US2838032A - Explosively actuated impact tool with free-piston - Google Patents

Description

June 10, 1958 G. SCHULIN ETAL 2,838,032

EXPLOSIVELY ACTUATED IMPACT TOOL WITH FREE-PISTON Fil ed Aug. 1, 1955 J 3 Sheets-Sheet 1 your-ad fi czeye 1' M m June 10, 1958 G. SCHULIN ETAL 3 EXPLOSIVELY ACTUATED IMPACT TOOL WITH FREE-PISTON 5 Sheets-Sheet 2 Filed Aug. 1, 1955 United States Patent EXPLOSIVELY ACTUATED IMPACT TOOL WITH FREE-PISTON Gotthilf Schuiin, Fellbach, Wurttemberg, and Konrad Haage, Esslingen, Wurttemberg, Germany, assignors to Delmag-Maschinenfabrik Reinhold Dornfeld, Esslingen (Neckar), Germany Application August 1, 1955, Serial No. 525,451

Claims priority, application Germany August 11, 1954 16 Claims. (Cl. 123-7) The present invention relates to impact tools and, more specifically, to explosively operated impact tools with free-piston. Tools of this type generally operate in such a manner that the explosively actuated free-piston acting upon a work tool such as a chisel is returned to its starting position either by a spring or by gas under pressure furnished by a compressor or by a bottled gas cylinder.

The heretofore known explosively actuated impact tools with free-piston have the drawback thatit is more or less cumbersome to start such tools. Consequently such tools are not ready for operation in an instant but require certain operations for starting in contrast to impact tools operated by compressed air.

It is, therefore, an object of the present invention to provide an explosively actuated impact tool which will overcome the above mentioned drawback.

It is a further object of this invention to provide an explosively actuated impact tool which can easily and instantaneously be put into operation.

It is a further object of this invention to provide an explosively actuated impact tool in which automatically in response to the lifting off of the impact tool from the object to be worked, the drive of the piston will be interrupted and the piston will be retained in its dead center position adjacent to the work tool carried by the impact tool.

It is also an object of this invention to provide an improved lubricating system for the new impact tool of the invention as set forth above.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

Fig. l-is a longitudinal section through an impact tool according to the invention comprising mechanicalmeans for arresting the free-piston in its lower dead center position.

Fig. '2 is a section through a modified impact tool in which gases under pressure are employed for causing the piston to effect its return stroke.

Fig. 3 illustrates a detail of the tool shown in Fig. 2.

Fig. 4 shows a portion of Fig. 3 on a scale larger than the scale of Fig. 3.

Fig. 5 illustrates a modification of a portion of a driving tool according to the invention.

Fig. 6- shows a portion of Fig. 5 on a scale larger than that of Fig. 5.

Fig. 6a is a slight modification of Fig. 6.

Figs. 7 and 81illustrate the tool of Fig. 2 intwo different positions to'Show theactuation of a lubricating pump only when the working or actuating piston has moved beyond its dead working stroke.

General arrangement The impact tool. according to the present invention which carries a' working tool at its lower end is characterized primarily in that when low outer pressure is exerted upon the working tool, those forces which norcenter position of its normal m mally bring about the return stroke of the piston of the impact tool will not effect the return stroke of the piston but instead will retain said piston in or near the dead center position thereof. In other words, when the work tool is lifted off from the object to be worked, the drive for the piston is automatically interrupted and the piston is arrested in or near its dead center position adjacent the work tool.

The means by which the piston is arrested in or near its lower dead center position may be of different type. Expediently the said means should be such that they will be made inoperative by a pressure exerted from the outside through the working tool in axial direction of the latter. Thus, for instance, the piston or its extension, i. e. the piston rod may be acted upon by a return spring and may be surrounded by a roller or ball locking system the rollers or balls of which are depending on the position of the working tool radially pressed inwardly from the outside by means of an axially displaceable sleeve pro vided with a conical surface. More specifically, according to an advantageous embodiment of this arrangement, the rollers or balls are radially movably mounted in a cage or the like which latter surrounds the piston or the piston rod and is connected to the casing of the explosively actuated impact tool. Outside said cage there is provided an axially movable sleeve which has an inner conical surface adapted to act upon said balls or rollers 811d arranged within the path of the working tool.

When the said casing is sub-divided along a transverse plane, it is expedient to clamp the roller or ball cage by means of an annular flange thereof between thetwo casing portions so that the cage cannot be moved in axial direction. In this connection a spring is provided tending to maintain contact between the said sleeve having an inner conical surface and the working tool or an intermediate member engaging said working tool such as a guiding sleeve for said working tool.

Instead of providing means which act against the forces for effecting the return stroke of the piston, in other words instead of employing the above mentioned ball or roller locking system, the arresting means for the piston may also be designed in such a manner that the piston is actuated upon by a valve controlled gas. The said valves are preferably so arranged and designed that they will control the gas supply into the pressure chamber upon the back side of the piston-lower compression chamber--in conformity with the position of the piston. When the impact tool comprises a casing which is sub-divided along a transverse plane into an upper and lower casing section, the said valves are preferably arranged in the upper casing section in such a manner that the stems of the valves are arranged radially inwardly in the path of the piston, While the piston has a tapered section at the end near said valves, said tapered section being adapted to engage and actuate said valve stems. The gas employed for operating the explosively actuated impact tool may also be used as gas for bringing about the return stroke of the piston.

Instead of employing radially displaceable stem equipped valves for controllingthe supply of gases under pressure, also a ring of elastic material with a U-shaped I profile may be provided having its ends inwardly angled.

The invention also comprises a lubricating device for explosively actuated impact tools, especially for such impact tools comprising means which when no outside pressure is exerted upon the working tool will make inefiective or counteract the forces tending to bring about the return stroke of the piston and will arrest the piston in or near its lower dead center position. The lubricating system according to the invention is particularly advantageous in connectionwith such explosively actuated impact tools in. which the piston in its inefiective position occupies a position lower than the normal lower dead center position of the piston. In such an instance the lubricating pump may be so arranged that it can be actuated only when the free-piston has been moved beyond said dead center position. The arrangement may be such that the free-piston acts upon the piston of the lubricating pump. However, it is also possible to actuate the piston of the lubricating pump by the pressure gas or by the working tool such as a chisel.

Structural arrangement Referring now to the drawing in detail and Fig. 1 thereof in particular, the explosively operable impact tool shown therein comprises a casing forming a cylinder in which a free-piston 11 is reciprocably arranged. The piston 11 has connected thereto a piston rod 12 which in its turn is guided in a bushing 13. A spring 14 has one end thereof resting against the bushing 13, whereas the other end of spring l l'engages the free-piston 11. As will be clear from the drawing, the spring 14 surrounds the piston rod 12. The cylinder 19 is provided with an exhaust 101 and is furthermore provided with an inlet opening 10a communicating with a carburetor 192 (shown diagrammatically only). The exhaust 1G1 and the intake passage 10a communicate, in a manner known per se, with the explosion chamber 163 of the cylinder 10.

The lower end of the cylinder 11) is provided with an annular flange 104 which is connected in any convenient manner for instance by bolts with an annular flange 151 pertaining to the lower casing portion 15. Both casing portions 10 and 15 are provided with annular steps 105 and 152 respectively which are located opposite each other. Confined by these steps and arranged therein are a flange 134 of the guiding bushing 13 and a flange 161 of a roller or ball cage 16. The said two flanges 134 and 161 are clamped between the casing portions 10 and 15 when said casing portions are connected to each other for instance by bolts.

The roller cage 16 is provided with balls 17 which are supported by said cage 16 in such a manner that they are movable in radial direction within certain limits. A sleeve 18 having its inner surface 181 cone-shaped surrounds the said balls in such a manner that when the sleeve 18 moves downwardly, the balls 17 will from a certain position on of sleeve 18 be pressed inwardly against the piston rod 12. The upper end surface of the sleeve 18 is engaged by one end of a spring 19 the other end of which rests against the flange 161 of the ball cage 16. The sleeve 18 itself rests upon a flange 201 of a longitudinally displaceable guiding bushing 20 of the work tool 21 and is adapted to be displaced axially by the tool 21 against the thrust of the spring 19.

The Work tool 21 which may, for instance, be a chisel has a collar 211 which limits the inward movement of the tool into the casing portion 15. A further collar 212 likewise forming part of the tool 21 is arranged and designed that when the work tool is under load, the collar 212 will rest against the guiding bushing as for the tool stem 21:: so as to displace said guiding bushing 20 upwardly. Instead of the collar 212, also one or a plurality of noses or the like may be provided.

During the normal working operation, and more specifically at the instant when the piston rod 12 hits the tool stem 21a, the latter occupies the position shown on the right-hand side of Fig. l. The collar 212 still presses the guiding bushing 20 and the sleeve 18 inwardly so that the balls 17 cannot arrest the piston rod 12. When, however, the impact tool is lifted so that no counter pressure is exerted any longer upon the workingtool 21, the toolstern 21a will move into the position shown on the left-hand side of Fig. l. The working tool 21 sinks downwardly when the impact tool is lifted. The piston 11 is thrown outwardly beyond its working dead center position. The

sleeve 18 will then be able to yield to the pressure exerted by spring 19 and will likewise be displaced downwardly.

Due to the conical surface 181 of the sleeve 13, the balls 17 will now be moved radially inwardly so that they will rest against the piston rod 12 under pressure and will clamp fast said piston rod 12. When the impact tool is again to be put into operation, the work tool 21 is pressed against the material to be worked whereby the collar 212 presses the bushing 20 inwardly. As a result thereof, the sleeve 18 is displaced against the thrust of spring 19 so that the inner conical surface 181 will be outside the range of the balls 17 and, therefore, the balls will again be located loosely in their cage, thereby releasing the piston rod. The spring 14 will then throw the free-piston 11 upwardly so that the gas in the chamber 103 will be compressed and ignited. The piston 11 will beat against the work tool 21 at each ignition.

With explosively operated impact tools in which the piston return stroke is efifected by compressed gases such as compressed air or fuel gas under pressure, it is possible in a manner similar to that of Fig. l to arrest the piston in its bottom dead center position against the power tending to effect the return stroke. In other words, the piston can be arrested against the power tending to effect its return stroke. However, with explosively actuated impact tools in which the piston return stroke is effected by gases under pressure, it is preferable to make the said returning power of the gases under pressure ineffective when the explosively actuated-impact tool is put away. To this end, the supply of effective gases under pressure below the piston is interrupted. The arresting device for the piston will then have to overcome the piston weight only but not the returning force.

Such embodiments are diagrammatically shown in Figs. 2 to 5. The impact tools according to Figs. 2 and 3 likewise comprise two casing portions 22 and 23. The cylinder chamber 220 serves as upper compression and explosion chamber. The free-piston 24 is displaceably mounted in the cylinder chamber 220, said piston being arranged to act upon the work tool 21 through the intervention of a striker 25.

At the piston back there is provided a lower pressure chamber 27 which chamber is surrounded by an annular passage 26 in casing portion 22 for delivering gas under pressure. The upper portion 22 of the casing, and the passage 26-communicate with each other through passages 260 when the piston occupies its upper position. The lower casing portion 23 is provided with a collar surrounding the chamber 27. This collar is provided with bores 230 registering with said passages 26%, while in each of said bores 230 there is displaceably mounted a valve body 29 acted upon by a spring 28. These valves 29 have a collar 290 which is adapted to close off the respective passages 260. Such closing off of the respective passages 260 will occur when valve stems extending into the pressure chamber 27 are pushed out of the piston path against the thrust of spring 28 by the piston 24 which hits against the work tool. With such explosively actuated impact tools in which the gas under pressure is simultaneously fuel gas, passages 30 extend from the lower pressure chamber 27 to the valves 31 which if desired are each actuated by a spring 32. Nozzles 33 communicate with the gas valves 31, said nozzles extending into the scavenging channel 34. The cone-shaped surface 310 of the valve 31 closes the valves 31 when the piston 24 is in its upper position. The impact tool according to Fig. 2 operates in the following manner:

First the work tool 21 which prior to the .working operation occupies the position shown on the left-hand side of Fig. 2 is placed against the object to be worked whereby the free-piston 24 is moved upwardly through the intervention of the striker 25. As soon as during this movement, the cone-shaped piston portion 240 has passed the valves 29, the valve stems thereof are pressed radially inwardly by means of the springs 28. As a result thereof, gas under pressure passes from the annular passage 26 connected to a supply of gas under pressure,

into the lower compression chamber 27 thereby pushing the piston 24 upwardly. The gas employed for this purpose may be air under pressure but, similar to the arrangement of Fig. 2, also fuel gas may be used for this purpose. The passage 26 may be connected to a conduit conveying gas under pressure or may be connected to a bottled gas cylinder of any known type. The gas is passed through passages 30 and open valves 31 through nozzles 33 from where the gas passes into the scavenging channels 34. The gas draws fresh air along and mixes with the same in the cylinder chamber 221 into which it passes according to the cross flow scavenging principle. The gases which possibly remained in the cylinder chamber 229 from the previous explosion are thus pressed through the openings 211 into the exhaust. When the piston 24 has moved beyond the valves 31, said valves close so that no further gas can pass through the nozzles 33. By meansof the upwardly thrown piston 24, the gas in the cylinder 220 is compressed to such an extent that it will self-ignite.

The now occurring explosion throws the piston 24 downwardly. At the instant at which the piston 24 frees the slots 211 leading to the exhaust, the exhaust gases pass through said slots. The downwardly pressed piston 24-now strikes through the striker 25 against the working tool 21 placed on the material to be worked. During the downward movement of the piston 24, the valves 31 are again opened by the piston so that the nozzles 33 will again allow gas to pass therethrough. Also when the Work tool 21 is placed upon the material to be worked,

the piston is moved to a minor extent beyond the position shown on the right-hand side of Fig. 2. However, the stems of the valves 25 are not moved into closing position but the working cycle will be repeated until the impact tool is lifted off from the work piece so that no pressure will be exerted any longer upon the working tool 21.

If the impact tool is lifted off from the work piece, the piston does not engage any resistance any longer and flies beyond its working dead center position thereby moving the stems of valves 29 into the closing position shown on the left-hand side of Fig. 2. Consequently the flow of gas into the chamber 27 is cut off. However, the gas which is in. the chamber 27' is first compressed and will then escape through the bore 35, overflow valve 36 (Fig. 3.) and bore 37 into the annular chamber 26. By correspondingly dimensioning the parts 35 and 37, the cushioning of the free-piston 24 can be controlled. The small quantity of gas remaining in the lower pressure chamber 27 is insuflicient to press back the piston 24. This is due to the fact that already following the least upward movement of the piston, a low pressure is created in chamber 27 and the stems of the valves 29, 31 will create a friction impeding the movement of the piston.

These conditions also prevent the impact tool from accidentally being put into operation as a result of an accidental slight axial pressure exerted upon the work tool 21. If, however, an axial pressure is exerted upon the impact tool by placing the same upon the surface to be worked, as this is the case in the working position of theimpact tool, the piston 24 is pushed upwardly. After the valves 29 have been released, the gas under pressure passes into the chamber 27 and brings about the further movement of piston 24. The stroke performed by the piston in this connection and the time during which the gases for returning the piston act upon the latter during the starting stroke are, as will be obvious from the' drawing, greater than during the normal working stroke so that during the starting and first compression stroke a particularly violent compression occurs in the cylinder 22%.

If during the first starting attempt no ignition should occur, the free pi'ston 24 would after a few gradually decreasing short reciprocating strokes be arrested in its 6 upper dead center position by the preloaded return pressure gases. In this instance, by abutment of the impact tool, the piston 24 can be pushed downwardly without tool and against the return force to such an extent that the shut-off valves will be brought into'a corresponding position. For purposes of making the returning gas forces ineffective when the starting attempt fails, a discharge valve 38 (Fig. 2) is provided. After the feeding line from the air pressure container has been closed off, the discharge valve 38 can be opened by exerting pressure upon its pin 38a so that the preloaded pressure gas which arrests the piston in its upper dead center point can escape into the open through the bore 39.

Whereas explosively actuated impact tools operated with liquid fuel such as gasoline are lubricated like ordinary auto two-stroke engines by admixing lubricant to the fuel, a separate lubricating device, for instance a lubricating pump is necessary with explosively actuated impact tools which are operated by gas as fuel. In order to be able to control the quantity of lubricant, it is not necessary to put the pump into operation with each working stroke of the piston. It is rather possible so to arrange the pump in the fuel driving arrangement that the pump is to be operated merely when putting the impact tool away or again putting the impact tool into operation. Such a pump is diagrammatically illustrated in Figs. 3, 4, 7, and 8.

According to Fig. 3, there is provided a chamber 40 which may be filled with oil. This chamber is arranged in the lower casing portion 15 or 23 respectively. A bore 41 leadsfrom the chamber 49 into a cylindrical bore 42- in which a piston in the .form of a rod 43 is axially movable'and guided. This piston rod 43 is acted upon by a spring 44 tending to press the piston 43 upwardly into Fig. 4 position. To this end, the piston 43 is provided with a collar 430 against which rests the spring 44. The cylindrical bore 42 is closed ofi by a check valve 46. This check valve 46 seals the cylindrical chamber 42 with regard to the chamber'47 from where bores 48 (Fig. 4) lead to the individual lubricating points of the impact tool. During the normal working operation, the piston 43 takes up a position in which the collar 430 rests against the closure plate 45 (Fig. 7) of the piston impact tool is put away, the piston 24 presses upon the piston 43 of the lubricating pump and presses the oil drawn in through bore 41 during the upward stroke into the chamber 4'7 through the check valve 46 from where the lubricant is passed to all lubricating stations. When the impact tool is being placed into operation, the piston withdraws lubricating oil due to the pressure of its spring 44-, and the said lubricating oil is pressed into the lubricating conduits during the next adjustment.

The impact tool shown in Figs. 5 and 6 diifers from that of Figs. 2 and 4 merely in that instead of the valves 29 there is employed a ring 49 of elastic material. The said ring has a U-s-haped profile with slant inwardly directed lips 4% as shown in Figs. 5 and 6. This elastic ring rests in a sealing manner against the piston 24 when the latter is moved beyond its working dead center position. The pressure gas which remained in chamber 27 can escape from this chamber since due. to the now occurring compression of the gas, the gas will temporarily lifit oil the lip 49d. The pressure gas in the chamber 2.7 can thus pass into the chamber 26. This situation is shown in Fig. 6. on an enlarged scale.

Fig. 6a shows a slight modification of Fig. 6-inasmuch as thering 49 of Fig. 6 has been replacedby two rubber rings 49a. 7 v

It is, of course, understood that the present, invention is, by no means, limited to-the particular constructions shown in the drawings but also comprises any modificas tions within the scope of the appended claims.

What we claim is: a

1. An explosively operable impact tool, which comprises in combination: a casing including a cylinder, piston means freely reciprocably mounted in said cylinder, said cylinder being provided with inlet and outlet means for admitting driving gas into and exhausting combustion gas from said cylinder, means associated with said casing for slidably receiving the stem of a work tool to be actuated by said impact tool, said piston means being arranged to convey actuating power upon said work tool, retracting means arranged normally to return said piston means to its starting position following each working stroke of said piston means, and frictional retaining means operable automatically in response to the lack of pressure from the outside of said impact tool in axial direction of and upon said stem to frictionally engage said piston means to thereby prevent said piston means from performing its return stroke.

2. An explosively operable impact tool, which comprises in combination: a casing including a cylinder, piston means freely reciprocably mounted in said cylinder, said cylinder being provided with inlet and outlet means for admitting driving gas into and exhausting combustion gas from said cylinder, rod means reciprocably mounted within said casing in axial direction thereof and operable by said piston means, means associated with said casing for slidably receiving the stem of a work tool to be actuated by said impact tool, said rod rod means being arranged for cooperation with said stem and being mov-.

able inwardly in response to a certain pressure acting upon said stem from the outside of said impact tool, returning means arranged within said casing and adapted normally to convey retracting power to said piston means for returning the same to its starting position following each working stroke of said piston, and clamping means operable automatically in response to the lack of pressure from the outside of said impact tool in axial direction of and upon said stem to prevent said piston from eifecting its return stroke, said clamping means automatically moving into ineffective position in response to the inward movement of said rod means by said certain pressure acting upon said stem from the outside of said impact tool.

3. An explosively operable impact tool, which comprises in combination: a casing including a. cylinder, piston means freely reciprocably mounted in-said cylinder, said cylinder being provided with inlet and outlet means for admitting driving gas into and exhausting combustion gas from said cylinder, means associated with said ca-sing for slidably receiving the stem of a Work tool to be actuated by said impact tool, said piston being arranged to convey actuating power upon said work tool, retracting means continuously urging said piston to return to its starting position, and locking means including a reciprocable member and operable automatically in response to the lack of pressure from the outside of said impact tool in axial direction of and upon said stem to arrest said piston at least near its lower dead center position, said reciprocable member being responsive to outside pressure upon and in axial direction of said stem for preventing said locking means from becoming effective.

4. An explosively operable impact tool, which comprises in combination: a casing including a cylinder, piston means freely reciprocably mounted in said cylinder and provided with extension means in axial direction of said piston means, said cylinder being provided with inlet and outlet means for admitting driving gas into and exhausting combustion gas from said cylinder, means associated with said casing for slidably receiving the stem of a work tool to be actuated by said impact tool, said extension means being arranged for cooperation with said stern and being movable inwardly in response to a certain pressure acting upon said stem from the outside of said impact tool in axial direction of said stem, spring means arranged within said casing and normally conveying retracting power to said piston means for returning the same to its starting position following each working stroke of said piston means, and locking means including rotatable bodies adapted in response to the lack of a certain pressure from the outside of said impact tool in axial direction of and upon said stem to cause said rotatable bodies to move in radial direction with regard to said impact tool into engagement with said extension means to thereby lock said piston means at least near its lower dead center position.

5. An explosively operable impact tool, which comprises in combination: a casing including a cylinder, piston means freely reciprocably mounted in said cylinder and provided with extension means in axial direction of said piston means, said cylinder being provided with inlet and outlet means for admitting driving gas into and exhausting combustion gas from said cylinder, means associated with said casing for slidably receiving the stem of a work tool to be actuated by said impact tool, said extension means being arranged for cooperation with said stem and being movable inwardly in response to a certain pressure acting upon said stem from the outside of said impact tool in axial direction of said stem, spring means arranged within said casing and normally conveying retracting power to said piston means for returning the same to its starting position following each working stroke of said piston means, and locking means responsive to the lack of a certain axial pressure upon said stem from the outside of said impact tool for locking said piston means at least near its lower dead center position against the thrust of said spring means, said locking means including a cage surrounding said extension means and carrying rotatable bodies movable in axial direction to and into engagement with said extension means and also including a sleeve surrounding said cage and provided with an inner cone-shaped surface section adapted in response to a certain movement of said sleeve to cause said rotatable bodies frictionally to engage said extension means.

6. An explosively operable impact tool, which comprises in combination: a casing comprising an upper section being flanged at one end and forming a cylinder at the other end and also comprising a lower section being flanged at its upper end and having a bore through its lower end for receiving the stem of a work tool to be actuated by said impact tool, piston means freely reciprocably mounted in said cylinder and provided with extension means in axial direction of said piston means, said cylinder being provided with inlet and outlet means for admitting driving gas into and exhausting combustion gas from said cylinder, said extension means being arranged for cooperation with said stem and being movable inwardly in response to a certain pressure acting upon said stem from the outside of said impact tool in axial direction of said stem, retracting means arranged within said casing and normally conveying retracting power to said piston means for returning the same to its starting position following each working stroke of said piston means, and locking means responsive to the lack of a certain axial pressure upon said stem from the outside of said impact tool for locking said piston means at least near its lower dead center position against the thrust of said retracting means, said locking means including a cage surrounding said extension means and carrying rotatable bodies movable in axial direction to and into engagement with said extension means and also including a sleeve surrounding said cage and provided with an inner coneshaped surface section adapted in response to a certain movement of said sleeve to cause said rotatable bodies frictionally to engage said extension means, said cage being provided with a flange clamped between said upper and said lower casing section.

7. An explosively operable impact tool according to claim 6, which includes spring means interposed between said cage flange and one end of said sleeve for continuously urging said sleeve into position for moving said rotatable bodies radiallyinwardly, said stern being arranged to exert axial pressure upon the other end of said and arranged slidably to receive therein the stem of a work tool to be actuated by saidimpact tool, said piston means being arranged to convey actuating power upon said stem and thereby upon sai'd work tool, said stem bea ing provided with means to engage said sleeve means for m'ovlng'the same inwardly in response to an inward movement of said stem, retracting means arranged normally to return said piston means to its starting position following each working stroke of said piston means, extension means connected to said piston means and arranged to act upon said stern, stationarily arranged cage means surrounding said extension means and provided with a plurality of axially movable locking means, bushing meanstmovable from an inelfective position into a locking position for causing said locking means to arrest said extension means, thereby arresting said piston means, and yielding means continuously urging said bushing means to move into locking position, said bushing means being movable inwardly away from its locking position by said sleeve means. 7

9. An explosively operable impact tool, which comprises in combination: a casing including a cylinder, piston means freely reciprocably mounted in said cylinder and having an advancing side and a retraction side, said cylinder being provided with inlet and outlet means for admitting driving gas to said advancing side and exhausting combustion gas from said cylinder, means associated with said casing for slidably receiving the stem of a work tool to be actuated by said impact tool, said piston means being arranged to convey'actuating power upon said work tool, conduit means arranged to convey gases under pressure to the retraction side of said piston means for returning said piston means to its starting position, valve means associated with said conduit means for controlling the supply of gases under pressure to said retraction side in response to a certain position of said piston means, and additional means operable automatically in response to the lack of pressure from the outside of said impact tool in axial direction of and upon said stem to prevent said piston means from performing its return stroke.

10; An explosively operable impact tool according to claim 9, in which said valve means comprise stem means extending radially inwardly with regard to said casing and into the path of said piston means, that end of said 'piston means which is adjacent said retraction side thereof being tapered for cooperation with said valve stem means.

11. An explosively operable impact tool according to claim 9, in which said conduit means are arranged to convey fuel gases to said retraction side.

12. An explosively operable impact tool, which comprises in combination: a casing including a cylinder, piston means freely reciprocably mounted in said cylinder and having an advancing side and a retraction side, said cylinder being provided with inlet and outlet means for admitting driving gas to said advancing side and exhausting combustion gas from said cylinder, means associated with said casing for slidably receiving the stem of a work tool to be actuated by said impact tool, said piston means being arranged to convey actuating power upon said work tool, conduit means arranged to convey gases under pressure to the retraction side of said piston means for returning said piston means to its starting position, valve means associated with said conduit means, for controlling the supply of gases under pressure to said retraction side in response to a certain position of said piston means,

said valve means comprising an annular member of elastic material having a U-shaped profile with inwardly directed lips for engagement with said piston means, and additional means operable automatically in response to the lack of pressure from the outside of said impact tool in axial direction of and upon said stem to prevent said piston means from performing its return stroke.

13. An explosively operable impact tool which comprises in combination: a casing including a cylinder, piston means freely reciprocably mounted in said cylinder and movable during its normal working stroke from an upper dead center position to a lower dead center position, said cylinder being provided with inlet and outlet means for admitting driving gas into and exhausting combustion gas from said cylinder, means associated with said casing for slidably receiving the stem of a work tool to be actuated by said impact tool, said piston means being arranged to convey actuating power upon said Work tool, retracting means arranged normally to return said piston means from its lower dead center position to its upper dead center position following each working stroke of said piston means, additional means operable automatically in response to the lack of pressure from the outside of said impact tool in axial direction of and upon said stem to allow said piston means to move in the direction toward and beyond said lower dead center position, said additionaltmeans including locking means for locking said piston means at least near said last mentioned position, and lubricating pump means responsive to the movement of said piston means beyond said lower dead center position for effecting lubrication of said impact tool.

14. An explosively operable impact tool which comprises in combination: a casing including a cylinder, piston means freely reciprocably mounted in said cylinder and movable during its normal working stroke from an upper dead center position to a lower dead center position, said cylinder being provided with inlet and outlet means for admitting driving gas into and exhausting combustion gas from said cylinder, means associated with said casing for slidably receiving the stem of a work tool to be actuated by said impact tool, said piston means being arranged to convey actuating power upon said work tool, retracting means arranged normally to return said piston means from its lower dead center position to its upper dead center position following each working stroke of said piston means, additional means operable automatically in response to the lack of pressure from the outside of said impact tool in axial direction of and upon said stem to allow said piston means to move in the direction toward and beyond said lower dead center position, said additional means including locking means for locking said piston means at least near said last mentioned position, and lubricating pump means operable by said piston means beyond said lower dead center position for effecting lubrication of said impact tool.

15. An explosively operable impact tool which comprises in combination: a casing including a cylinder, piston means freely reciprocably mounted in said cylinder and movable during its normal working stroke from an upper dead center position to a lower dead center position, said cylinder being provided with inlet and outlet means for admitting driving gas into and exhausting combustion gas from said cylinder, means associated with said casing for slidably receiving the stem of a work tool to be actuated by said impact tool, said piston means being arranged to convey actuating power upon said Work tool, retracting means in form of compressed gas arranged normally to return said piston means from its lower dead center position to its upper dead center position following each working stroke of said piston means, additional means operable automatically in response to the lack of pressure from the outside of said impact tool in axial direction of and upon said stem to allow said piston means to move in the direction toward and beyond said lower dead center position, said additional means including locking means for locking said piston means at least near said last mentioned position, and lubricating pump means operable by said compressed gas in response to the movement of said piston means beyond said lower dead center position.

16. An explosively operable impact tool which comprises in combination: a casing including a cylinder, piston means freely reciprocably mounted in said cylinder and movable during its normal working stroke from an upper dead center position to a lower dead center position, said cylinder being provided with inlet and outlet means for admitting driving gas into and exhausting combustion gas from said cylinder, means associated with said casing for slidably receiving the stem of a work tool to be actuated by said impact tool, said piston means being arranged to convey actuating power upon said work tool, retracting means arranged normally to return said piston means from its lower dead center position to its upper dead center position following each working stroke of said piston means, additional means operable automatically in response to the lack of pressure from the outside of said impact tool in axial direction of and upon said stem to allow said piston means to move in the direction toward and beyond said lower deadcenter position, said additional means including locking means for locking said piston means at least near said last mentioned position, and lubricating pump means operable by said work tool in response to the movement of said piston means beyond said lower dead center position for eifec'ting lubrication of said impact tool.

References Cited in the file of this patent UNITED STATES PATENTS Rice Sept. 6, 1949

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