 is arranged which can be fixed or adjustable. This gives the possibilities of control and reduces requirements for dimensioning the damping slot.

In order to reduce tendencies of cavitation, it is possible but not preferred to connect a pressure source P for supplying hydraulic medium with the same pressure as prevails in the space 16 to the damping chamber. In a channel 48

(indicated with interrupted line in Fig. 4) from this pressure source is suitably inserted a one way valve being open in a direction towards the damping chamber.

The first as well as the second valve end wall 10, 11 can be movable such that both valve end walls can be pressed against stops in the direction of each other for defining two defined end positions for the valve body 8. It is however within the scope of the invention that the valve end walls are attached to the valve housing in a conventional manner through for example screwing, bolting, being inserted and locked cross wise etc.

The distribution valve 7 can be manufactured also without a specific valve lining 9.

The invention is, as is explained above, also applicable for more conventionally constructed distribution valves having fixed valve end walls. One or both valve end walls can further also be integrated in a housing for the distribution valve, wherein with "valve end wall" is to be understood an end wall of a valve chamber.

With the term "pressureless state" of the chamber 14 is intended that the chamber is disconnected from high pressure/ system pressure and instead has been connected to low pressure or atmosphere pressure.

The invention has been described at the background of a hydraulic rock drilling machine but the person skilled in the art of control technology realizes that the invention is applicable for distribution valves for controlling hydraulic flows to different consumers also within other technical fields besides rock drilling. The invention is therefore valuable within all kinds of technical fields where the advantages mentioned in the general part of the description above can be exploited such as for example: lower degree of strain during operation, higher switching speed, lower risk of cavitation, predictable damping, small volume of the damping chamber, good production economy.