WO1993017835A1

WO1993017835A1 - Pressure medium operated impact mechanism

Info

Publication number: WO1993017835A1
Application number: PCT/SE1993/000197
Authority: WO
Inventors: Göran Nilsson; Roland Berg; Kjell EDSTRÖM
Original assignee: Nilsson Goeran; Roland Berg; Edstroem Kjell
Priority date: 1992-03-09
Filing date: 1993-03-08
Publication date: 1993-09-16
Also published as: TW241216B; SE469971B; SE9200710L; SE9200710D0

Abstract

A pressure medium operated reciprocating impact mechanism has a working member (7) and a stop member (15), which are axially movable with respect to each other, and a working chamber (22) for pressure medium is arranged in at least a first one of them and is open towards the other member. A sealing member (21) is arranged inside the working chamber between the working member and the stop member and to bear radially against the circumferential wall (14) of the working chamber and seal the working chamber in that position of the relative movement of these members in which they are brought most together. The sealing member is adapted to, on movement of the working member and the stop member apart starting from said position and caused by action of the pressure medium entering into the working chamber, move axially with respect to one of these members while bearing sealingly against the circumferential wall (14) of the working chamber and axially sealing the working chamber to the other of these members. One of the working and stop members has means (25, 29) adapted to allow the pressure medium to escape out of the working chamber when the other of said members has reached a position located at a predetermined distance from the position thereof in which said members are brought most together.

Description

FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a pressure medium operated reciprocating impact mechanism according to the preamble of the appended claim 1.

Impact mechanisms of this type may be used for pressure medium operated devices working by a reciprocating movement of most various types and sizes and widely different ranges of the size and frequency of the impact movement or stroke. Devices for driving down and in objects, such as poles and tongues, for drilling, chiselling, engraving, hammering, vibrating screens, feed shoes and similar devices as well as compacting ballast masses etc. may be mentioned as examples. Another common field of use is as slag hacker.

Impact mechanisms of this kind are known for example by the Swedish patents 7503970-1 and 7603252-3 of the applicants, and although the impact mechanisms described therein function well, the length of the stroke of the working member is not so exactly definable as it would sometimes be desired, but it is for example dependent on the pressure of the medium in question and it does accordingly vary with fluctuations thereof. Besides that the length of the srroke is not exactly

SHEET definable it is also, despite that it may be increased by choosing a weaker spring between the working member and the housing of the tool in question, toι- short for certain ap¬ plications, since the pressure medium leaves the working chamber as soon as the sealing member leaves the contact with either the bottom of the working chamber or said second of said members. A shorter length of the stroke has the conse¬ quence that the frequency tends to get to high for certain applications, whereby local points with very high tempera¬ tures in the working tool in question may be created, and the the working life of said tool may by that be considerably shortened by premature material fatigue. This is for example valid especially when using the impact mechanism for carry¬ ing out sawing movements and the like, since only a very re¬ stricted part of for instance a saw blade is then utilized and exerted to a high frequency.

BRIEF DESCRIPTION OF THE INVENTION

The object of the present invention is to provide an impact mechanism of the kind mentioned in the introduction, which enables to exactly define the length of the stroke of the mechanism substantially independently of the pressure of the pressure medium driving the tool as well as obtain large lengths of the stroke with respect to the dimensions of the sealing member if so is desired.

This object is according to the invention obtained by an im¬ pact mechanism of the kind mentioned in the introduction, in which the sealing member is adapted to, on movement of the working member and the stop member apart caused by action of the pressure medium entering into the working chamber, move axially with respect to one of these members while bearing sealingly against the circumferential wall of the working chamber and axially sealing the working chamber to the other of these members, and that one of the working and stop mem¬ bers has means adapted to allow the pressure medium to es- cape out of the working chamber when the other of said members has reached a position located at a predetermined distance from the position thereof in which said members are brought most together.

Thanks to the axial mobility of the sealing member with re¬ spect to one of the working and the stop members and the ar¬ rangement of said pressure medium escape means, there is obtained on one hand a very exactly defined length of the stroke and on the other that the length of the stroke may be given almost every size desired by suitable location of the pressure medium escape means.

The distance between the working and the stop members, at which the pressure medium is allowed to leave the working chamber, is in the impact mechanisms previously known depend¬ ent on the pressure of the pressure medium, since the axial extension and by that the sealing action of the sealing mem¬ ber is dependent on the pressure prevailing, whereas the sealing member in the device according to the invention has moved axially with respect to the working and stop members while bearing sealingly against the circumferential wall of the working chamber and axially sealing the working chamber to the other of the said members and got a shape considerably less dependent on the medium pressure when this other member reaches the position in which the pressure medium is allowed to escape out of the working chamber.

According to a prefeered embodiment of the invention the sealing member is arranged to, on movement of the working member and the stop member apart caused by action of the pressure medium entering into the working chamber starting from said position in which the members are brought most together, follow said other of these members while moving axially along the circumferential wall of the working chamber, and the circumferential wall of the working chamber has means adapted to allow the pressure medium to escape out of the working chamber when the sealing member has reached a position located at a predetermined distance from the position thereof in which said members are brought most together.

According to a further preferred embodiment of the invention said pressure medium escape means comprise at least one open¬ ing arranged radially in the circumferential wall of the working chamber, and this opening is preferably supplemented by an increase of the cross-section of the working chamber, so that the radial as well as the axial sealing of the work¬ ing chamber by the sealing member are simultaneously inter¬ rupted and the ceasing of the stroke gets more distinct and well defined.

Tools provided with the impact mechanism according to the in¬ vention get by that a more smooth function and they are ac¬ cordingly obtaining a result of a higher quality than tools provided with the impact mechanisms previously known on proc¬ essing surfaces and the like. Tools provided with this type of impact mechanisms get thanks to the achievable increased length of the stroke new possible fields of use, where a greater length of the stroke is almost a condition, such as sawing and the like.

Further advantages as well as preferred characteristics of the invention will appear from the following description and the other dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a de¬ scription of a preferred embodiment of the invention cited as an example. In the drawings:

Fig. 1 is a side view of a tool provided with a pressure me¬ dium operated impact mechanism according to the invention. Fig. 2 is a longitudinally sectioned view of the tool shown in fig. 1, which is enlarged compared with fig 1 and illus¬ trates the construction of an impact mechanism according to a preferred embodiment of the invention.

Fig. 3 is a partially sectioned partial view, which is en¬ larged with respect to fig. 1 and 2 and illustrates the con¬ struction of the working chamber and the sealing member in the impact mechanism shown in fig. 2 with the working member and the stop member in the position in which they are brought most together, and

Fig. 4 is a view substantially corresponding to fig 3, but with the working member and the stop member moved apart into substantially the opposite extreme position.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVEN¬ TION

A tool 1 is shown in fig 1, which in an exemplifying but not limiting way is provided with a saw 2 , arranged to carry out a reciprocating movement thanks to the impact mechanism ac¬ cording to the invention arranged inside the casing 3 of the tool. The tool has at one end thereof a means 4 for connec¬ tion of pressure medium, in this case air through a hose 5 cut off in figure for space reason, and a conduit 6, preferably a flexible plastic hose, for leading consumed pressure medium away. Thanks to the fact that all pressure medium consumed is led through the conduit 6 away from the working place and not, which is usually the case for this type of tools, flows out in the region of the opposite end of the tool, the working condition is considerat-^' improved for the person handling the tool by a reduction of the noise level and the whirling up of dust. It will hereafter for the sake of simplicity always be referred to compressed air. although other types of pressure medium are of course also comprised.

With reference to fig 2, the construction of the impact mechanism according to the invention and arranged inside the tool 1 will now be described. It consists in a conventional way of a reciprocating working member 7 axially guided inside the casing 3, at one free end 8 of which different types of working tools, such as small saws, chisels and the like may be secured by inserting a small rod thereof between jaws 9 of the working member and after that tightening a nut 10. The working member 7 comprises at its opposite end a plate 12 secured by a screw to the elongated part 11 of the working member with a circular bottom 13 turned in the axial direction away from said end 8 and circumferential walls 14 with a cylinder casing shape projecting substantially perpendicularly therefrom in the same direction. A stop member or balance body 15 is arranged guidingly displaceable in the axial direction along an elongated body 32 received at the end 16 of the tool for supply of compressed air and extends into the room inside the circumferential wall 14 of the plate while being axially guided also through guide means in the form of O-rings 17, 17' , which bear against the interior wall of the casing as well as the circumferential wall 14 (a ring 17'). The elongated body 32 is also guided with respect to the casing 3 through an O-ring 17.

The working member 7 and the stop member 15 are influenced in the direction towards each other by a compression spring 18 and 19, respectively, each which are adapted to act between axially directed surfaces of the casing and the respective member and in a rest position in absence of compressed air in the connection means 4 hold the stop member 15 with the axi¬ ally directed front surface 20 thereof preloadedly bearing against a sealing member 21, here in the form of a conven¬ tional elastic O-ring, bearing against said bottom 13. The impact mechanism described so far is except for the very construction of the plate 12 already known, and the new and characteristic features of the impact mechanism according to the invention, namely the way to determine the length of the stroke of the working member, will now be described with ref¬ erence to fig 3 and 4.

A position in which the working member 7 and the stop member 15 are maximally brought together and which substantially corresponds to said rest position is illustrated in fig 3. A working chamber 22 sealed with respect to the exterior is in this position formed between said bottom 13 and the axial surfaces of the stop member turned towards said bottom. The sealing member 21 bears radially tight against the circumfer¬ ential wall 14 and axially seals the working chamber 22 be¬ tween the stop member and the circumferential wall. The seal¬ ing member 21 is in this position somewhat deformed by the forces trying to press the working member and the stop member towards each other.

The body 32 has an inner channel 23, which at one end thereof opens towards the means 4 for connection of compressed air and in the opposite direction continues in the stop member 15 and at its other end 24 emerges into the working chamber 22 (see also fig. 2). When supplying compressed air through the channel 23 to the working chamber 22, this compressed air will press the working member 7 and the stop member 15 apart, so that the working member 7 moves forwardly against the ac¬ tion of the spring 18, at the same time as the stop member 15 moves in the opposite direction against the action of the spring 19.

The sealing member 21 is arranged freely movable in the work¬ ing chamber and will during this movement apart be pressed by the compressed air radially against the circumferential wall and at the same time axially against axial surfaces 20 of the stop member and by that follow the stop member in the move- ment thereof while maintaining the sealing of the working chamber 22 with respect to the exterior. The bottom 13 of the working chamber is preferably formed by a lubricated Teflon- washer, so that the sealing member may easily be released from the bottom on the movement of the working and stop mem¬ bers apart. The circumferential wall 14 of the working cham¬ ber 22 is provided with circuraferentially evenly distributed through bores 25 at a distance from the bottom .13 of the working chamber. When the sealing member (the O-ring 21) in said movement of the working member 7 and the stop member 15 ■ apart with its radial bearing surface reaches the limitation 26 closest to the bottom 13, the radial sealing of the seal¬ ing member will be interrupted through said bores 25 (see the position according to fig. 4) , and the compressed air present in the working chamber 22 may flow past the sealing member 21 and out of the bores 25. A free room 27 is located between the plate and the casing outside the circumferential wall 14 of the plate. The compressed air may then move to the outlet 6 through said free room and because the stop member on one side is provided with a slot 28. This leads to that now only the two compression springs 18 and 19 act upon the working member 7_.and the stop member 15, respectively, so that the movement apart after a neglectable continuation is trans¬ formed to an opposite movement together. The sealing member 21 will then be pushed towards the bottom 13 of the working chamber and sealing this again, whereupon compressed air is supplied to the working chamber so created and presses that working and stop members apart, which then have reached the position according to fig. 3, with the sealing member 21 de¬ formed.

The circumferential wall 14 of the working chamber 22 has at the level of said limitations 26 of the bores 25 closest to said bottom 13 a diameter increase concentrically made, so that the circumferential wall has a wall portion 29 extending from the limitations 26 away from the bottom 13 and having a greater interior diameter than the wall portion 30 located closer to the bottom 13. When the sealing member 21 in the movement apart with the radial bearing surface thereof bear¬ ing against the circumferential wall reaches said limitation, the diameter increase of the circumferential wall will cause an interruption of the axial sealing between the circumferen¬ tial wall and the stop member, so that compressed air present in the working chamber may axially flow past the sealing member 21 and here out of the bores 25. Thanks to the co¬ operation of the bores 25 and the cross-section increase of the circumferential wall a very abrupt, distinct and powerful or large opening of the working member previously sealed is obtained. Thus, this co-operation leads to that the end of the stroke of the working member and by that the length of the stroke of the tool becomes well defined. The length of the stroke of the tool is in this way not dependent on the dimensions of the sealing member or the pressure of the compressed air as in the impact mechanisms according to the prior art, but the position of the bores 25 and the cross- section increase of the circumferential wall 14 determine the length of the stroke, and the length of the stroke may thanks to this in advance be chosen according to the application the tool is intended to have by locating these compressed air escape means at an appropriate distance from the bottom 13 of the working chamber. It would then also be conceivable to provide a tool of this kind with a set of different plates 12 for shifting plate by activating the screw 31 for varying the length of the stroke of the tool.

Thus, not only an impact mechanism with a well defined length of the stroke is obtained by the invention, but this length of the stroke may also be given every length desired by suit¬ ably dimensioning the working chamber and locating the compressed air escape means. By the greater length of the stroke achievable in this way in the impact mechanism with the respect to those already known, a tool equipped therewith may be used in working situations in which a comparatively great length of the stroke and a lower frequency are desired. It is not required that the compression springs 18 and 19 are made weaker or softer for the obtainment of this lower frequency as in the impact mechanism already known, but the increased length of the stroke ensures this. An example of such a use is sawing of small contures, since a greater part of the saw blade may be utilized in this way and a generation of high temperature for the saw blade material is avoided.

The well defined length of the stroke results in a clearly improved function and an increased efficiency of the tool • when using it for example as slag hacker so as to for example hack welding slag or the like away, but this well defined length of the stroke has of course advantages in all kinds of conceivable applications of a tool provided with an impact mechanism of this type.

As an example of dimensions of a tool of the kind shown in the figure the following may be mentioned: the interior di¬ ameter of the circumferential wall 20 ram's, the cross-section of the O-ring 2 mm's, the distance between the bottom 13 and the limitation 26 3 mm's, the diameter of the bores 25 2 mm's, the interval between the bores 25 2 mm's, the increase of the diameter of the working chamber at the limitation 26 0,3 mm. Such a tool gets a length of the stroke of 4 mm's. The frequency of the tool will be about 221 strokes per second.

The invention is of course not in any way restricted to the preferred embodiment described above, but several possibili¬ ties to modify it would be apparent to a man skilled in the art without departing from the basic idea of the invention.

It would for example be well possible to have only bores in the circumferential wall of the working chamber or a cross- section increase thereof as pressure medium escape means, wherein in the latter case it is necessary that the pressure medium is then allowed to pass the stop member axially. The or the like. The cross-section increase could also be par¬ tial, so that the cross-section could for example be in¬ creased at intervals along the circumference of the circum¬ ferential wall, so that for example axially extending slots beginning at said limitation 26 could be arranged in the cir¬ cumferential wall.

It would be conceivable that the working chamber has another cross-section shape than circular, and the sealing member has then to be designed in the corresponding way. The bottom and the circumferential walls of the working chamber could also be arranged on the stop member and the end of the working member directed thereto could be designed in adaption thereto.

The sealing member could be fixedly arranged on the member movable with respect to the circumferential walls of the working chamber, the stop member in the case shown, and it would then also be conceivable to arrange a separate spacer secured to the bottom of the working chamber so as to define the position in which the members are brought most together and a sealing member surrounding the. member movable with respect to the circumferential wall while radially bearing against the circumferential wall and axially sealing the working chamber.

A practically complete balancing of the mechanism is achieved thanks to the arrangement of the compression springs and it is also resiliently arranged in the tool casing, so that firstly no or insignificant vibrations are transferred to the casing, when the tool is in no-load operation, and secondly no harmful vibrations are either transferred to the casing when the tool is applied against a working surface for chis¬ elling or the like. However, it would also be conceivable to omit this devibration and arrange the stop member fixed with respect to the casing, so that the relative movement of the working member and the stop member is obtained only by a movement of the working member.

Claims

1. A pressure medium operated reciprocating impact mechanism having at least one working member (7) in the form of a pis¬ ton or the like and at least one stop member {15) , which are axially movable with respect to each other, and a working chamber (22) for pressure medium is arranged in at least a first one of them and is open towards the other member, a sealing member (21) being arranged inside the working- chamber between the working member and the stop member and to bear radially towards the circumferential wall (14) of the working chamber and seal the working chamber in that position of the relative movement of these members in which they are brought most together, c h a r a c t e r i z e d in that the sealing member is adapted to, on movement of the working member and the stop member apart starting from said position and caused by action of the pressure medium entering into the working chamber, move axially with respect to one of these members while bearing sealingly against the circumferential wall (14) of the working chamber and axially sealing the working chamber to the other of these members, and that one of the working and stop members has means (25, 29) adapted to allow the pressure medium to escape out of the working chamber when the other of said members has reached a position located at predetermined distance from the position thereof in which said members are brought most together.

2. A Mechanism according to claim 1, c h a r a c t e r i z e d in that the sealing member (21) is arranged to, on movement of the working member and the stop member apart caused by action of the pressure medium entering into the working chamber starting from said position in which the members are brought most together, follow said other of these members while moving axially along the circumferential wall (14) of the working chamber, and that the circum- ferential wall of the working chamber has means (25, 29) adapted to allow the pressure medium to escape out of the working chamber when the sealing member has reached a posi¬ tion located at a predetermined distance from the position thereof in which said members are brought most together.

3. A mechanism according to claim 2, c h a r a c t e r i z e d in that said pressure medium escape means comprise at least an opening (25) arranged in the cir¬ cumferential wall (14) of the working chamber at a predeter¬ mined distance from the bottom (13) of the working chamber directed substantially axially and towards said other means, said opening being arranged to, when the sealing member with its radially bearing against said circumferential wall reaches the limitation (26) of said opening closest to said bottom, interrupt the radial sealing of the sealing member (21) with respect to the circumferential wall (14) and be connected to the working chamber (22) for letting the pressure medium out therefrom.

4. A mechanism according to claim 2 or 3, c h a r a c t e r i z e d in that said pressure medium escape means comprise an increase (29) of the cross-section of the working chamber made at least along a part of the circumfer¬ ence at a predetermined distance from the bottom (13) of the working chamber directed substantially axially and towards said other member (15), said increase being arranged to, when the sealing member on movement of the working member and the stop member apart by its radial bearing against said circumferential wall (14) reaches the limitation (26) of said increase closest to said bottom (13), interrupt the axial sealing by the sealing member (21) of the circumferential wall (14) with the respect to said other member (15) and al¬ low the pressure medium to leave the working chamber (22) by passing the sealing member.

5. A mechanism according to any of the claims 2-4, c h a r a c t e r i z e d in that a sealing member (21) is arranged freely movable in the working chamber (22) and to be pressed by the pressure medium present in the working chamber against surfaces (20) of said other (15) of said members di¬ rected substantially axially and towards the bottom (13) of the working chamber so as to follow this member in the move¬ ment thereof with respect to the circumferential wall (14) of the working chamber.

6. A mechanism according to any of the claims 2-5, c h a r a c t e r i z e d in that said other (15) of said members has surfaces (20) directed substantially axially and towards the bottom of the working chamber, and that the seal¬ ing member (21) is adapted to act as a spacer between said surfaces and the bottom (13) of the working chamber and de¬ fine the position in which the working and stop members are brought most together by being axially pressed by said sur¬ faces against said bottom in this position.

7. A mechanism according to claims 3 and 4, c h a r a c t e r i z e d in that the limitation (26) of the opening (25) closest to the bottom (13) of the working chamber and the cross-section increase (29) of the circumferential wall are located at substantially the same distance from said bottom (13) so as to substantially simultaneously interrupt the radial and axial sealing of the sealing member (21) to the circumferential wall (14) of the working chamber.

8. A mechanism according to claim 3, c h a r a c t e r i z e d in that the pressure medium escape means comprise a plurality of substantially equally large openings (25) substantially regularly distributed around the circumferential wall, which are arranged at substansially the same distance from the bottom (13) of the working chamber and radially directed.

9. A mechanism according to claim 8, c h a r a c t e r i z e d in that the openings (25) have a substantially circular cross-section.

10. A mechanism according to claim 4, c h a r a c t e r i z e d in that the circumferential wall (14) of the working chamber has the shape of substantially a cylinder casing and that said cross-section increase (29) is formed by a diameter increase of the cylinder casing carried out concentrically and being substantially step-like.

11. A mechanism according to any of the claims 1-10, c h a r a c t e r i z e d in that the sealing member is a conventional O-ring (21) of elastic material and has in the unloaded state thereof substantially the same outside diameter as the inside diameter of the working chamber (22) in connection with the bottom (13) thereof.

12. A mechanism according to claim 8 or 9, c h a r a c t e r i z e d in that each opening (25) has sub¬ stantially the same cross-section area as the cross-section area of the sealing member (21) in an axially directed plane.

13. A mechanism according to claim 8, c h a r a c t e r i z e d in that the circumferential dis¬ tance between two consecutive openings (25) corresponds sub¬ stantially to the greatest dimension of each of the openings in the circumferential direction.