Impact Air Driven Tool

Abstract

An impact air driven tool having a cylinder including a piston member slidable therein and capable of being reciprocated by the action of compressed air. A handle cap unit is mounted on the upper end of said cylinder, and a chisel holding unit including a chisel member slidably supported therein is mounted on the lower end of said cylinder. A plurality of bolts are provided for fastening said cylinder, handle cap unit and chisel holding unit together, and a nut is threaded onto one end of each of said bolts adjacent to said handle cap. A socket member is threaded to the other end of each bolt adjacent to said chisel holding unit and has a contact surface on its outer periphery engageable with a supporting surface formed in a cut-out portion of the chisel holding unit whereby the relative rotation of said socket member with respect to said supporting surface is restricted. A stopper member for each nut has a polygonal opening through which the nut extends, and a collar member covers each nut and is held by a split pin extending through the collar and the nut, so that the stopper members and collars are prevented from disengaging.

Description

THe present invention relates to an impact air driven tool and, more particularly, to an impact hammer having within its cylinder assembly a piston operable by the compressed air for driving a chisel.

It has been well known that, in an impact air driven tool of conventional type, the piston is fiercely reciprocated within the cylinder assembly so as to drive the chisel movably mounted on one end of the cylinder assembly, resulting in generation of a relatively greater vibration. In this instance, the greater vibration will cause various disadvantages such as impairment and/or slackening of fastening members employed in the impact air driven tool, and impairment of the chisel holder provided at a tip portion of the cylinder assembly.

The present invention has been made with a view to eliminating the above-mentioned disadvantages inherent to the conventional impact air driven tool.

Accordingly, an object of the present invention is to provide an improved impact air driven tool wherein provision has been made for prevention of slackening of fastener members connecting various parts of said tool.

Another object of the present invention is to provide an improved impact air driven tool including means for cushioning the vibration generated upon striking of the piston upon the chisel holder.

A further object of the present invention is to facilitate smooth movements of the chisel and the piston by the improvement of a lubricator means disposed between the chisel and a bushing secured to the cylinder assembly of the impact air driven tool.

A still further object of the present invention is to provide improved impact air driven tool wherein the driving force of the piston during the operation of the latter is improved by removing the back pressure.

A still further object of the present invention is to provide an improved impact air driven tool wherein means for avoiding blank shots of said tool has been provided in order to prevent said tool from being impaired.

A still further object of the present invention is to provide means for enabling the impact air driven tool to be operated under water by the improvement of the design of each outlet port of said tool.

It should be noted that the above objects of the present invention can be substantially achieved by the combination and function of various parts constituting the impact air driven tool of the present invention, the details of which will be hereinafter fully described with reference to the attached drawings, in which:

FIG. 1 is a longitudinal elevational view of an impact air driven tool constructed in accordance with the teachings of the present invention, with a portion thereof being broken away,

FIG. 2 is a longitudinal sectional view of the impact air driven tool shown in FIG. 1,

FIG. 3 is a top plan view of the impact air driven tool of the present invention with its bolt and nuts being broken away,

FIG. 4 is a bottom plan view of the impact air driven tool of the present invention showing its chisel in cross-section,

FIG. 5 is a cross-sectional view of the impact air driven tool taken along an upper portion of a bushing for slidably receiving a chisel therethrough,

FIG. 6 is a front cross-sectional view of an air outlet portion of the impact air driven tool,

FIG. 7 is a longitudinal sectional view of the impact air driven tool provided with means for removing the back pressure and means for preventing the blank shots in accordance with the teachings of the present invention, and

FIG. 8 is a longitudinal cross-sectional view of an essential portion of the impact air driven tool shown in FIG. 7, on an enlarged scale.

Referring first to FIG. 1 through FIG. 6 in which one preferred embodiment of the present invention is shown, reference numeral 11 represents a cylinder, 12 represents a handle cap mounted n an upper end portion of said cylinder 11, 13 on a chisel holder, 14 represents a chisel movably supported within said chisel holder 13, and 15 represents a piston slidably received within said cylinder. Reference numeral 16 represents bolts extending through respective holes formed on the four corners of any of said cylinder 11, said cap 12 and said holder 13, each end of said bolts 16 upwardly from cap 12 being received by the corresponding nuts 17.

Reference numeral 18 represents socket members each threaded to the other end of each of said bolts 16. Although in this instance as shown each of said socket members 18 is illustrated in the form of box nut, it may be integrally formed with the bolt 16 as desired. However, it should be noted that the socket members 18 have particular shape. That is to say, as can be understood particularly from FIG. 1 and FIG. 4, a large portion of the outer periphery a of each of said socket members 18 is circular and coaxial with the bolt 16, but the remaining portion thereof has a greater radius of curvature than the large portion of outer periphery a so that it may serve as a contact surface b.

The chisel holder 13 has one-side walled cut-out portions 19 extending from a lower end to an upper end at the four corners thereof through which the respective bolts 16 can be inserted. Each vertical wall of the cut-out portions 19 serves as a supporting surface c, as indicated particularly in FIG. 4, which supporting surface c being inwardly curved in conformity with the outwardly curved contact surface b of each of the socket members 18 and also somewhat tapered toward the upper portion of the chisel holder 13. It will be thus understood that the rotational movement of each socket member 18 can be substantially restricted by the corresponding supporting surface c in tight contact with the contact surface b thereof. More particularly, where the socket member 18 is integrally formed with that end of the bolt 16, no relative rotation of said bolt with respect to the chisel holder 13 takes place. However, if the socket member is in the form of box nut as illustrated in FIG. 1, the bolt must be rigidly threaded to said box nut or socket member to such an extent that the lower extremity thereof engages the depth of the bolt receiving hole of said box nut or socket member.

Referring particularly to FIG. 1 and FIG. 3, reference numeral 20 represents stopper members each made of metal having a sufficient thickness and having polygonal openings 21 capable of receiving the shape of the nut 17 threaded to the other end of the bolt 16. In the instance as illustrated, since each nut 17 is provided with six side flats to give the hexagonal shape, each opening 21 is provided on its inner periphery with 12 V-shaped notches d, of which six V-shaped notches being corresponded to the hexagonal shape of the nut 17 while the remaining six V-shaped notches respectively having exterior angles. Thus, it will be understood that, every time when the nut 17 is rotated at angles of 30.degree., it may engage in the opening 21 of the stopper member 20.

Although, in the instance as shown in FIG. 1 and FIG. 3, a pair of the stopper members 20, each having two openings 21 at the both end portions thereof, are provided for the four nuts 17 and therefore each of said stopper members 20 has the shape of spectacles, it should be understood that any shape may be adapted as desired.

Reference numeral 22 thus collars each made of elastic material such as synthetic rubber and adapted to cover the nut 17 for the purpose as will be mentioned later. This collar 22 has a polygonal inner surfaces in conformity with the outer shape of the nut 17, but the radial dimension of said collar is somewhat smaller than that of the nut 17.

It will be thus understood that, when the collar is to be put on the nut 17, it will radially expand and tightly fasten the nut 17 with its lower extremity engaged against an upper surface of the stopper member 20 thereby to prevent the latter from accidentally detaching. It should be noted that each of said collars 22 is provided at its upper portion with a transverse hole through which a split pin 24 is inserted extending through the corresponding transverse hole formed in an ear portion 23 on an upper portion of each of the nuts 17 so that detachment of the collar 22 can be reliably restricted.

Now referring particularly to FIG. 2, reference numeral 27 represents a cushioning member in the cylindrical form made of elastic material such as polyurethane rubber and disposed within the chisel holder 13 in such a manner as to be supported by a seat member 29 provided at the lower end of the chisel holder 13 in tight engagement with the inner peripheral surface of the latter. This cushioning member 27 is provided on its outer peripheral surface with a plurality of annular grooves 28 of arched cross-section.

In FIG. 2, this seat member 29 is shown as disposed within the chisel holder 13 in engagement with the inner peripheral surface of the latter independently of that portion of the chisel holder. However, it may be integrally formed with that portion of the chisel holder as desired.

The chisel 14 is integrally formed at its intermediate portion with a flange 30 adapted to abut against an upper portion of the annular cushioning member 27 when the chisel 14 is downwardly moved.

The cylinder 11 is formed at its lower end with an enlarged diameter portion 31 as shown in FIG. 2, tightly receiving a bushing 32 through which an upper end portion 33 of the chisel 14 is slidably extended. This bushing 32 is provided on its inner peripheral surface with a plurality of fluid passages 34 in the circumferential direction, all of said fluid passages 34 being communicated one another by vertical fluid passages 35.

This bushing 32 is also provided on its upper end with a groove 36 in the radial direction together with a cut-out portion 37 of suitable length as particularly shown in FIG. 5, said cut-out portion 37 being extended from an outer end of said groove 36 so that a vertical gap 38 is formed between the inner peripheral surface of the enlarged diameter portion 31 and the outer peripheral surface of the bushing.

THe enlarged diameter portion 31 is provided at an intermediate portion of the inner peripheral surface thereof with a lengthwisely extending recess 39, an upper portion of said recess 39 being positioned in the overlapped relation to the vertical gap 38 so as to permit fluid passage therebetween and a lower portion of said recess 39 being communicated with the lowermost fluid passage 34 by means of a through hole 40 formed in the bushing 32 so as permit fluid passage therebetween. Provided in the wall of the cylinder 11 at an intermediate position of the lengthwisely extending recess 39 is a grease nipple 41 through which lubricating medium such as grease can be supplied into said recess 39.

Reference numeral 42 represents casings each accommodating therein an underwater exhaust system and secured to the both sides of the cylinder 11 by means of fastening members such as bolts 43. As shown in FIG. 2 and FIG. 6, within each of the casings 42, a valve guide 44 is formed for slidably receiving therein a valve body 45 which normally closes a port 47 or 48, formed in the wall of the cylinder 11, under the influence of a spring member 46.

Each of the casings for the underwater exhaust system is formed at its lower wall portion with a plurality of exhaust openings 49 which can be communicated with the port 47 or 48 through guide holes 50, formed in the valve guide 44, as the valve body 45 disengages from the port 47 or 48.

The handle cap 12 as hereinbefore described is provided therein with a valve mechanism 51 of the same or substantially similar construction as provided in the conventional impact hammer. One such conventional valve is described in U.S. Pat. No. 3,398,801, issued Aug. 27, 1968 to Eimatsu Kotone.

It should be noted that reference numerals 47 and 48 represent the port as hereinbefore described, but the port 47 is communicated with the interior of the cylinder 11 while the port 48 is communicated with the interior of the valve mechanism 51 by means of an air passage 53. This air passage 53 is formed in the wall of the cylinder 11 together with another air passage 52 which communicates between the interior of said valve mechanism 51 and the interior of the cylinder 11 through a port 56 formed at an upper portion of the inner peripheral surface of the cylinder.

The cylinder 11 is also formed in its wall with an air passage 54 communicating between the interior of the valve mechanism 51 and a port 55 formed in said cylinder at a position below said port 48.

In this arrangement as hereinbefore fully disclosed, the operation of the impact air driven tool of the present invention is as follows:

Assuming that the piston 15 is positioned below the port 47 as illustrated in FIG. 2, compressed air supplied to a coupling 25 will enter the interior of the handle cap 12 flowing into the air passage 54 through a clearance formed by a valving member of the valve mechanism 51. The compressed air in the air passage 54 will then enter the lower cylinder cavity defined between the lowermost extremity of the piston 15 and the uppermost extremity 33 of the chisel 14, causing the piston 15 to move upwards.

At this time, air contained in the upper cylinder cavity defined between the uppermost extremity of the piston 15 and a lower portion of the handle cap 12 will be discharged through the exhaust openings 49 by means of the guide holes 50 as said air has a tendency to open the valve body 45 through the port 47 upon upward movement of the piston 15.

However, upon further upward movement of the piston with its upper portion subsequently closing the port 47, the air in the upper cylinder cavity will enter through the port 56 into the air passage 52, which in turn pass through the valve mechanism 51 into the air passage 53. The air in the air passage 53 flows through the port 48, pressing the valve body 45 so as to permit said air to be discharged from the exhaust openings 49 through the guide holes 50.

Upon still further upward movement of the piston 15 with its upper portion subsequently closing the port 56, the air in the upper cylinder cavity is compressed as the volume of said cavity is substantially reduced. Then, this compressed air acts to operate the valve mechanism 51 so as to cause the latter to permit the flow into the upper cylinder cavity of compressed air supplied into the handle cap 12 through the coupling 25.

Thus, the piston 15 commences to move downwards, causing air in the lower cylinder cavity to escape to the atmosphere through the exhaust openings 49 by means of the port 47 and then the valve body 45 and at the same time air escapes from an exhaust port provided on the valve mechanism 51 through port 55 and air passage 54. As the piston 15 completely passes through the port 47, the compressed air in the upper cylinder cavity commences to open the valve body 45 to escape to the atmosphere through the exhaust openings 49. However, at the moment when the compressed air in the upper cylinder cavity is reduced, the valve mechanism 51 is operated. It will be thus understood that the chisel 14 is driven by the piston 15 during this time.

As this cycle of operation as hereinbefore fully described is repeated, the chisel is thus continuously driven by the piston 15.

It should be noted that the construction and function of the valve mechanism 51 are substantially so well known by those skilled in the art that the detailed description thereof is herein omitted.

According to the present invention, since the both ports 47 and 48 are normally closed by the valve bodies 45 and, only when air is to be discharged, opened by the action of said air, no water will penetrate into the interior of the cylinder 11 during underwater application, thus enabling the impact air driven tool of the present invention to be utilized in the underwater condition. In case of ground application, the casings 42 and the valve bodies 45, in other words, the underwater exhaust system, may be omitted with the ports 47 and 48 being respectively communicated directly with the atmosphere.

In practice, the impact air driven tool of the present invention must first be operated while in such a normal position that the tip of the chisel 14 is contacted with a subject to be hammered, for example, rock, concrete slab, or the like, and compressed air is then supplied into the handle cap 12 by means of the coupling 25.

If the chisel 14 is driven by the piston 15 while said tool is in the normal position as hereinbefore described, a sufficient amount of impact load will be transmitted to the chisel so that said tool can demonstrate its full destructive power. In the thereto, so long as the tool is correctly handled as hereinbefore described, no collision of the flange 30 on the chisel 14 against an inner end portion of the chisel holder 13 takes place even when he piston 15 drives the chisel 14.

On the contrary, if the chisel is driven by the piston without the tip of the chisel being contacted with the subject to be hammered prior to the commencement of operation, so-called "blank shot" will take place resulting in the collision of the flange 30 against the inner end portion of the chisel holder which may damage the end portion of the chisel holder and/or the flange. Furthermore, an impact of relatively greater value will be loaded on the bolts, accelerating fatigue destruction thereof.

To eliminate the abovementioned disadvantage described in the preceding paragraph, according to the present invention, the cushioning member 27 has been provided within the chisel holder 13. Therefore, it will thus be understood that, when the chisel is downwardly moved by the piston, it will abut against the cushioning member instead of the above-mentioned inner end portion of the chisel holder and, accordingly, the impact of the piston on the chisel does not transmit directly to said inner end portion. This involves prevention of impairment of various parts, including the bolts 16, employed in the impact air driven tool of the present invention with substantial reduction of noises.

This cushioning member 27 is inserted in the chisel holder 13 substantially as illustrated in FIG. 2 and, in case of wear thereof, can be easily replaced.

It has been well known that any impact air driven tools generate considerable vibrations as the piston is fiercely reciprocated within the cylinder assembly so as to substantially ceaselessly drive the chisel. In this instance, under the influence of the vibrations, bolts and nuts employed to connect between the handle cap 12 and the cylinder 11 and between the latter and the chisel holder 13 may be sometimes slackened. However, according to the present invention, this slackening movement can be reliably prevented by the provision of detent means as shown in FIG. 1, FIG. 3, and FIG. 4.

That is to say, the slackening movement or rotational movement of each of the socket members 18 which is rigidly threaded to or integrally formed with the lower end of the corresponding bolt 16 can be reliably prevented by the engagement between the contact surface b and the supporting surface c as shown in FIG. 4. Similarly, the rotational movement of each of the nuts 17 threaded to the upper end of the corresponding bolt 16 can be reliably prevented by the engagement between it and the corresponding opening 21 of the stopper member 20, the detachment of said stopper member 20 being prevented by the collar 22 covering over the nut 17 and restricted by the split pin 24. It will thus be understood that slackening of these bolts 16 and nuts 17 can be prevented.

In case of disassemblying the impact air driven tool of the present invention which may be necessitated for internal examination, it can be easily disassembled by pulling out the split pins 24, removing the collars 22 and then removing the stopper members 20. By removing the bolts 16 and nuts 17 with the aid of a spanner or wrench, it is apparent that the cylinder 11, the handle cap 12 and the chisel holder 13 can be separated.

Furthermore, it should be noted that lubrication must be effected between the inner peripheral surface of the cylinder 11 and the outer peripheral surface of the piston 15 and between the outer peripheral surface of the upper end portion 33 of the chisel 14 and the inner peripheral surface of the bushing.

According to the present invention, for the above-mentioned purpose, the grease nipple 41 has been provided as shown in FIG. 2, through which grease for lubrication can be supplied into the recess 39 formed in the cylinder 11. In this instance, an excessive amount of grease filled in the recess 39 will in turn penetrate into the fluid passages 34 and 35 by means of the through hole 40, thus oiling the contact area between the upper end portion 33 of the chisel 14 and the bushing 32. This excessive amount of grease in the recess 39 will also penetrate into the gap 38, which in turn oils the upper extremity of the bushing 32 through the groove 36.

In this arrangement as hereinbefore described, as the lower cylinder cavity formed between the upper extremity of the chisel and the lower extremity of the piston within the cylinder is pressurized by the compressed air, a portion of the pressure exerted within said cavity may be transmitted to the recess 39 through the groove 36 and then the gap 38. It will thus be understood that the excessive grease in the recess 39 can be forcibly supplied into the fluid passages 34 and 35 by means of the through hole 40 under the influence of the pressure exerted within said cylinder cavity, thus effecting a sufficient lubrication to the contact area between the upper end portion 33 of the chisel and the bushing 32.

Lubrication at the contact area between the cylinder wall 11 and the piston 15 may be practised by a known manner, for example, wherein a suitable oiling device is provided at any desired place on a compressed air supply tubing connected to the coupling 25 so that lubricant may be mixed in and thus supplied by the compressed air to said contact area.

Referring now to FIG. 7 and FIG. 8 in which a slightly modified impact air driven tool of the present invention is shown, the construction wherein a cylinder 61 slidably receiving a piston 64 therein, a chisel holder 63 slidably receiving a chisel 65 therein, and a handle cap 62 are rigidly connected by means of a plurality of bolts is substantially the same as hereinbefore described with reference to FIG. 1 through FIG. 6. Also, the function wherein a valve mechanism 66 disposed within the handle cap 62 is to be operated by compressed air supplied into said handle cap through a coupling 67 by means of a compressed air supply tubing, thereby to act to alternatively supply the compressed air into an upper cylinder cavity above the piston 64 and a lower cylinder cavity beneath said piston 64 so that the chisel 65 may be driven by the reciprocating movement of the piston within said cylinder, is substantially the same as hereinbefore fully described with reference to FIG. 1 through FIG. 6. Valve mechanism 66 may be conventional, such as described in the aforementioned U.S. Pat. No. 3,398,801.

However, in the modified embodiment of the present invention as shown in FIG. 7 and FIG. 8, reference numeral 68 represents a control box rigidly secured to a relatively lower portion of the outer wall of the cylinder 61 and formed therein with a valve chamber, as indicated by 69 particularly in FIG. 8, in which a valve 72 is accommodated. This valve 72 is biased by a spring 71 toward a valve seat 70 formed in an inner wall within the valve chamber 69 and into which one end of a valve rod 80 is extended.

Reference numeral 73 represents a bushing secured at a lower position to the inner peripheral surface of the cylinder 61, through which an upper end portion 74 of the chisel 65 is slidably extended with its flange 75 designed to engage to a lower end of said bushing 73. As particularly shown in FIG. 8, this bushing 73 is formed at its upper portion with an opening 76 in register with the valve rod 80. The opening 76 receives therein an operating member or steel ball 77. It should be noted that an annular edge portion 78 of said opening adjacent to the interior of the bushing 73 is narrowed to give a diameter smaller than that of the operating member 77 so that prevention of falling of the operating member 77 into the interior of the bushing is ensured only with a portion of said member being projected toward said interior.

Extending between the opening 76 to the valve seat 70 on the center line passing from the center point of the valve chamber 69 to the center point of the opening 76 is a guide hole 79 through which the valve rod 80 is slidably inserted. The length of said valve rod 80 must preferably correspond to a distance between one point in which one end of said rod is contacted to the valve 72 seated to the valve seat 70 and the other point in which the other end thereof is contacted with the operating member 77 as substantially shown in FIG. 8.

Reference numeral 81 represents an air inlet and outlet port opened in the cylinder wall at a position where the control box 68 is located, said port 81 being communicated by means of a passage 82 with a spacing defined by the valve 72 and the valve seat engaged by said valve 72. A passage 83 formed in the cylinder wall and the valve chamber 69 are connected to each other by a passage 84 formed in the control box 68 so that the valve chamber is communicated with the valve mechanism 66 disposed within the handle cap 62.

Formed at an intermediate portion of the passage 84 within the control box is a valve chamber 85 communicating to the air outlet and inlet port 81, a portion of said valve chamber 85 adjacent to the port 81 being formed with an annular groove 86 together with a valve port 87 as substantially shown.

This valve chamber 85 slidably receives therein a valve spindle 88 capable of opening and closing the valve port 87 in cooperation with a spring 89 mounted around a portion of said valve spindle 88 that is narrowed to give a diameter smaller than that of the opposite portion of said valve spindle 88. However, it should be noted that the spring 89 normally acts to bias the valve spindle 88 away from the valve port 87.

The other remaining reference numerals 91, 92, and 94 in the drawings represent an air passage communicating the annular groove 86 to the atmosphere, an air passage communicating the valve mechanism 66 to an opening 93 formed at an intermediate portion of the wall of the cylinder 61, and an exhaust port formed at an intermediate portion of the wall of the cylinder 61 for exhausting air to the atmosphere.

In the arrangement as hereinbefore fully described with reference to FIG. 7 and FIG. 8, while the tip of the chisel 65 is pressed to a rock or concrete slab with its flange 75 engaged to the lower end of the bushing 73, the condition as illustrated in FIG. 7 is established wherein the operating member 77 is backwardly collapsed by the upper end portion 74 of the chisel 65 with the result that the valve 72 is moved away from the valve seat 70 by the valve rod 80.

Subsequently, as compressed air is supplied into the handle cap 62 by means of the coupling 67 the valve mechanism 66 acts to guide the compressed air to the air passage 83 and then the air passage 84. As the compressed air thus passes downward in the air passage 84, it acts on the opposite portion or stem portion 90 of the valve spindle 88 within the chamber 85 to cause said spindle 88 to close the valve port 87. At the same time, this compressed air enters the valve chamber 69 and then to the air outlet and inlet port 81 through the passage 82 connecting between said port 81 and the spacing defined by the valve 72 and the valve seat 70. The compressed air supplied to the port 81 will then enter the lower cylinder cavity beneath the piston 64 and thereby to upwardly press the latter.

As the piston 64 reaches at the uppermost limit of its travel, the valve mechanism 66 is actuated to permit the flow of compressed air into the upper cylinder cavity above the piston and concurrently to communicate the passage 83 to the atmosphere, so that the piston commences to downwardly move. Upon further downward movement of the piston, the air contained in the lower cylinder cavity is discharged to the atmosphere through the exhaust port 94. However, as the piston 64 passes through said exhaust port 94, the remaining air contained in the lower cylinder cavity is exclusively discharged to the atmosphere through the air inlet and outlet port 81. It should be noted that, at this time, since pressure within the air passage 84 is equal to the atmosphere, the valve spindle 88 is ready to be moved away from the valve port 87 by the spring 89, even a slight increase of pressure within the lower cylinder cavity in excess of the atmosphere is sufficient to cause the valve spindle 88 to move away from the valve port 87. Therefore, the air contained in the lower cylinder cavity can be discharged to the atmosphere through the air inlet and outlet port 81 by means of the valve port 87, then the annular groove 86 and finally the air passage 91.

So long as the operating member 77 is backwardly collapsed by the upper end portion 74 of the chisel 65 and compressed air is constantly supplied to the handle cap 62, the above-mentioned cycle of operation can be repeated whereby the chisel 65 is fiercely driven by the piston 64 to perform its own services, for example, crushing slabs or rocks.

During the abovementioned cycle of operation, as hereinbefore fully described, the air contained in the lower cylinder cavity is discharged to the atmosphere through the air inlet and outlet port 81 by means of the valve port 87, then the annular groove 86 and finally the air passage 91, as the piston 64 downwardly moves to the lowermost extremity of its travel. The air to be thus discharged travels a relatively shorter distance and, therefore, the backpressure can advantageously be reduced as compared with the conventional impact air driven tool wherein such air is discharged to the atmosphere through such air inlet and outlet port 81 by means of such air passage 83 and then an exhaust opening formed in conventional valve mechanism 66.

In the case where the impact air driven tool of the invention is operated without the tip of the chisel 65 being pressed against a rock or concrete slab, the chisel 65 will be extended to the lowermost limit of its travel with its flange 75 engaged against a lower end portion of the chisel holder 63. While in such condition, when the piston 65 is driven, "blank shot" of the chisel takes place and wrong effects may be imparted on the chisel and the chisel holder. However, so long as the tool is constructed as shown in FIG. 7 and FIG. 8 in accordance with the teachings of the present invention, when the chisel is extended to the lowermost limit of its travel, the operating member 77 is projected toward the interior of the bushing 73 as shown in FIG. 8 with the valve rod 80 being moved toward the operating member 77 by the action of the spring 71 through the valve 72, thereby closing the air passage 82. Thus, it will be understood that the compressed air supplied into the passage 84 from the passage 83 upon commence of the downward movement of the piston 64 is interrupted about the valve seat 70, resulting in that the piston 64 cannot be moved upwardly. Thus, prevention of "blank shots " of the chisel is reliably ensured.

Claims

What I claim is:

1. An impact air driven tool comprising a cylinder including a piston member slidably received therein and capable of being reciprocated by the action of compressed air, a handle cap unit mounted on an upper end of said cylinder, a chisel holding unit including a chisel member slidably supported therein and mounted on a lower end of said cylinder, a plurality of bolts for fastening said cylinder, handle cap unit and chisel holding unit together, and a plurality of nuts each threaded to one end of each of said bolts adjacent to said handle cap, characterized in the provision of a plurality of socket members each threaded to the other end of said bolt adjacent to said chisel holding unit and formed at a portion of its outer periphery with a contact surface engageable with a supporting surface formed in a cut-out portion of the chisel holding unit whereby the relative rotation of said socket member with respect to said supporting surface can be restricted, a plurality of stopper members each having a polygonal opening through which each of said nuts is extended, a plurality of collar members each covering over said nut and formed with a through hole, and a plurality of splint pins each inserted in said through hole of the collar and extending through each through hole formed in said nut whereby said stopper members and collars can be prevented from their disengagement.

2. An impact air driven tool as claimed in claim 1, further comprising a cylindrical cushioning member disposed within a lower portion of said chisel holding unit to permit it to receive a flange formed on an intermediate portion of said chisel member, said cushioning member being made of elastic material.

3. An impact air driven tool as claimed in claim 1, further comprising a valve member disposed in an exhaust port formed in said cylinder unit, said valve member being operable by pressure of exhaust gas to permit the latter to be discharged from said cylinder unit.

4. An impact air driven tool as claimed in claim 1, further comprising a bushing disposed within a lower portion of said cylinder unit, through which bushing an upper end portion of said chisel being slidably received, a storage recess for storing an oiling medium therein and formed in the cylinder wall at a position adjacent to an intermediate portion of said bushing, an oiling nipple provided in the cylinder wall in register with said storage recess for supplying oiling medium into said recess, a gap communicating between said recess to the interior of said cylinder unit, and a plurality of fluid passages formed in said bushing and communicating to said recess by means of a guide hole formed in said bushing.

5. An impact air driven tool as claimed in claim 1, further comprising a valve structure including an operating member loosely received in a lower wall of said cylinder unit and capable of being backwardly collapsed as an upper end portion of the chisel upwardly travels within the cylinder unit and being projected as said end portion of the chisel downwardly travels within the cylinder unit, said operating member while in said backwardly collapsed state permitting the opening of a fluid channel for supply of compressed air into a lower cavity below said piston within the cylinder unit.

6. An impact air driven tool as claimed in claim 1, further comprising an exhaust opening communicating to the atmosphere and formed at a position adjacent to an air outlet and inlet port formed at a lower portion of said cylinder unit and a valve structure disposed at an intermediate position between said outlet and inlet port and said exhaust opening and capable of communicating therebetween only when the gas in the cylinder unit is to be discharged.