US3397617A

US3397617A - Pneumatic percussion machine

Info

Publication number: US3397617A
Application number: US426521A
Authority: US
Inventors: Cast Adolf; Reich Kurt
Original assignee: Karl M Reich Maschinenfabrik GmbH
Current assignee: Karl M Reich Maschinenfabrik GmbH
Priority date: 1964-12-24
Filing date: 1965-01-19
Publication date: 1968-08-20
Anticipated expiration: 1985-08-20
Also published as: FR1421020A; NL6415071A; GB1070051A

Description

Aug. 20, 1968 Filed Jan. 19, 1965 A. CAST ET Al.

PNEUMATIC PERCUSS ION MACHINE 2 Sheets-Sheet 1 Adolf CAST and Kur-1' REICH [gpl/LOM ug. 2o, 1968 A. CAST ET AL 3,397,617

v PNEUMATIC PERCUSSION MACHINE Filed Jan. 19, 1965 2 Sheets-Sheet 2 Inl/enfans.- Aoof CAST and Kurf REICH Aj.- uum ffm heirfforney United States Patent O 3,397,617 PNEUMATIC PERCUSSION MACHINE Adolf Cast, Oberlenningen, Wurttemberg, and' Kurt Reich, Nuertingen, Wurttemberg, Germany, assignors to Karl M. Reich Maschinenfabrik, Nurtingen, Wurttemberg, Germany, a firm of Germany Filed Jan. 19, 1965, Ser. No. 426,521 17 Claims. (Cl. 91-41) ABSTRACT OF THE DISCLOSURE An improved pneumatic percussion machine in which a holding device of rubberlike elastic material is operatively mounted in the machine. The holding device comprises a holding element, which is adapted to resiliently engage a nail-driving piston reciprocally mounted in said machine when the later is in a rest position and to suddenly release said piston with a snap action after a predetermined pneumatic driving force has built up behind said nail-driving piston.

The present invention relates to improvements in pneumatic percussion machines which are employed, for example, for nailing, stapling, punching, ramming, ejecting, or similar purposes. A machine of this type is generally provided with a percussion piston which is movable within a working cylinder from a neutral or rest position to an operative position and then back to its rest position and divides this cylinder into two chambers, one of which serves as a pressure chamber which is connected to a supply of compressed air by means of a main valve which may be opened when desired to exert a yforce upon the piston for propelling the same from its rest position to its operative or striking position, while the second chamber is provided with at least one aperture through which the air may be discharged which is displaced by the piston during its power stroke.

A machine of this type is generally provided at the upper end of the pressure chamber Iwith a suitable device for holding the piston in its rest position. This device from which the piston may be released by the action of the compressed air holds the piston in its rest position until the main valve has been opened and the pressure above the piston has then been built np to such a strength that the piston vvill be propelled from the beginning of its power stroke at the highest possible velocity.

Such holding devices have in the past ybeen designed, for example, in the form of relatively complicated spring mec-hanisms. A mechanism of this type is described, for example, in the U.S. Patent No. 2,786,450. There is also another known type of a holding device for the mentioned purpose in which the holding element consists of a permanent magnet which is installed in the cylinder head and adapted to hold the steel piston in its rest position by its magnetic force.

The known spring mechanisms have the disadvantage that their production is relatively expensive, that in the operation of the machine they are very susceptible to trouble, and that parts thereof are easily broken as a result of the impacts which these machines produce. Permanent magnets are likewise very expensive and can be employed only for holding relatively light pistons which moreover must at least partly consist of steel in order to be held in their rest position by magnetic force.

It is a general object of the present invention to provide an improved pneumatic percussion machine which may be either of a stationary or portable type.

It is another object of the invention to provide a per- "ice cussion machine which may be produced very easily and inexpensively.

A more specific object of the invention consists in providing a greatly improved device for holding the percussion piston in its rest position and for releasing it to carry out a power stroke.

A further object of the invention consists in providing such a holding device of such a construction and such a material that it may be produced very easily `and at a low expense as an element separately from the percussion machine itself and `may be easily installed in the machine and quickly exchanged when necessary.

A Ifurther object of the invention consists in designing such a holding device so that it will always carry out its functions reliably even under severe shocks and impacts.

A further object of the invention is to provide a holding device which comprises a holding element of a rubberlike elastic material ywhich is adapted to interengage resiliently with the percussion piston in its rest position and then to connect this piston resiliently in a substantially xed position to the Working cylinder. This holding element may be made of a highly wear-resistant plastic, for example, of a poly addition product of diisocyanate such as is known commercially under the trademark Vulcollan.

The employment of such a holding element of a rubberlike elastic material has the advantage that, when made of a suitable design, it may form the entire holding device or at least the essential part thereof and may be produced very easily and at a low expense by molding. It is extremely Wear-resistant and capable of carrying out its functions for a long time and may also be easily exchanged when necessary. According to some of the preferred embodiments of the invention, the holding element may either consist of `a simple cup-shaped or mushroomlike part which in asociation with a piston or piston head of an inversely corresponding shape may be connected to or disconnected from the latter with a snap action. It may, however, also be made of a still more simple design in the -form of a sealing ring of a highly wear-resistant rubberlike elastic material which in the rest position of the piston may connect the latter resiliently to the working cylinder by engaging into opposite annular grooves in both parts. When the required pneumatic pressure is exerted upon the piston to carry out a power stroke, this pressure exceeds the holding action of the holding element so that the piston will be suddenly disconnected from the holding element and propelled rapidly away from it. Another very important advantage of employing such a holding element of a rubberlike elastic 4material consists in the fact that this element will be resiliently deformed when the piston is =being connected thereto and disconnected therefrom and that `when it is made of a suitable shape, it may also be resiliently deformed by direct action of the compressed air either in the rest position of the piston or when the piston is being severed from the holding element at the beginning of its power stroke. The holding force ofthe holding device will thus ladapt itself automatically to the particular requirements for the operation of the percussion machine.

Another object of the invention is to design the holding element so `as to serve ladditionally as a resilient valve member of the main valve and/or as a bumper or as a sealing element.

The aforementioned as Well as additional objects, features, and Iadvantages of the present invention will become more clearly apparent from the following detailed description thereof which is to be read with reference to the accompanying drawings, in which 'FIGURE 1 shows a diagrammatically simplified longitudin-al section of a nailing machine with .a cup-shaped holding element;

FIGURE 2 shows a longitudinal section similar to that 3 as shown in FIGURE l ofthe cylinder head of a nailing machine according to a modification of the invention which is provided with a holding element in the form of a slidable sealing ring;

FIGURES 3 and 4 show longitudinal sections similar to the section according to FIGURE 1 of the upper part of a nailing machine according to another modification of the invention in which the holding element has a mushroomlike shape and also forms a resilient valve member of the main valve which is shown in FIGURE 3 in the closed position and in FIGURE 4 in the open position; while FIGURES 5 and 6 show longitudinal sections similar to `those according to FIGURES 3 and 4 of a nailing machine according to a further modification of the invention. i

While the pneumatic percussion machine according to the invention may be of many different designs and be employed for many different purposes, it will be hereafter described by way of example as a pneumatic nailing machine. According to a first embodiment of the invention, as illustrated in FIGURE l, this machine comprises a housing which has la cylindrical part 2 which is closed at its upper end by a removable caplike cylinder head 1 and is provided on one side thereof with a hollow handle 3. This housing part 2 contains an inner Working cylinder 5 in which a percussion piston 4 with a ram rod 14 thereon is slidable, :and an outer cylinder 6 coaxially to and surrounding the cylinder 5 so that an annular chamber 8 is formed between the two cylinders. This chamber 8 communicates through apertures 7 in the lower end of cylinder 5 with the inside of the latter and serves as an air reservoir in which the air is stored which is displaced from cylinder S by the piston 4 during the downward power stroke of the latter and which when this stroke is completed acts upon the l-ower side of the piston and returns the same to its upper position which hereafter is called the rest position. The wall of cylinder 5 is further provided with one or more apertures 9 at such a level that, when piston 4 is in its lowest position at the end of its power stroke, the air reservoir 8 will also be in communication with the pressure chamber of cylinder 5 above the piston 4 and Will thus be additionally supplied with compressed air from this pressure chamber. The extent of the power stroke of piston 4 is limited by its engagement with a resilient buffer 11 which is mounted in the housing 2 at the lower end of cylinder 5. Underneath the parts as above described the housing 2 carries at -one side thereof a magazine 12 in which a plurality of nails 13 are lined up in a row and are slidable in a direction at right angles to the `axis of the ram rod 14 and piston 4 and individually into a nail channel 15 which guides the ram rod 14 during its stroke. Thus, `at each power stroke of piston 4, the ram rod 14 strikes upon a nail 13' in the nail channel 15 and drives the same into a workpiece, not shown.

On its outer end, the handle 3 of the machine carries a connection fitting 17 which permits the chamber 16 within the hande to be connected to a compressed-air line, not shown. Handle 3 fur-ther contains a valve housing 20 which in this particular embodiment of the invention forms a separate element which is tightly secured in coaxial bores in the wall of handle 3 and provided within chamber 16 with the transverse bores through which the compressed air passes from chamber 16 to the inside of the valve housing 2,0. This valve housing 20 contains a valve ball 21 which is normally pressed by a spring 18 upon a valve seat 19 so as to shut off the supply of compressed air to a channel 22 which terminates into an annular chamber 23 between cylinder 6 and the outer Wall of housing 2. This chamber 23, in turn, communicates at its upper end A with the open upper end of the working cylinder 5 and thus with the pressure chamber within this cylinder above the piston 4.

Above its actual piston part 4 which is in sliding engagement with the wall of cylinder 5, piston 4 is provided with a piston head 4" which has a maximum outer diameter slightly smaller than the inner diameter of cylinder 5 so as to permit the compressed air to pass through the bore 9 into the air reservoir 8 when piston 4 reaches the end of its power stroke. This piston head 4 is connected t-o the piston part 4 by a neck portion of a smaller diameter which is formed by an annular recess 24 which, when the piston is in its rest position as shown in FIGURE 1, is located at the point of connection between the annular chamber 23 `and the mouth of the pressure chamber of cylinder 5.

For holding the piston 5 in its rest position, a cup-shaped holding element 26 of a rubberlike elastic material is mounted within the removable cylinder head 1 of housing 2 to which it is firmly but removably secured due t0 its own resilience and shape. The mouth 2.5 of this holding element 26 has a smaller diameter so as to engage into the annular recess '24 when the piston head 4'l enters into the cup-shaped holding element 26 and then to grip the piston resiliently and hold it in its rest position in which the upper end of the piston part 4 is located near the upper end of cylinder 5.

The wall of the holding element 26 may be circular and closed so that, when the air pressure first acts upon the piston part 4 and starts toy withdraw the piston head 4 `from the holding element 26, a vacuum will be formed in the latter which increases until it is suddenly released and replaced by compressed air when the piston head is sufiiciently withdrawn from the holding element. The piston head is therefore blown out of the holding element with a considerable force so that the actual power stroke of the piston begins at a very high speed.

If, however, `such a vacuum increases the holding force of the holding element 26 too much, the wall of the latter may be provided with` a slot or slots 27, as shown in FIG- URE 1, through which the compressed air may pass from the annular chamber 23 to the space within the holding element above the piston head 4 and act upon the upper surface of lthe latter.

For opening the main valve which is formed by the valve ball 21 in the valve housing 20, a pin 29 which has a continuous axial bore 31 is lslidably mounted in its axial direction within the lower end of the valve housing and engages Iwith its lower end upon a trigger 32. When this trigger is in its released position as shown, the axial bore 31 in pin 29 connects the annular chamber 23 and thus also the pressure chamber within the working cylinder 5 with the outer air.

The manner of operation of the nailing machine according to FIGURE l is as follows:

When the trigger 32 is actuated, pin 29 engages against the valve ball 21 and lifts the same off its seat 19, so that the axial bore 31 in pin 29 is closed by the valve ball 21 and the compressed air passes from chamber 16 through the channel 22 and the annular chamber 23 into the upper end of the working cylinder 5. If the holding element is provided with slots 27, the compressed air also passes through these slots into the space within the holding element above the piston he'ad 4". As soon as the pressure has reached a certain strength, piston 4 overcomes the resilient gripping force of the cup-shaped holding element 26 and is propelled out of the latter so that the end of the ram rod 14 strikes upon the head of the nail 13 in the nail channel 15 and then drives the nail into a workpiece. During this power stroke `of piston 4, the air which is displaced by it in the cylinder 5 is pumped through the bores 7 'and 9 into the air reservoir 8 in which it is compressed and stored. As soon as piston 4 reaches its lowest position, additional compressed air also passes from the pressure chamber in cylinder 5 past the piston head 4 and through the annular recess 24 and bore 9 into the air reservoir 8. When the trigger 32 is then released, valve ball 21 is pressed by the spring 18 upon its seat 19 so that the further supply of compressed air is shut off from chamber 23. At the same time, the axial bore 31 in pin 29 connects the pressure chamber of cylinder 5 through the annular chamber 23 and channel 22 with the outer air so that the compressed air which was stored in the air reservoir 8 will then propel the piston 4 upwardly until the piston head 4" engages into the cup-shaped holding element 26 and is gripped therein by the inwardly projecting mouth 25. The upper wall of t-he holding element 26 also serves as a buffer to limit the upward movement of piston 4.

FIGURE 2 illustrates a part of a pneumatic nailing machine according to a modication of the invention which differs from the nailing machine according to FIG- URE 1 merely `by the particular construction of its holding element. In order to avoid unnecessary repetition of the previous description, all those parts the functions of which are similar to corresponding parts in FIGURE 1 are indicated in FIGURE 2 by reference numerals which are increased by 100 over those applied in FIGURE l. The holding element according to FIGURE 2 consists of a locking ring 126 of a rubberlike elastic material with high wear-resistant properties whic-h is inserted into an annular groove 124 in piston 104. The upper end of the working cylinder 105 engages into the cap-shaped cylinder head 101 which carries on the inside of its upper wall a buffer 133 which limits the return stroke of the piston 104. When piston 104 is in its retracted or rest position, it engages upon the buffer 133 and its annular groove 124 is then located near the upper end of the cylinder 105 in a position opposite to an annular groove 134 which is provided in the inner wall surface of cylinder 105. Locking ring 126 when not compressed has a larger outer diameter than the piston 1.04 so that, when the latter is in its rest position, ring 126 engages` into the annular groove 124 in piston 104 and also into the annular groove 134 in cylinder 105 and thereby locks the piston 104 to the cylinder 105. The annular groove 124 in piston 104 is, however, made of such a depth that the locking ring 126 will be fully pressed into it against its elastic force when the piston is propelled downwardly. During the power and return strokes of piston 104, locking ring 126 slides along the wall of cylinder 105 and acts as a piston ring.

When in the operation of the nailing machine the cornpressed air passes through the annular chamber 123 into the cylinder head 101, it presses upon the upper end of piston 104 and, When t-he air pressure has reached a sufficient strength, the locking ring 126 is compressed into the annular groove 134 so that the piston 104 is unlocked from the upper end of cylinder 105 and will then be suddenly propelled downwardly by the compressed air.

FIGURES 3 and 4 likewise illustrate only those parts of a pneumatic nailing machine according t-o a further modification of the invention which differ from the machine as illustrated in FIGURE l. Therefore, in order to avoid repetition, all those parts which are equal or similar to corresponding parts as described with reference to FIGURE l are also indicated in FIGURES 3 and 4 by reference numerals which are increased by 200 over those applied in FIGURE 1. The elastic holding element 226 of this embodiment of the invention has a mushroomlike shape with an outwardly bulging head 225 which engages in a manner similar to a snap button into the open upper end of a cup-shaped piston 204 which is provided with an inwardly projecting bead or rim 235. The upper end of the holding element 226 forms an outwardly projecting ange 236 which is secured Within a recess in a control piston 237 which is slidable in the axial direction within the upper end of the cylindrical housing 202. The lower annular end surface 238 of this control piston 237, which surrounds the flange 236 on the holding element 226 and faces the pressure chamber of the working cylinder 205, has a smaller outer diameter than the upper end surface 239. Flange 236 on the holding element 226 has an outer diameter larger than the diameter of the upper edge 241 of the Working cylinder 205 and forms a valve disk which is adapted to engage upon the edge 241 of cylinder 205 forming the associated valve seat so as to shut off the pressure chamber of cylinder 205 from the annular chamber 223 which is connected ito the air-pressure supply line 216.

The holding element 226 has an axial bore 242, the upper end of which will be closed by a pin 243 mounted on the cylinder head 201 when the control piston 237 is in its highest position, as shown in FIGURE 4, in which it engages upon a buffer 244. The axial bore 242 communicates through radial bores 245 in the holding element 226 with the pressure chamber of the working cylinder 205. For permitting the effective length of pin 243 from the upper wall of the cylinder head 201 to be adjusted, the upper end of this pin is provided with a screw thread 246 and is screwed into a tapped bore in the upper wall of the cylinder head 201 on which it may be locked by a check nut 247. Pin 243 passes through a bore 248 in the control piston 237. The lower part 249 of this bore 248 has a slightly larger diameter than the upper part so that an annular gap 251 is formed which communicates with the outer atmosphere through radial bores 252 in the control piston 237 and the annular space 252 between the upper end of the housing 202 and the lower side of the enlarged part of the control piston 237 and then through vents 253 in the wall of the cylinder head 201. Therefore, when the valve which is formed by the control piston 237 and the flange 236 of the holding element 226 is in the closed position as shown in FIGURE 3, the pressure chamber of cylinder 205 communicates with the outer air through the

bores

245, 242, 251, 252, the annular space 252 and bores 253. The space 240` in the cylinder head 201 above the enlarged part of the control piston 237 is connected by a conduit 254 either with the air-pressure supply line 216 through a channel 257 or with the outside air through a vent 255. This depends upon whether a Valve ball 256 in a valve chamber 256 is in the position as shown in FIGURE 3 in which the compressed air passing from the supply line 216 through the channel 257 into the valve chamber 256 presses this ball upon its lower valve seat which forms the mouth of a bore 258 and thereby closes this bore which leads through the vent 255 to the outside, or whether by the actuation of the trigger 232 this valve ball 256 is moved to the position as shown in FIG- URE 4 in which by the actuation of trigger 232 it is lifted by a pin 229 off its lower valve seat and pressed against its upper valve seat, i.e. the mouth of the connecting channel 257, so that this channel leading to the pressure line 216 is closed, While the bore 258 and vent 255 are open to the outside.

The manner of operation of the nailing machine as illustrated in FIGURES 3 and 4 is therefore as follows:

In its rest position as shown in FIGURE 3, the control piston 237 which together with the elastic flange 236 forms the valve disk of the main valve is forced downwardly by the compressed air acting in chamber 240 upon the larger upper end surface 239 so that the elastic flange 236 is pressed upon the upper edge 241 of the working cylinder 205 which forms the valve seat of the main valve. This valve is therefore tightly closed and no compressed air can enter from the annular chamber 223 into the working cylinder 205. When the control piston 237 is in this position, the head 225 of the holding element 226 engages into the cup-shaped piston 204 and maintains the latter in its rest position. If the trigger 232 is then actuated, valve ball 256 is pressed in valve chamber 256 against the upper valve seat which forms the mouth of the connecting channel 257 so that the cornpressed air can no longer enter from the supply line 216 into the conduit 254, but the latter is instead connected through the

bores

258 and 255 with the outer air. Thus, only the lower annular end surface 238 of the control piston 237 is then acted upon by compressed -air so that the control piston 237 together with the holding element 226 will be lifted off the valve seat at the upper edge 241 of cylinder 205 to the position as shown in FIGURE 4.

During this upward movement of the holding element 226, pin 243 enters into the bore 242 of the holding element and thereby shuts oit this bore from the annular gap 251 which is connected through the bores 252, the annular space 252 and bores 253 with ythe outer air. The compressed air can then pass from the supply line 216 through the annular chamber 223 into the pressure charnber of the cylinder 205 and act upon the upper parts of piston 204 and it will also pass through the

bores

245 and 242 in the holding element 226 and act upon the bottom wall of the piston. As soon as the pressure upon the piston 204 has reached a certain strength, the piston is propelled of the holding element 226 and carries out a rapid power stroke. When the trigger 232 is released at the end of this stroke, the valve ball 256 is pressed by the compressed air back upon its lower seat in valve chamber 256, as shown in FIGURE 3, so that the conduit 254 is no longer connected through the

bores

258 and 255 with the outer air but through the channel 257 with the air supply line 216. The air pressure in chamber 240 then acts upon the large upper surface 239 of the control piston 237 and moves this piston to the position as shown in FIGURE 3, in which the main valve is closed. Since by this movement the holding element 226 is lowered so far that pin 243 is removed from the bore 242, the pressure chamber of the working cylinder 205 will then be connected through the

bores

245 and 242, the annular gap 251, and the

bores

252 and 253 with the outer air. Piston 264 is then returned to its rest position in the same manner as described with reference to FIGURE l in which it is telescoped over the head 225 of the holding element and maintained by its inner bead 235 in its rest position. The extent of the return movement of piston 204 is limited by the engagement of the inner bottom wall of the cup-shaped piston against the lower end of the head 225 of the holding element which then serves as a buffer.

The nailing machine according `to the further modiication of the invention as illustrated in FIGURES and 6 differs from the machine according to FIGURES 3 and 4 merely by the particular vconstruction and shape of the mushroomlike holding element.

The above description therefore applies in general also to the embodiment of lthe invention as shown in FIG-

URES

5 and 6 in which all those parts which are equal or functionally similar to the corresponding parts in FIG-

URES

3 and 4 are indicated by reference numerals which are increased by 100 over those applied in FIGURES 3 and 4.

The mushroomlike holding element 326 is in this case not provided with a continuous bore as in FIGURES 3 and 4, but with a bore 342 which has a lower constricted part 361 and ends into a chamber 362 within the head 325 of the holding element. This chamber 362 may at all times communicate with the outer air through an axial bore 363 in pin 343 and its extension 363', as indicated in FIGURE 5 in dot-and-dash lines, or chamber 362 may be connected through the axial bore 363 and radial bores 365 with the chamber 340 in the cylinder head 301 between the upper end wall 339 of the control piston 337 and the upper wall of the cylinder head. The central aperture in the butter 344 is for this purpose made slightly larger than required for the insertion of the pin 343 so as to form an annular gap 364 into which the radial bores 365 terminate which are connected with the upper end of the axial bore 363 in the pin 343. For the same purpose, the lower side of the buffer 344 is provided with recesses 367 which extend lfrom the wall of its central aperture to its outer wall. Pin 343 has on its lower end an extension 366 of a smaller diameter which extends in any position of the control piston 337 into the narrower part 361 of bore 342 and engages with the wall of this part.

The manner of operation of the nailing machine according to FIGURES 5 and 6 is as follows:

In the rest position of the machine as shown in FIG- URE 5, in which the chamber 340 between the upper end wall 339 of the control piston 337 and the upper wall of the cylinder head 301 communicates through the conduit 354 with the compressed-air supply line, the compressed air passes through the

bores

365 and 363 into the chamber 362 in the head of the holding element and expands `the latter to such an extent that it will be securely locked t-o the inner wall surface of the cup-shaped piston 304. If the trigger of the machine is then actuated in the manner as described with reference `to FIGURES 3 and 4, chamber 340 above the upper end wall 339 of the control piston as well as chamber 362 in the head of the holding element will be connected through the conduit 354 with the outer air. As soon as the control piston 337 then starts to move to the position as shown in FIG- URE 6, in which the compressed air passes through the annular chamber 323 into the pressure chamber of the working cylinder 305, the head 325 of the holding element 326 is compressed t-o the shape as illustrated in FIGURE 6 and is thereby unlocked from the piston 304. The return stroke of the piston and the venting of the pressure chamber of the working cylinder 305 then occur in the same manner as described with reference to the nailing machine according to FIGURES 3 and 4. However, during the return stroke of the piston the chamber 362 within the head 325 of the elastic holding element 326 is again lled with compressed air and expanded so that, when piston 304 rebounds elastically at the end of its return stroke after its inner bottom wall hits against the lower end of the head 325, it will be securely gripped by the side wall of this head. In order to insure that, even though the chamber 362 is under pressure, piston 304 will properly slip over the expanded head 325 of the holding element near the end of the return stroke, the upper side 363 of the inner bead 335 of this piston is made of a conical shape.

Although our invention has been illustrated and described with reference to the preferred embodiments thereof, we wish to have it understood that it is in no way limited to the details of such embodiments but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed our invention, what we claim is:

1. A pneumatic percussion machine comprising a working cylinder, a percussion piston movable in the axial direction within said cylinder so as to carry out a power stroke from a rest position to an operative position and thereafter to carry out a return stroke from said operative position back to said rest position, said piston dividing said cylinder into a pressure Chamber and a second chamber, valve means adapted when in one position to supply compressed air to said pressure chamber so as to act therein upon said piston to carry .out said power stroke and when moved to another position to connect said pressure chamber with the .outer air during said return stroke and in said rest position, a wall portion of said cylinder enclosing said second chamber having at least one aperture for discharging the air from said second chamber which is displaced by said piston during its power stroke, means for returning said piston to said rest position after completing said power stroke, and means for resiliently holding said piston in said rest position comprising a holding element at least partly consisting of a rubberlike elastic material, locking means adapted to interengage resiiiently with said holding element when said piston is in said rest position and then to connect said piston resiliently in a substantially fixed position to said cylinder, one of said last two mentioned means having a projecting portion and said other one of said last two mentioned means having a complementary accommodating portion, by means of which said last two mentioned means interengage each other prior to release of said piston, whereby one lof said last two mentioned means undergoes a movement relative to the other one of said last two mentioned means simultaneously with the release of said piston.

2. A pneumatic percussion machine as defined in claim 1, in which said holding element and said piston form two members, one of said members having a head and a neck of a smaller diameter than said head connecting the same to and projecting from the remainder of said member, the other member being cup-shaped and adapted to receive said head telescopically when said piston is in said rest position, said cup-shaped member having a mouth portion of an inner diameter smaller than the maximum diameter of said head, at least a 4part of one of said members being resiliently deformed when said members are moved telescopically over each other.

3. A pneumatic percussion machine as defined in claim 2, in which said cup-shaped member forms at least a part of said holding element and said head forms at least a part of said piston.

4. A pneumatic percussion machine as defined in claim 2, in which said cup-shaped member forms at least a part of said holding element and said head forms at least a part of said piston, said holding element having. at least one aperture in the side wall thereof for the passage of compressed air to a space within said element above said piston head for propelling said piston head out of said holding element at the beginning of said power stroke and for venting said space when said piston head returns to said rest position in said holding element.

5. A pneumatic percussion machine as defined in claim 2, in which said cup-shaped member forms at least a part of said piston and said head forms at least a part of said holding element.

6. A pneumatic percussion machine as defined in claim 5, in which said head of said holding element forms a hollow chamber, and conduit means connecting said chamber with the outer air.

7. A pneumatic percussion machine as defined in claim 1, in which said holding element is so elastic that, when the compressed air passes into said pressure chamber to act upon said piston in said rest position, said compressed air also acts upon said holding element to deform the same at least sufficiently to facilitate the withdrawal of said piston from said rest position to start said power stroke.

8. A pneumatic percussion machine as defined in claim 2, in which said two members are shaped so as to engage with and disengage from each other with a snap action.

9. A pneumatic percussion machine as defined in claim 2, in which an end surface of said head serves as a bumper adapted to engage momentarily with and then to rebound slightly from the bottom Iwall of said cup-shaped member at the end of said return stroke when said piston moves to its rest position.

10. A pneumatic percussion machine as defined in claim 1, in which said pressure chamber of said cylinder has an open end, said holding element comprising a sealing ring of a wear-resistant material, said locking means being formed by an annular groove in the inner wall surface of said cylinder near said open end and by an annular groove in the outer wall surface of said piston, said sealing ring engaging into both annular grooves and thereby connecting said piston to said cylinder in a substantially fixed position when said piston is in said rest position and being compressed entirely into said groove in said piston and sliding with said piston along the wall of said cylinder during said power and return strokes.

11. A pneumatic percussion machine as defined in claim 1, in which a part of said holding element also forms an elastic valve member of said valve means.

12. A pneumatic percussion machine comprising a working cylinder open at its upper end, a housing rigidly secured to and projecting upwardly from said working cylinder at least from a level slightly below said upper end and forming a second cylinder coaxial to and fully enclosing said working cylinder at least upwardly of said level and having an inner diameter larger than said upper end of said working cylinder, a percussion piston movable in the axial direction within said working cylinder so as t0 carry out a power stroke from a rest position to an operative position and thereafter to carry out a return stroke from said operative position back to said rest position, said piston dividing said working cylinder into a first upper pressure chamber and a lower second chamber, and a first locking member on and projecting upwardly from said piston, a wall portion of said -working cylinder enclosing said second chamber having at least one aperture for discharging the air from said second chamber which is displaced by said piston during its power stroke, means for returning said piston to said rest position after completing said power stroke, means for resiliently holding said piston in said rest position comprising a holding element at least partly being formed of a rubberlike elastic material and comprising a pistonlike valve member movable in the axial direction within said second cylinder and adapted to open and close the upper end of said working cylinder, and a second locking member secured to and projecting downwardly from the lower end -wall of Said Valve member, .one of said locking members having a head and neck of a smaller diameter than said head connecting said head to the remainder of the part carrying said head, the other locking member being cup-shaped and adapted to receive said head telescopically when said piston moves to and is in said rest position, said cup-shaped member having a mouth portion of an inner diameter smaller than the maximum diameter of said head so as to hold said head resiliently within said cup-shaped member in said rest position, said valve member of said holding element dividing said second cylinder into an upper third chamber and a lower fourth chamber, manually actuated valve means adapted when in one position to supply compressed air from a source thereof to said third chamber so as to move said holding element downwardly whereby said valve member closes the upper end of said working cylinder when said piston is in said rest position, said valve means when moved to another position connecting said third chamber with the outer air during said return stroke of said piston, and conduit means directly connecting said fourth chamber to said source of compressed air for lifting said valve member with said holding element off the upper end of said working cylinder so as to pass compressed air into said pressure chamber and thereby to act upon said piston to carry out said power stroke.

13. A pneumatic percussion machine as defined in claim 12, in which the inner diameter of the upper part of said second cylinder is larger than that of its lower part, said pistonlike valve member of said holding element having an upper part of a larger outer diameter than its lower part facing said fourth chamber and the upper end of said working cylinder.

14. A pneumatic percussion machine as defined in claim 12, in which said holding element has a first channel extending in the axial direction thereof, and at least one second channel branching off toward at least one side of said first channel intermediate its ends and leading to the outer air, and a valve pin mounted on the upper end ywall of said housing and extending into the upper part of said first channel and adapted to shut off the connection .of at least a part of said first channel with said second channel when said holding element is lifted off the upper end of said working cylinder.

15. A pneumatic percussion machine as defined in claim 14, further comprising adjusting means for varying the length of said valve pin from said upper end wall of said housing and for thus regulating its valve action.

16. A pneumatic percussion machine as defined in claim 12, in which said neck and head are secured to and project downwardly from said valve member of said holding element and said cup-shaped member is secured to and projects upwardly from said piston, said head forming a hollow chamber adapted to be resiliently compressed and expanded.

17. A pneumatic percussion machine as defined in claim 14, in which said neck and head are secured to and project downwardly from said valve member of said holding element and said cup-shaped member is secured to and projects from said piston, said head containing a fth chamber, said valve pin having a bore connecting said fth chamber with said third chamber for passing compressed air into said fifth chamber so as to expand said head and for venting said fifth chamber so as at least partly to collapse said head.

References Cited UNITED STATES PATENTS Powers et al 173-169 Juilfs 227-130 Dupuy et al. 227-130 Grey et al. 92-30 Bade 92-30 Jance 137--461 Bade 91-399 MARTIN P. SCHWADRON, Primary Examiner.

B. L. ADAMS, Assistant Examiner.