Power Driver Device

Abstract

A pressure fluid power driving device for driving studs, nails or the like having a gas chamber including an accumulator piston movable against the force of the gas in the chamber by the action of a noncompressible fluid against the accumulator piston. The invention further relates to the use of noncompressible fluid acting at a first, relatively low pressure to force a brake spool to carry a ram upwardly into sealing engagement with a seat element. The ram is propelled downwardly with great velocity when noncompressible fluid at a second, relatively high pressure, enters the cylinder to urge the accumulator piston against the bias of the compressed gas until a predetermined pressure level is achieved within the cylinder wherein an automatic pressure relief valve system breaks the seal between the top of the drive piston and the seating element allowing the full force of the compressed gas to act on the upper surface of the drive piston through the noncompressible fluid.

Description

BACKGROUND OF THE INVENTION

Power devices having power reservoirs in which a compressible fliud, such as gas, is maintained under pressure and is employed to impart movement ot a noncompressible driving fluid which in turn actuates a suitable driving means, such as a drive piston or hammer, are known and are typified by the power devices disclosed in U.S. Pat. Nos. 2,867,086 and 3,150,488. Other examples of such devices may be seen in U.S. Pat. Nos. 3,636,707 and 3,667,222.

The prior art devices suffer from certain common inherent limitations that prevent them from being commercially acceptable. For example, the prior art devices have been found to experience a large amount of oil leakage from the main power fluid cylinder to the gas chamber. Since the tools in the prior art are primarily displacement sensitive tools, that is, they normally fire when the drive piston has been retracted a predetermined distance into the cylinder, oil leakage into the chamber prevents the tool from firing at predictable, constant energy levels. In addition, the relatively long strokes necessitated by the prior art generate substantial heat within the system which also has an effect on the energy level at which the tool will fire. Since the prior art tools normally operate by retracting the drive piston against the pressure in the gas chamber, the indexing of a fastener beneath the ram must be done quickly or the ram will be energized before the fastener is correctly positioned, thus creating hazardous and unpredictable firing conditions.

SUMMARY OF THE INVENTION

This invention relates to a power driving device having a gas chamber in which a compressible gas is maintained under pressure, an accumulator piston is movable against the bias of this compressed gas to further compress the gas. A drive piston or ram is reciprocally retracted into a cylinder by the introduction of a noncompressible fliud acting on a brake spool which carries the drive piston upwardly into seating and sealed arrangement with a seating element. The drive piston remains in this retracted position to allow the indexing of fasteners beneath the drive piston and until compressible fluid is introduced into the cylinder at a second, higher pressure. When the relatively high pressure noncompressible fluid compresses the gas, through the movement of the accumulator piston, to such an extent that the total pressure built up in the system reaches a predetermined level, a pressure relief valve system allows the upper surface of the drive piston to be exposed to the pressure of the power fluid. The compressed gas, acting through the power fluid as a linkage mechanism, thereafter imparts drive movement to the drive piston, forcing it downwardly in the cylinder at a relatively high velocity.

Additional features of the invention relate to a brake mechanism which first acts to retract the drive piston into a retracted and idling mode and, thereafter, returns to a position in the cylinder for slowing the drive piston down and cushioning the shock of the drive piston as it reaches the extended position.

It is an object of this invention, therefore, to provide a power driving tool in which a compressible fluid, such as gas, is employed to drive a ram, through noncompressible fluid as a linkage between the compressible gas and the upper surface of the ram, at constant energy levels.

A further object of the invention is to provide a power driving tool in which the drive piston is maintained in a retracted position in a cylinder to allow accurate placement of fasteners beneath the ram prior to the introduction of noncompressible fluid to build up pressure in the cylinder to a predetermined pressure level.

Further features of the invention will become apparent to those skilled in the art when the specification is read in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation in partial section of one embodiment of the invention with the drive piston in extended position.

FIG. 2 is a front elevation view of the invention as shown in FIG. 1 taken along line 2--2 of FIG. 1.

FIG. 3 is a front elevation view similar to FIG. 2 showing the brake spool and drive piston in a completely retracted position.

FIG. 4 is a front elevation view similar to FIG. 3 showing the drive piston in a completely retracted position as pressure is built up in the gas chamber.

FIG. 5 is an enlarged end view of a fitting used to connect the gas chamber to the main cylinder.

FIG. 6 is a sectional view of the fitting taken along line 6--6 of FIG. 5.

FIG. 7 is an enlarged sectional view taken across the device, as in line 7--7 of FIG. 4, and showing the pressure relief valve system.

FIG. 8 is an enlarged view of the seating element sealingly engaging the head of the drive piston as shown generally in FIGS. 3 and 4.

FIG. 9 is a partial sectional view of an alternate embodiment of a brake spool for use with the present invention.

FIG. 10 is a fragmentary side elevation view in partial section of an alternate embodiment of the invention.

FIG. 11 is a view of the embodiment shown in FIG. 10 but with the drive piston in retracted position as pressure is built up in the gas chamber.

FIG. 12 is a side elevation view of a second embodiment of a pressure relief valve system for use with the embodiments of the invention shown in FIGS. 10 and 11.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein similar parts are designated by similar numerals, the invention contemplates a new and improved portable power tool device with a cylindrical body including a bore therein and in which is mounted a drive piston or ram and a centrally apertured brake spool surrounding the ram. A stationary seating element is located adjacent the upper extremity of the bore and which is adapted to sealingly engage the upper surface of the drive piston when the drive piston is in a fully retracted position. Also located adjacent the upper extremity of the bore is a reservoir or chamber in which a compressible fluid, such as gas, is maintained under pressure. An accumulator piston is mounted in this chamber for movement against the bias of the compressed gas.

The device operates by introducing power fluid at a first, relatively low pressure, to force the brake spool upwardly, carrying the drive piston with it, into seating engagement with the seating element. With the low pressure fluid in the cylinder, the drive piston remains in the idling mode until such time as the operator of the power device desires to drive a fastener into a workpiece. At that time, compressible fluid is introduced into the cylinder at a relatively high pressure which first forces the brake spool down to the opposite extremity of the bore while maintaining the drive piston sealed against the seat member in a retracted position. As the high pressure oil continues to be pumped into the cylinder, it forces the accumulator piston to move against the bias of the compressed gas, thus, building up the pressure within the cylinder. Upon reaching a certain predetermined pressure in the cylinder, a pressure relief valve opens to permit fluid communication between the power fluid in the clyinder and the upper surface of the sealed drive piston. When this occurs, the full force of the compressible fluid acts through the noncompressible fluid to rapidly extend the drive piston, with great velocity, to drive a fastener which has been indexed beneath the ram.

The power driving device 10 thus includes a cylindrical body portion 12 having a central pass through bore 14. The bore 14 is provided with a counterbore 16 at the upper extremity thereof and a lower counterbore 18. The body 12 is provided, at the upper end, with an external threaded portion for connection with mating threads on the lower cylinder wall portion 42 of a connection fitting element 40. The connection fitting 40 includes a disc shaped body 43, essentially traversing the counterbore 16. The disc shaped body 43 includes a plurality of apertures 49 providing fluid communication between the upper face 46 of the disc shaped body and the lower face 47 of the body. A radially extending bore 45 is provided in the disc shaped body which extends from the central axis of the bore 14 to the outer periphery of the connection fitting 40. Radial port 50 allows communication between one of the apertures 49 and the radial bore 45 for purposes best set forth hereinafter. The lower face of the body 47 includes an annular boss 48 extending generally axially of the bore of the device. This annular boss 48 threadingly engages a generally cylindrical seat element 52. A pass through port 53 extends generally axially of the seat element and permits communication with a cyilndrical projection 54 on the seat element and port 51 in the connection element. The function of cylindrical projection 54 is best set forth hereinafter.

The upper cylindrical wall 41 of the fitting 40 is threadingly mounted to a cap 20. The bore 22 formed in this cap 20 functions as a chamber for compressible fluid, such as gas. Such compressible fluid is introduced into this chamber through a valve member 24. Positioned within bore 22 in the gas chamber is a free floating piston 26. The piston 26 includes an annular recess 28 designed to accommodate a seal 29. The piston 26 rests on a stop, such as the upper surface 46 of the connection fitting, but is free to move upwardly in the bore 22 against the pressure of the compressible fluid.

Positioned within the central bore 14 is power drive piston 30 which includes a generally cylindrical central portion 32 and an enlarged upper end portion 36 which is connected to the central portion by a tapered, frustoconical portion 37. At the opposite end of the central portion 32 is provided a generally cylindrical section of a diameter less than the diameter of central portion and serving as a hammer portion 34. Attention is drawn to the configuration of the upper surface of the end portion 36 as shown most clearly in FIG. 8. This upper end surface is provided with a recess 38 which includes side wall portions 39. It should also be noted that the outer diameter of the cylindrical projection 54 is complementary to the inner diameter of the recess on the head and provides a sealed cooperation between the seating element 52 and the drive piston 30 for purposes which will be set forth hereinafter.

Located within the bore 14 and free to reciprocate therein is a brake mechanism 60. This brake mechanism 60 surrounds the drive piston 30 by the provision of a central bore 62 which accommodates the central portion 32 of the drive piston. This central bore 62 is enlarged slightly at the upper portion of the brake with a counterbore 64. Tapered wall portions 66 connect the counterbore 64 to the central bore 62 and, as will be pointed out in detail hereinafter, the surfaces forming the counterbore and tapered surfaces 64 and 66 are complementary to the external surfaces forming the upper end portion 36 and tapered portion 37 on the drive piston.

Located complementary within the lower counterbore 18 and also surrounding the drive piston 30 is a shock spool element 80. As shown in FIG. 2, the brake 60 rests on the upper surface 81 of the shock spool. For purposes which will be set forth hereinafter, the shock spool is provided with an outer annular recess 83 and a pair of inner annular recesses 84. A plurality of radial ports 85 enables fluid to communicate between the outer recess and the inner recesses. Generally axially extending ports 73 afford communication between the outer annular recess and the upper face 81 of the spool.

At the lower end of the body 12, directly beneath the shock spool 80, is mounted a seal body member 90. Centrally located bore 92 extends through the body member to accommodate the central portion 32 of the drive piston 30. Counterbore 94 in the upper portion of the body 90 accommodates an annular seal which is adapted for sliding engagement with the drive piston 30. An O-ring sealing member 97 is positioned in an annular recess 96 in the counterbore 18.

A nosepiece assembly 91 is attached, preferably removably, to the lower extremity of the seal body 90. This nosepiece may be designed to particularly accommodate various fastener configurations and is merely representative of one design acceptable for use with the power device of the invention.

A feed mechanism 210 may be provided to automatically index fasteners 300 beneath the hammer of the drive piston. A hydraulic line 211 permits noncompressible power fluid entry into a cylinder 216 through port 214. The power fluid acts against the relatively large surface area of the head of the piston 218 to force it to move to the left, as shown in FIG. 1, against the bias of spring 220. A rod-like extension 222 is attached to the piston 218 and is fixedly mounted to a carriage 224 for slidable movement on a track 226. The carriage is provided with a finger 228 having a tip portion 229 adapted to be accepted in a collated strip member with indexable or notch-like grooves. When power fluid is introduced into the cylinder, the piston moves to the left, moving the carriage with it. The finger 229 will have engaged an aperture in a collated strip to move a fastener beneath the path of the ram or drive piston 30. When the oil pressure is released, the spring member 220 forces the piston to the right as shown in FIG. 1 moving the carriage and finger member with it to position the tip of the finger into the next notch in a collated strip. It should be understood that the feed mechanism shown in FIG. 1 is merely representative of a mechanism which may be used with the invention and forms no part of the invention. Feed mechanism such as that shown in U.S. Pat. No. 3,661,313 could be adapted for use with the instant invention.

Turning to FIGS. 1-4, the operational stages of the invention will be described with particular emphasis on the various functional characteristics of the elements recited above. Since an important aspect of the invention is the use of noncompressible power fluid pumped into the system at two pressure levels, the device must be connected with a pump capable of such a dual pressure level operation. Such a pump is not shown and, accordingly, does not form part of this invention in and of itself since a number of acceptable pumping devices are commercially available and known in the art.

The device shown in FIGS. 1 and 2 describes the power drive piston 30 in a fully extended position and represents the mode of the device immediately after it has driven an associated fastener 300. At this point noncompressible fluid, such as oil, is pumped into the cylinder through low pressure line 200 and enters the cylinder through a port 206. The fluid communication provided by port 73 in the shock spool allows the noncompressible power fluid to act on the lower face 68 of the brake spool to carry the drive piston upwardly in the bore 14 until the enlarged head 36 engages the fixed seating element 52. The complementary sealing surfaces provided by the cylindrical projection 54 on the seating element and the recess and side wall portions 38 and 39 in the upper surface of the drive piston allows the power fluid to seal the piston against the seating element. As shown in FIG. 3 and in more detail in FIG. 8, this seal exists as a result of the cross-sectional area of the top edges of side walls of enlarged head portion 36 being substantially less than the surface area of the lower face on the brake spool.

The position of the device shown in FIG. 3 is the idling position of the tool and it should be apparent that this mode allows the ram to be held in a cocked position to facilitate indexing of fasteners beneath the hammer and for proper positioning of the entire device.

To cause the operation of the power device to perform work, such as the driving of a nail, at high velocity, the high pressure level of a two-stage pump is activated through conventional switching means, such as by a trigger 112 in handle 116 serviced by electric lines 117. Hydraulic line 202 allows entry into the system of power fluid at a higher pressure than that pumped used in the mode described in relation with FIGS. 1 and 2. Passageway 208 allows this power fluid to enter the bore 14 through port 204, which is located above the upper surface of the brake spool 60. At this point, the brake spool is forced down under the pressure of the power fluid to its position shown in FIG. 4. However, since the surface area defined by the frustoconical portion 37 on the drive piston is greater than the cross-sectional area of the upper edges 35, any fluid pressure which is exerted on the drive piston tends to hold it in tight sealed engagement with the seating element. As the noncompressible fluid is continued to be pumped into the bore through the port 204, it acts on the lower surface of the accumulator piston 26 through the apertures 49 in the connection fitting 40. As is apparent in FIG. 4, the continued pressure of the noncompressible fluid forces the accumulator piston upwardly against the bias of the compressible gas in the chamber 22. The compressed gas in the chamber normally may have a pressure of approximately 2,000 psi. Upon further compression by the accumulator piston 26, it may attain a pressure of a still higher value of 4,000 psi.

Pressure relief valve system 101 housed in the connection fitting will allow the drive piston to drive fasteners at a predetermined pressure level within the bore 14. Upon the attainment of such a predetermined pressure level, power fluid enters bore 45 in the fitting 40 through radially extending port 50. As will be seen from FIG. 7, bore 45 is provided with a conically shaped valve element 102 having an axially extending stem 103. Also mounted in the bore is a rod member 106 having an annular flange 107 adapted to engage an adjustment screw 108. A compression spring 105 surrounds the rod 106 and stem 103 to bias the valve into seating and sealing engagement with a seat 104. This precludes fluid from entering the bore 45 until the pressure in the bore 14 exceeds the designed force of the spring 105. It is important to note that this force which the valve is held into engagement with the seat 104 may be adjusted external of the cylinder by manipulation of the adjustment screw 108.

Upon the attainment of the pressure sufficient to open the valve 102, power fluid is then free to communicate, through axial port 53 in the seating element, with the recess in the head of the drive piston. This communication effectively allows the drive piston to be urged away from the drive piston and the seating element, breaking the seal there between. Once this seal is broken, the pressure of the power fluid is now exerted across the whole cross-sectional area of the upper end portion 36 on the drive piston and as a result the drive piston is moved forcibly and with great velocity downward due to the force exerted by the high pressure power fluid plus the force of the compressed gas in the gas chamber. Since the power fluid is noncompressible, it serves as a linkage and transfer means for the force being exerted by the compressed gas, through the power fluid, against the enlarged head portion 36 of the drive piston 30.

The drive piston rapidly extends to the position shown generally in FIG. 1. The brake spool 60 is configured to trap over fluid between the counterbore 64 and associated tapered surface 66 and the frustoconical surface 37 of the drive piston, thus slowing the drive piston down as it approaches the end of its power stroke and cushioning the shock of the engagement between head 36 and the brake 60. It will be appreciated that the high energy power stroke will produce surges of oil to be forced downwardly in the bore 14 under great pressure. To decrease this surge of power fluid and its action on seals 95 and 97 in the lower body 90, the shock spool has been positioned in lower counterbore 18. As power fluid is forced downwardly through the shock spool between the internal surface of the bore 87 in the shock spool and the central portion 32 of the drive piston, it may be released to the low pressure return line 202 through inner annular recess 84 and the plurality of radial ports 85 communicating between these inner annular recesses and an outer annular recess 83. Thus the substantial surge of power fluid and its action on the lower seals is decreased.

Due to the configuration of the upper seal surface of the recess 38 in the drive piston 30, it is possible that power fluid may become trapped within this recess and tend to prohibit effective sealing engagement between the drive piston and the seating element. For this purpose, a bleed valve system is provided in the seating element. Attention is drawn to FIG. 8 which shows a radial port 55 extending from the centrally located axial port 53 providing fluid communication with a recess accommodating a ball valve 56. This ball valve is resiliently seated at a predetermined force through the use of an annular resilient seal 57. It should be apparent that any oil trapped in the recess 38 will be forced out through the radial port 55, however due to the ball valve 56 and seal 57 power fluid may not enter the recess from the main cylinder.

A modification of the invention is shown in FIGS. 10-12 wherein the use of similar numerals with the addition of the suffix a are intended to designate similar elements or components. The power device design 10a is particularly effective to provide a driving tool which is compact in size and which is particularly designed to generate a high velocity in the drive piston 30a.

The essential distinction between device 10 and device 10a resides in the provision of an accumulator piston 26a having a central bore 127 and which includes an annular boss 128 and annular flange 129. The annular flange includes both an inner and outer annular recess 125 to accommodate sealing O-rings. The accumulator piston 26a is retained and slidably mounted on a post element 140. Thus, the piston 26a is free to move in a telescoping fashion relative to the post 140 and within the gas chamber 22a. The telescoping motion of the accumulator piston 26a is due to the urging of a high pressure noncompressible fluid forcing the accumulator piston upwardly as shown in FIG. 11 against the bias of a compressible fluid in the gas chamber 22a. In this embodiment the accumulator piston is restrained from movement into the bore 14a of the cylindrical body 12a by the upper counterbore 16a functioning as an abutment surface in a manner similar to the upper surface of the fitting 40 in the embodiments of FIGS. 1-4.

The device 10a is provided with a pressure relief valve system to allow the drive piston to be actuated upon the pressure in the cylinder reaching a predetermined level. Post 140 includes an axial port 142 and a series of counterbores 144, 145 and 146. Positioned within the counterbore 145 is a cup-like bearing member having an aperture at the lower surface thereof to permit a valve rod 152 to reciprocate therethrough. The valve rod includes an integral head 156 and a rod portion 160 extending upwardly from the head. A spring member 158 is mounted around the rod 160 and is supported by the head portion at one extremity of the spring and impinges an adjustment screw member 162 at the other extremity. Valve rod 152 is positioned in counterbore 146 for slidable movement therein. A suitable seal is positioned within counterbore 144. At the lower extremity of this rod 152 is provided a conical valve surface element 154 which sealingly engages the seat portion 150 against the normal bias of the spring 158. Radial port 165 provides fluid communication between the bore 14a and the counterbore 146 and with the shoulder 167 formed at the juncture extremity of rod 152 and valve 154. As the pressure in the cylinder is increased, in a manner similar to the process described relative to FIGS. 1-4, the power fluid will exert a force on the shoulder 167 until the pressure in the cylinder overcomes the predetermined force of the spring 158. At this point, fluid communication is provided between the bore 14a and the recess 38a in the drive piston. At this instant the seal is broken between the head of the drive piston and the complementary projection 143 in the post 140. Once the seal has been broken, the full force of the compressed gas acting through the linkage of the power fluid propels the drive piston rapidly downwardly to drive an associated fastener.

It should be noted that hammer portion 34a is a blade-like extension providing a fastener contacting cross-sectional area of a generally rectangular configuration to better accommodate staple-like fasteners.

Attention is directed to the bore 131 provided in drive piston 30a. This decreases the mass of the drive piston while retaining the effective area which may be subjected to power fluid pressure. Thus, the velocity of the ram may be substantially increased as a result of this design.

Attention is also directed to FIG. 12 wherein an alternate embodiment of the post assembly 140 and pressure valve system is described. Assembly 240 is provided with an axial bore 242 having counterbore portion 244. An annular body 270 is slidably mounted in counterbore 244. Body 270 includes a recess 272 which accommodates an O-ring seal 274. The body also includes a projection 275 which extends axially of body 270 in the counterbore 244 and which is surrounded by the upper portion of a compression spring 258. Slidably mounted in the counterbore 243 is a conical valve member 254 having a projection 255 extending toward and generally along the same axis as the projection 275. Compression spring 258 surrounds projection 255 and retains the valve in sealing engagement within the seat surface 250 until such time as the power fluid in the cylinder reaches a predetermined pressure greater than the force exerted by the spring 258. At this instant the power fluid, through port 238 and axial port 242, forces the valve member upwardly allowing fluid communication to longitudinally extending port 232. In this manner the power fluid contacts the recess 38a, breaking the seal between the post 240 and the head 36a of the piston 30a. The breaking of this seal allows full force of the power fluid to rapidly propel the drive piston.

In the event the accumulation of oil within the cavity 131 and recess 38a prevents sealing engagement with the post means, a one-way bleed valve system is provided. The oil trapped in recess 38a may be forced into radially directed ports 234 and out into the bore 14a through the one-way valve system provided by an annular resilient seal 236.

The operation of driving device 10a is similar to the operation of device 10 in that low pressure power fluid is pumped into bore 14a through port 206a and also through the shock spool 80a. The lower pressure power fluid thus forces the brake spool 60a to carry the drive piston 30a up in the bore into seating engagement with a post 140. This position is shown in FIG. 10 and, as is described relative to the embodiments shown in FIGS. 1-4, shows the power driving device in an idling position.

When the tool is to be actuated, the oil pump is switched to the high pressure mode and oil at a relatively high pressure enters the bore 14a through port 204a and, by virture of a longitudinal recess 119 in the bore, it is permitted to both impinge the lower surface of the accumulator 26a and the upper surface of the brake 60a. Under this relatively high pressure power fluid, the brake spool is forced downwardly to rest against the upper surface of the shock spool 80a while the accumulator piston is forced to move up against the bias of the compressed gas in the accumulator chamber 22a, as shown in FIG. 11. When the pressure of power fluid reaches a certain predetermined level, the pressure relief valve system described above allows the seal to be broken between the drive piston and the post 140 thus subjecting the full force of power fluid on the upper relatively large surface area of the drive piston 30a, thus driving the piston rapidly downwardly.

FIG. 9 shows an alternate detail of a brake spool which may be used with either of the embodiments of this invention. The spool 70 has a central pass through bore 72 to accommodate the central portion 32 of the drive piston 30. Counterbores 74 and 75 and frustoconical portions 76 and 77 act together to cushion the shock of the engagement of the head of the drive piston 36 and the brake 70. However, due to the plurality of differeing volumetric capacities in the head of the brake spool created by the counterbores 74 and 75 and tapered surfaces 76 and 77, the drive piston is allowed to transmit high energy levels toward the end of its driving stroke, rather than initiating retardation early in the drive stroke.

A further feature of the brake spool 70 is the provision of a plurality of circumferentially spaced ports 73 extending generally along the axis of the brake. An equal plurality of radially directed ports 71 are connected with the axial ports to permit fluid communication between the lower surface of the brake 70 and annular recess 79 which accommodates a resilient O-ring seal 78 around the periphery of the brake. Thus, when the driving tool is in the idling position, as shown in FIGS. 3 and 10, low pressure fluid is allowed to circulate through ports 71 and 73 and through the one-way valve system 79 to effectively cool the system when the tool is in the idling mode.

It will now be apparent that the power driving device illustrated and described performs work due to the expansion of compressed gas in a power accumulator or gas chamber. The pressured gas introduced in the gas chamber may be initially of a relatively large value, for example 2,000 psi, and compression of the gas in the chamber due to the movement of an accumulator piston 26 by a non-compressible power fluid, causes it to attain a pressure of a still higher value approximately 4,000 psi. Thus, the energy stored in the compressed gas is employed to drive a piston 30 using the non-compressible power fluid as a linkage between the drive piston and the accumulator piston. The power driving tool utilizes compressible power fluid at two distinct pressure levels. Power fluid at a first relatively low pressure is used to retract the drive piston by forcing the brake spool to carry the drive piston up into seating and sealing engagement with a stationary member. The drive piston is retained in the idling mode by the relatively low pressure compressible fluid until such time as the operator of the tool desires to drive a fastener. At that time noncompressible fluid is pumped into the bore 14 forcing the brake spool down in readiness to accept and cushion the drive piston while the drive piston remains in sealing engagement with the seat element. Pressure is built up in the system by increased entry of the compressible fluid which forces the accumulator piston to move against the bias of the compressed gas. A further significant feature of the invention is the provision of an adjustable pressure relief valve system which allows the drive piston to be actuated to release energy at a certain predetermined and repeatable pressure level. Thus, the energy level which fasteners are driven will be constant and neither the change in temperature within the system nor the leakage of oil within the gas chamber will affect the energy level at which the piston is driven.

It will be apparent to those skilled in the art that an economical, compact, high velocity, high force is provided which drives fasteners at a predictable energy level and in such a manner that collated fasteners may be indexed beneath the driving ram in a safe, efficient manner. Where all the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.

Claims

I claim:

1. A power device including a body having a bore, a drive piston having an enlarged head portion mounted in the bore for reciprocating movement therein, an accumulator piston mounted adjacent the bore for limited reciprocating movement independent of the drive piston, means for biasing the accumulator piston downwardly toward the drive piston, stationary stop means in the bore adapted to limit the downward movement of the accumulator piston, stationary seat means mounted in the bore adapted to sealingly contact the upper surface of the enlarged head portion, means to urge the drive piston upwardly into sealing contact with the seat means, means for introducing a noncompressible power fluid into the bore to urge the accumulator piston upwardly against the force of the biasing means, adjustable pressure relief valve means associated with the seat means and providing a passage from the bore through the seat means to the top of the head portion when a predetermined pressure has been built up in the bore, wherein the power fluid acting on the top of the head through the passage breaks the sealing contact between the seat and head and allows the force of the biasing means, through the power fluid, to urge the drive piston downwardly with great velocity.

2. A device of the type claimed in claim 1, wherein a brake means encircles the drive piston and is adapted to limit the downward extension of the drive piston as it is driving under the force of the biasing means and also serves to cushion the drive piston when it reaches its extended position.

3. A device of the type claimed in claim 1, wherein the means urging the drive piston into sealing contact includes a non-compressible power fluid which enters the bore and acts on the lower surface of the head portion to force it into contact with the seat means.

4. A device of the type claimed in claim 2, wherein a brake spool encircles the drive piston and the means for urging the drive piston upwardly includes a noncompressible power fluid which enters the bore in such a position to contact the lower surface of the brake spool wherein the brake spool carries the drive piston upwardly into seating position.

5. A device of the type described in claim 1, wherein the upper surface of the enlarged head portion is recessed to form an open ended chamber having side walls and a bottom wall and the seat means includes a projection dimensioned to sealingly engage the recessed head portion.

6. A device of the type described in claim 1, wherein the body includes a passage means adjacent the seat means to allow non-compressible power fluid to urge the accumulator piston against the force of the biasing means.

7. A device of the type described in claim 1, wherein the seat means is mounted at the uppermost portion of the bore and extends axially downwardly a short distance and having a terminal portion which includes a sealing projection, the seat means including an axially direct port means at the sealing projection and a radially directed port means spaced axially above the sealing projection, said port means each communicating with a valve seat, a valve member associated with the valve seat and maintained therein against the force of an adjustable biasing means, wherein the radially directed port means provides communication with the axially directed port means and the sealing projection when the pressure in the bore exceeds the predetermined pressure level of the adjustable valve biasing means.

8. A power device including a body having a main cylinder, a drive piston reciprocably movable in said main cylinder, said piston having an end portion extendable outwardly from one extremity of the main cylinder through a seal means, said piston including an enlarged head portion at the opposite end thereof, stationary seat means in the body adjacent the other extremity of the cylinder for sealingly engaging the head portion of the drive piston, an accumulator chamber mounted adjacent the seat means, an accumulator piston slidably mounted within the accumulator chamber, compression means in the accumulator chamber to bias the accumulator toward a fixed stop means at one extremity of the chamber, the stop means restricting movement of the accumulator piston toward the main cylinder, means introducing noncompressible power fluid at different pressure levels to the main cylinder, relief valve means associated with the seat means providing fluid communication between the main cylinder and the sealed face of the head portion at a predetermined pressure level after the head of the drive piston has been moved into sealing engagement with the seat means, wherein noncompressible power fluid may be introduced into the main cylinder at one pressure level to force the drive piston to move to a retracted position in sealing contact with the seat means and thereafter allow noncompressible power fluid to enter the main clyinder at a second, higher pressure level to force the accumulator piston to move against the bias of the compression means and also break the seal between the drive piston and the seat means allowing the compression means to move the drive piston from the retracted position to an extended position.

9. A power device in accordance with claim 8, which includes a cap member mounted at one extremity of the main cylinder and forming the accumulator chamber.

10. A power device in accordance with claim 9, which includes a post mounted in the cap and extending downwardly into the accumulator chamber generally along the axis of the accumulator chamber and main cylinder, the free extremity of said post forming the seat means, said post also including the relief valve means providing communication, at a predetermined pressure level, between the main cylinder and the seat means.

11. A power device in accordance with claim 9, wherein the accumulator piston is slidably mounted around a post extending axially of the accumulator chamber.

12. A device in accordance with claim 8, which includes a brake spool mounted around the drive piston for reciprocating movement within the main cylinder.

13. A device in accordance with claim 12, including a shock spool mounted at the lowermost extremity of the main clyinder, said shock spool having a central aperture adapted to receive the shank portion of the drive piston, port means in said aperture providing fluid communication with a reservoir, whereby noncompressible fluid trapped beneath the brake spool will be forced into the reservoir.

14. A device in accordance with claim 13, wherein the shock spool includes an annular recess on its inner periphery communicating through the port means with an annular recess formed on the outer periphery of the shock spool.

15. A device in accordance with claim 8, wherein the enlarged head portion of the drive piston is provided with a recess defined by an upstanding sidewall portion, said seat means being provided with a complementary protuberance adapted to at least partially fill the recess in sealing arrangement therewith, said seat means also being provided with passage means for releasing power fluid which may become trapped in said recess.

16. A device in accordance with claim 15, wherein the passage means includes port means communicating with an annular recess axially spaced from the protuberance, a resilient sealing member mounted in said annular recess to serve as a check valve for the exiting power fluid.

17. A power driving tool including a cylinder portion having a drive piston reciprocably mounted therein, the drive piston extending through a brake spool also adapted for reciprocable movement within the cylinder, a stationary seat means positioned at one extremity of the cylinder and adapted to sealingly engage an enlarged head portion of the drive piston, an accumulator chamber operatively mounted adjacent the seat means and having an accumulator piston slidably mounted therein, compression means in the accumulator chamber acting on one face of the accumulator piston to bias it toward the main cylinder, first means for introducing noncompressible power fluid at a given pressure into said cylinder to move said brake spool and drive piston toward the seat means and force the drive piston into sealing contact with the seat means to hold the drive piston in a retracted position, second means for introducing noncompressible power fluid at a second, higher pressure into the main cylinder to force the accumulator piston to move against the bias of the compression means and urge the brake downwardly in the main cylinder, relief valve means associated with the seat means to allow the noncompressible power fluid to contact the sealed surface of the head portion of the drive piston thus breaking the seal between the head portion and seat means at a predetermined pressure and allowing the compression means to move the drive piston rapidly from a retracted position to an extended position to drive a fastener associated with the tool.

18. A driving tool in accordance with claim 17, wherein the drive piston includes an intermediate portion and a terminal hammer portion, the intermediate portion having a diameter which is less than the diameter of the head portion.

19. A driving tool in accordance with claim 18, wherein the terminal portion is generally cylindrical and is of a smaller diameter than the diameter of the intermediate portion.

20. A driving tool in accordance with claim 18, wherein the terminal portion is a generally flat, blade-like member.

21. A driving tool in accordance with claim 18, wherein the drive piston includes a counterbore extending downward a substantial distance into the intermediate portion.

22. A method of producing driving energy of the type required to drive a fastener, including the steps of moving a drive ram having an enlarged head in one direction in a bore through the introduction of power fluid into the bore at a first pressure through a first port to position the ram in seated position on a stationary seat member in the bore, feeding a fastener beneath the ram after the ram has been seated, introducing a power fluid through a second port at a second pressure which is greater than said first pressure while the head of the ram is seated on said seat member to move a piston against a bias, and which is sufficient to open a relief valve to provide communication between the bore and the seated surface of the enlarged head of the ram to expose the head of the ram to the power fluid and force of the bias against the piston thereby driving the ram downwardly to contact and drive the fastener.