Fastener Driving Apparatus Operable Under Pressure Conditions Greater Than Line Pressure

Abstract

A fastener driving apparatus in which the fastener driving means in the form of a piston and piston rod construction is mounted within a cylinder which is movable from a first position into a second position by fluid pressure in the reservoir of the apparatus, while the fastener driving means is maintained in a fastener receiving position. Movement of the cylinder from the first position to the second position establishes a negative pressure beneath the driving piston and/or a pressure equal to reservoir pressure or greater than reservoir pressure above the driving piston so that when the fastener driving means is released it will move from the fastener receiving position into a fastener driven position under differential pressure conditions which are greater than reservoir pressure above the piston and atmospheric pressure below the piston. The apparatus is actuated by a work contacting member and a trigger member through an interlock means which effects movement of an actuating valve into an actuating position in response (1) to the simultaneous movement of the work contacting and trigger members into their operative positions, (2) to the movement of the work contacting member into its operative position when the trigger member is in its operative position or (3) to the movement of the trigger member into its operative position when the work contacting member is in its operative position. The interlock means comprises an elongated interlock member having a transversely extending slot formed in the central portion thereof through which a pivot pin carried by the housing is disposed, one end of the interlock member having a lost motion connection with the work contacting member and the other end of the interlock member having a lost motion connection with the trigger, the interlock member including an actuating valve engaging portion intermediate the ends thereof.

Description

This invention relates to fastener driving apparatus and more particularly to fluid pressure actuated fastener driving apparatus.

In the past several years fluid pressure actuated fastener driving devices have been brought into increasingly frequent use in many industries. A common characteristic of these fastener driving devices is the provision of a fastener driving element which is moved through a fastener driving stroke and a return stroke by means of a driving piston reciprocably operable within a driving cylinder. Conventionally, the handle of the device is constructed to provide a reservoir for receiving fluid under pressure from a suitable source. Various control valve assemblies have been provided to direct the fluid under pressure within the reservoir selectively to the driving cylinder to effect the driving stroke of the piston and in many instances the return stroke as well. In the known prior art devices, the driving stroke of the driving piston is accomplished by the application of fluid under reservoir or line pressure.

Where relatively small fasteners are to be driven by the device, the application of reservoir or line pressure to the driving piston to effect the driving stroke has proven entirely adequate. However, with the development of fluid pressure actuated fastener driving devices which are capable of handling large fasteners, as, for example, nails up to 16-penny and higher, there exists a greater need for effecting the driving stroke of the driving piston under a pressure which is greater than pressures conventionally available to operate the lighter duty devices in the interest of acceptable size and weight considerations. While it would be possible to simply increase the pressure available at the source, such an increase in the fluid pressure available can not always be economically obtained.

An object of the present invention is the provision of a fluid pressure operated fastener driving apparatus which is operable from a source of fluid under pressure of the type heretofore utilized in conjunction with light duty fastener driving apparatus having means operable by fluid under reservoir or line pressure for establishing an increased pressure differential within the driving cylinder acting on the driving piston to effect the driving stroke of the driving element of the device.

In accordance with the principles of the present invention, this objective can be achieved by establishing a pressure greater than reservoir or line pressure within the driving cylinder acting on the driving piston in a direction to move the driving element through its driving stroke and/or the establishment of a negative pressure condition within the driving cylinder acting on the driving piston in a direction to move the driving element through its driving stroke. It is preferable in accordance with the present invention to establish both a pressure greater than reservoir or line pressure and a negative pressure acting on the driving piston, although the objectives of the present invention can be obtained by establishing a pressure greater than reservoir or line pressure on the driving side of the driving piston and an atmospheric condition on the opposite side of the piston, as well as the establishment of line pressure on the driving side of the driving piston and a negative pressure condition on the opposite side thereof.

It is of significant importance that the device of the present invention achieves the aforementioned objectives with a construction providing weight and size characteristics which are entirely acceptable. The relationship of the weight and size characteristics to the high energy output characteristics compares favorably with the relationship of these characteristics in light duty devices. Consequently, while the principles of the present invention have particular advantages where high output energies are required they may also be advantageously employed in devices limited to light duty operation.

Moreover, the present invention, while being particularly suited to the higher energy requirements of medium to heavy duty fastener driving devices, provides significant operational advantages which would be applicable to light duty devices as well. It is desirable in all fastener driving devices that the operational cycle including the driving stroke be completed as fast as possible, with as little noise as possible, and with as little recoil action on the hand of the operator as possible. These desirable operational characteristics are achieved in accordance with the principles of the present invention by eliminating the necessity of displacing and discharging air during the driving stroke, by imparting a relatively high velocity to the driving piston through the increased pressure differential established and by maintaining a very favorable ratio of the moving mass of the device (the driving piston and the driving element) to the static mass thereof (the remaining structure).

Accordingly, it is a further object of the present invention to provide a fastener driving device capable of high speed operation which is quiet and substantially recoilless.

A still further object of the present invention is the provision of a fluid pressure operated fastener driving device of the type described having improved means for maintaining the driving piston and the fastener driving element in a fastener receiving position during the establishment of the above-mentioned pressure conditions within the driving cylinder and for releasing the driving piston and fastener driving element from said fastener receiving position so that the fastener driving element will be moved through its fastener driving stroke, at least initially, under the action of the established pressure conditions.

Another object of the present invention is the provision of a fastener driving apparatus of the type described having an improved contact trip-trigger interlock mechanism capable of "drag" and "bump" firing the apparatus and operable to prevent manual actuation of the fluid pressure driving system when the device is not in contact with a workpiece.

These and other objects of the present invention will become more apparent during the course of the following detailed description and appended claims.

The invention may best be understood with reference to the accompanying drawings wherein an illustrative embodiment is shown.

In the drawings:

FIG. 1 is a vertical sectional view of a fluid pressure operated fastener driving apparatus embodying the principles of the present invention, showing the parts in their normally inoperative position;

FIG. 2 is a view similar to FIG. 1 showing the position of the parts after contact trip-trigger actuation, but prior to the release of the fastener driving element;

FIG. 3 is a view similar to FIG. 2, showing the position of the parts at the start of the return stroke of the fastener driving element immediately after the driving stroke thereof;

FIG. 4 is an enlarged fragmentary vertical sectional view of the upper head portion of the apparatus illustrating the valve mechanism of the fluid pressure return means of the apparatus in a position prior to the connection of the apparatus with a source of fluid under pressure;

FIG. 5 is an enlarged fragmentary sectional view taken along the line 5-5 of FIG. 1, with parts broken away for purposes of clearer illustration;

FIG. 6 is an enlarged fragmentary vertical sectional view illustrating the latch pin of the apparatus in its latching position retaining the fastener driving element in its fastener receiving position;

FIG. 7 is a view similar to FIG. 6 showing the fastener driving element moved into a release position wherein the latch pin is movable into its release position to permit the fastener driving element to move through its driving stroke;

FIG. 8 is an enlarged fragmentary sectional view taken along the line 8-8 of FIG. 1;

FIG. 9 is an enlarged fragmentary sectional view taken along the line 9-9 of FIG. 1; and

FIG. 10 is an enlarged fragmentary sectional view taken along the line 10-10 of FIG. 1.

Referring now more particularly to the drawings, there is shown therein a fluid pressure operated fastener driving apparatus, generally indicated at 10, embodying the principles of the present invention. In general, the apparatus comprises a main housing, generally indicated at 12, having drive track means, generally indicated at 14, at one end thereof which is adapted to receive laterally therein a fastener F from a supply S of such fasteners carried by and fed thereto from a magazine assembly, generally indicated at 16.

The apparatus also includes a fastener driving member or element 18 operatively connected with a fastener driving piston 20 and a driving chamber assembly, generally indicated at 22, including a cylinder member 24 within which the driving piston is reciprocably mounted. Means, generally indicated at 26, is provided for retaining the fastener driving member 18 in a fastener driving position wherein a fastener F from the supply S is fed from the magazine 16 laterally into the drive track to be driven longitudinally outwardly therefrom and for releasing the fastener driving element from the fastener driving position so as to permit the latter to be moved through its driving stroke to drive the fastener F in the drive track 14 longitudinally outwardly therefrom and into the workpiece.

In accordance with the principles of the present invention, the apparatus 10 includes means, generally indicated at 28, operable by fluid under pressure from a suitable source (not shown) under the control of the operator for establishing a pressure condition within the driving cylinder acting on the driving piston when the fastener driving element is in its fastener receiving position, which pressure condition includes the establishment of a pressure greater than line pressure on the driving side of the driving piston and/or a negative pressure condition on the opposite side of the driving piston.

The apparatus preferably provides a contact trip-trigger interlock mechanism, generally indicated at 30, which is operable to permit actuation of the apparatus only when the same has been moved into operative contact with the workpiece into which the fastener is to be driven, and has also been manually actuated by the operator, and a fluid pressure operated means, generally indicated at 32, for effecting the return stroke of the fastener driving apparatus in response to the release of the contact trip-trigger interlock mechanism. The mechanism 30 is operable to permit "drag" firing wherein the apparatus is maintained in contact with the workpiece while being dragged or moved therealong in conjunction with repeated manual actuation or "bump" firing wherein the apparatus is continuously manually actuated and repeatedly moved into and out of engagement with the work piece at spaced positions thereon.

As best shown in FIG. 1, housing 12 includes a longitudinally extending head portion 34 defining an exhaust chamber 36 at the end thereof adjacent the drive track means 14 and a longitudinally aligned cylindrical pressure chamber 38 separated from the exhaust chamber 36 as by a radially inwardly extending flange section 40.

The housing 12 also includes a handle portion 42 extending transversely outwardly from the longitudinally extending head portion 34 at a position intermediate the ends thereof. The handle portion 42 is exteriorly configured to be exteriorly grasped within the hand of the operator and is configured interiorly to provide a chamber or reservoir 44 adapted to be connected to a source of fluid under pressure, as by an interiorly threaded opening 46. The handle portion 42 also provides a generally parallel interior exhaust chamber 48 having an interiorly threaded outlet 50 to which a silencer (not shown) may be secured, if desired.

The drive track means 14, as shown, is formed as part of the magazine assembly 16. The drive track means 14 and magazine assembly may be of any suitable construction to accommodate any desired form of fastener. For example, a magazine and drive track assembly of the type illustrated in commonly assigned U.S. Pat. No. 3,259,292, dated Jul. 5, 1966, may be utilized for accommodating a fastener package of the type described in commonly assigned U.S. Pat. No. 3,083,369, dated Apr. 2, 1963. However, as shown, the magazine assembly 16 is of conventional construction of the type adapted to receive a straight stick of fasteners of conventional T-head design, the drive track means 14 being interiorly configured to accommodate the shape of the fasteners. As shown, the magazine assembly 16 includes a section 52 which is adapted to engage within the adjacent end of the exhaust chamber 36 of the housing. Any suitable means may be provided for securing the section 52 in proper relation to the exhaust chamber 36, as, for example, by bolts 54 extending through the section 52 and threadedly engaged within the adjacent end of the head portion 34 of the housing.

While the driving chamber assembly 22 may take many forms, as shown, it preferably includes an outer cylindrical member 56 disposed in surrounding relation to the cylinder member 24 so as to define therewith an annular high pressure chamber 58. The end of the high pressure chamber 58 opposite from the drive track 14 communicates with the interior to the cylinder member 24 by any suitable means, such as a plurality of circumferentially spaced generally rectangularly shaped openings 60 formed in the cylinder member 24. The opposite end of the chamber 58 is closed by any suitable means, as, for example, an O-ring seal 62 disposed within an inwardly opening annular groove 64 formed in the adjacent end of the cylinder member 56. The O-ring seal 62 extends radially from the groove 64 into pressure tight engagement with the exterior periphery of the cylinder member 24 at the adjacent end thereof.

The means 26 for retaining the fastener driving element 18 in its fastener receiving position and for releasing the fastener driving element 18 from such position for movement through its driving stroke may likewise take many forms. As best shown in FIGS. 1--3 and 5--7, the means 26 preferably includes a cylindrical latch member or latch pin 66 disposed with its axis extending perpendicular to the longitudinal axis of the head portion 34 of the housing and mounted in the section 52 for transverse movement between a latching position and a releasing position.

As best shown in FIG. 5, the section 52 is provided with an elongated recess 68 which opens toward the exhaust chamber 36 and communicates with the inner end of the drive track means 14 at the central portion thereof. Disposed within the bottom of the recess 68 is a member 70 which carries the latch pin 66 for movement between its latching and releasing positions. As shown, the latch pin carriage member 70 has formed in one end portion thereof an elongated slot 72 of a size to receive therein the latch pin 66. The opposite end portion of the member 70 is apertured to receive a pivot pin 74 fixedly carried by the section 52 and extending into the recess 68.

The section 52 has a bore 76 extending therethrough into communication with the recess 68 adjacent one side of the member 70 within which a spring pressed plunger 78 is slidably mounted so as to engage the adjacent side of the member 70 and resiliently urge the latter in a counterclockwise direction as viewed in FIG. 5. As shown, the spring pressed member 78 is formed with a central recess which receives one end of a coil spring 80, the opposite end of which engages a plug 82 threadedly engaged within the outer end of the bore 76.

The spring pressed member 78 serves to resiliently bias the member 70 into a limiting position wherein the latch pin is disposed in its latching position. To this end, and adjustable stop member 84 is threadedly engaged within a bore 86 formed in the section 52 in communication with the recess 68 adjacent the opposite side of the member 70. As shown in FIG. 5, the end of the stop member may be threadedly adjusted within the bore 86 so that the inner end thereof will engage the adjacent side of the member 70 to limit its counterclockwise movement under the biasing of the spring pressed member 78.

The side of the member 70 adjacent the stop member 84 is cut away, as indicated at 88, in communication with the central portion of the latch pin receiving slot 72. Mounted within the outer portion of the recess 68 is a fixed guide member 90 having an opening 92 extending through the central portion thereof which is shaped to receive the fastener driving element 18 and to permit a limited amount of lateral movement of the fastener driving element therein in a direction perpendicular to the axis of the latch pin.

As best shown in FIGS. 6 and 7, the fastener driving element 18 is preferably circular in cross section and has its fastener engaging end formed into a semispherical configuration, as indicated at 94. When the latch pin 66 is disposed in its latching position, the axis of the latching pin is disposed slightly to the right of the axis of the fastener driving element 18, as viewed in FIGS. 1 and 6, the rounded configuration of the engaging portions of the end 94 and latch pin 66 tend to move the latch pin to the right, as viewed in these FIGS., in a direction to engage the carriage member 70 with the stop 84.

The latch pin is movable from its latching position into its releasing position to permit the fastener driving element 18 to move through its driving stroke by effecting a relative transverse movement between the latch pin and the end of the fastener driving element in a direction to move the axes of the latch pin and the fastener driving element relatively into alignment and then beyond such position of alignment so that the force applied to the fastener driving element can then operate to cam the latch pin completely into its release position against the action of the spring pressed member 78. The accomplishment of the above-mentioned relative movement may be achieved in various different ways after the means 28 has been operated to establish the essential pressure conditions acting on the driving piston. Thus, the relative movement can be accomplished either by effecting transverse movement of the latch pin or the fastener driving element, or both, at the desired time. Such relative movement can be accomplished through manual actuation, fluid pressure actuation, or mechanical actuation.

As shown, the required movement is accomplished by effecting a transverse movement of the fastener driving element in response to the positioning of the driving chamber assembly into the position it assumes when the essential pressure conditions acting on the driving piston have been established. This relative movement is accomplished by means of a cam roller 96 mounted within a projecting portion 98 formed in the exhaust chamber 36 at the end thereof adjacent the drive track means 14.

Preferably, the cam roller 96 is mounted within the projecting portion 98 so as to be maintained in any one of a plurality of longitudinally adjusted positions. The adjustment may take many forms and, as shown, comprises simply a shaft 100 for the cam roller 96 which may be selectively mounted within any one pair of a series of aligned pairs of longitudinally spaced openings 102 formed in the transversely spaced walls of the projecting portion 98. It will be noted that a portion of the wall of the outer cylindrical member 56 of the driving chamber assembly 22 is frustoconically shaped, as indicated at 104, to cooperate with the surface of the cam roller to effect the transverse movement of the fastener driving element 18 to effect movement of the latch pin 66 out of its latching position and into its releasing position.

The means 28 for establishing the essential pressure conditions acting on the driving piston may likewise take many forms and, as shown, includes a pistonhead structure, generally indicated at 106, which forms a part of the driving chamber assembly 22. As shown, the outer cylindrical member 56 of the driving chamber assembly 22 is formed with an enlarged flange portion 108 at the end thereof opposite from the surface 104. Mounted within the flange portion 108 in sealing relation thereto, as by O-ring seal 110, and in abutting relation to the adjacent end of the inner cylinder member 24 is a pistonhead member 112. The member 112 includes a radially outwardly extending annular flange 114 disposed in abutting engagement with the adjacent end of the flange portion 108 and is apertured to receive a plurality of fastening elements 116 threadedly engaged within the flange portion 108 to secure the pistonhead member 112 thereto. An O-ring seal 118 is disposed within the annular groove formed in the periphery of the pistonhead structure by the flange 114 of the head member 112 and the flange portion 108. The O-ring seal 118 engages the inner periphery of the cylindrical pressure chamber 38.

The pistonhead structure 106 is thus slidably mounted within the chamber 38. The outer end portion of the chamber 38 is adapted to receive fluid under pressure from the reservoir 44 under the control of a trigger valve mechanism, generally indicated at 120, to effect a longitudinal movement of the driving chamber assembly 22 in a direction toward the drive track means 14 by the fluid under pressure from the reservoir. During this movement the essential pressure conditions are established within the driving chamber acting on the piston. To this end, the outer end of the chamber 38 is closed by a cap assembly, generally indicated aT 122.

The cap assembly includes an inner member 124 having a plurality of circumferentially spaced ports 126 formed therein, as best shown in FIG. 10. The outer ends of the ports 126 are interconnected by an arcuate groove 128 formed in the outer surface of the inner cap member 124, the groove 128 having an end portion 130 which communicates with the outer end of a port 132.

The cap assembly 122 also includes an outer cap member 134 which, together with the inner cap member 124 and appropriate gaskets 136 and 138, are secured to the adjacent head portion 34 of the housing 12, as by a plurality of circumferentially spaced bolts 140 extending through the cap members and gaskets and threadedly engaged within appropriate bosses formed on the housing. The outer cap member 134 closes the outer side of groove portions 128 and 130 so as to provide a passage from the ports 126 to the port 132. The inner end of the inlet port 132 is disposed in communication with the outer end of a longitudinally extending passage 142 formed in the housing 12. As best shown in FIG. 9, the inner end of the passage 142 communicates with a laterally extending port 144 which is selectively communicated with the reservoir 44 and the exhaust chambers 36 and 48 under the control of the trigger valve mechanism 120.

The port 144 communicates laterally with the central portion of a bore 146 formed in the handle portion 42 of the housing 12 in a position adjacent the head portion 34. The outer end of the bore 146 communicates with the exterior of the handle portion 42 and the inner end thereof communicates with the reservoir 44 through a central axial opening 148, under the control of trigger valve mechanism 120.

The trigger valve mechanism 120 may be of any desired construction and, as shown in FIGS. 1--3, includes a tubular valve insert 150 disposed within the bore 146 and having three O-ring seals mounted within appropriate annular grooves formed in the exterior periphery thereof at longitudinally spaced positions. The two innermost seals engage the interior periphery of the bore 146 at opposite sides of the port 144 and a plurality of openings 152 extend through the tubular insert 150 so as to communicate the port 144 with the interior of the insert, as shown in FIG. 9. Formed within the interior of the insert on opposite sides of the openings 152 are a pair of oppositely facing frustoconical valve seats 154 and 156 adapted to be alternately engaged by a pair of frustoconical valve elements 158 and 160, respectively, formed of a rubberlike material. The valve elements are mounted on a valve stem 162, the outer end of which is provided with an outwardly extending pistonlike flange 164 slidably sealingly mounted, as by a suitable O-ring or the like, within the outer cylindrical interior portion of the valve insert. The cylindrical portion has a plurality of circumferentially spaced cylindrical openings 166 extending radially therethrough to communicate the interior of the valve insert with an exhaust passage 168 formed in the handle portion of the housing 12 and communicating at one end with the exhaust chamber 36 of the head portion 34 and at its other end with the exhaust chamber 48 of the handle portion of the housing 12.

The valve mechanism 120 operates in conventional fashion and is normally disposed in an inoperative position, as shown in FIGS. 1 and 3, wherein the valve element 160 is out of engagement with the seat 156 and the valve element 158 is in engagement with the valve seat 154 thus communicating the outer end of the chamber 38 with the atmosphere through exhaust chambers 36 and 48, passage 168, openings 166 and 152, port 144, passage 142, port 132, annular groove 128 and ports 126.

It will be noted that the inner end of the valve stem 162 and the valve element 158 are in communication with the fluid under pressure within the reservoir chamber 44 by the opening 148, which fluid pressure serves to bias the valve mechanism into its normal inoperative position. When the valve stem 162 is moved into an operative position, valve element 158 moves away from its valve seat 154 and valve element 160 engages its valve seat 156 thus communicating the reservoir pressure with the outer end of the pressure chamber 38 and closing off the communication of the latter with the atmosphere.

When reservoir pressure is communicated with the outer end of the chamber, the pistonhead structure 106 carried by the driving chamber assembly 22 is acted upon to move the latter with respect to driving piston 20, since the latter is retained against movement by the latch pin 66. This movement of the driving chamber assembly 22 establishes a desired pressure condition above reservoir pressure which acts upon one side of the driving piston during its driving stroke.

Preferably, this movement of the driving chamber assembly 22 is also utilized to establish a negative pressure condition on the opposite side of the driving piston. To this end, closure means, in the form of a radially inwardly extending end wall 170 on the member 56, is provided as a part of the driving chamber assembly 22 at the end thereof opposite the pistonhead structure 106. The end wall 170 is centrally apertured to receive the fastener driving element therethrough and an O-ring seal 172 is mounted within the aperture for slidable sealing engagement with the periphery of the fastener driving element.

It will be understood that while it is preferable to establish both a higher than line driving pressure and a negative driving pressure for effecting movement of the fastener driving element through its driving stroke, it is within the contemplation of the present invention to utilize either of these increased energy conditions. For example, rather than to provide a pressure tight closure means, such as the sealed end wall 170, the adjacent end of the cylinder 24 could simply be slightly opened so as to communicate with the exhaust chamber 36. Such an arrangement may be desirable since it would have the effect of providing a slight air cushion for absorbing the shock of the fastener driving element 18 when it completes its driving stroke. Moreover, a negativepressure condition may be established while maintaining reservoir or line pressure within the driving chamber 58. This would entail simply providing for open communication between the outer end portion of the pressure chamber 38 and the driving chamber 58.

The valve mechanism 120 is moved from its normal inoperative position into its operative position by the contact trip-trigger interlock mechanism 30. As best shown in FIGS. 1--3, the housing 12 at the juncture between the head portion 34 and handle portion 42 is formed with a recess 176 within which a trigger housing section 178 is mounted. The housing section 178 is retained within the recess by any suitable means, such as a bolt 180 extending through the housing section and threadedly engaged within the adjacent handle portion 42.

The central portion of the trigger housing section 178 is formed with a recess 182 which is open at one end in communication with the bore 146 of the trigger valve mechanism 120 and at its opposite end with a transversely extending finger receiving opening 184. Disposed within the recess 182 adjacent the trigger valve mechanism 120 is a generally inverted T-shaped interlock element 186 having an enlarged central portion provided with a transversely elongated slot 188. The interlock element 186 is mounted within the recess 182 by means of a pivot pin 190 carried by the housing section and extending within the recess through the elongated slot 188. A trigger member 192 is disposed adjacent the interlock element 186 and is mounted within the trigger housing section 178 for limited pivotal movement, as by pivot pin 194, between operative and inoperative positions. The central portion of the trigger member is shaped to be engaged by the finger of the operator and has a pair of flanges 196 extending outwardly from opposite sides thereof which are adapted to engage the adjacent wall of the finger receiving opening 184 when the trigger member has been moved into its operative position.

The end of the trigger member opposite from the pivot pin 194 is preferably provided with an adjustable element 198 which is adapted to abuttingly engage the adjacent end of the interlock element 186. The opposite end of the interlock member 186 is adapted to be abuttingly engaged by a transversely extending element 200 mounted for longitudinal reciprocating movement within a transversely extending opening 202 formed in the adjacent portion of the trigger housing section 178. The ends of the element 200 extend outwardly of the opening 202 and are fixedly connected to the ends of a pair of transversely spaced parallel strut elements 204. The opposite ends of the strut elements are fixedly connected with a longitudinally extending contact trip element 206 mounted on the magazine assembly 16 for longitudinal reciprocation at a position adjacent the drive track 14.

The contact trip element 206 includes an outer end surface 208 which is adapted to engage the workpiece within which a fastener F is to be driven. As best shown in FIG. 1, the work contacting surface 208 of the element 206 is normally disposed in spaced relation to an adjacent work contacting surface 210 of the magazine assembly disposed adjacent the outer end of the drive track 14. The contact trip element 206 is moved from its normally inoperative position to an operative position when the apparatus 10 is manually moved into contact with the workpiece within which a fastener is to be driven. During this movement the surface 208 will initially engage the surface of the workpiece and the interlock actuating element 200 will be moved into abutting engagement with the interlock element 186 until the surface 210 contacts the workpiece. Movement of the element 200 into engagement with the end of the interlock element 186 will effect a tilting movement of the latter into the position shown in FIG. 3.

It will be noted that this movement of the interlock member 186 is not sufficient to effect a movement of the trigger valve mechanism 120. However, when the interlock element 186 is disposed in this position, movement of the trigger member 192 from its inoperative position, as shown in FIG. 3, to its operative position, as shown in FIG. 2, will effect movement of the interlock element through the abutting engagement of the adjusting element 198 therewith sufficient to move the valve stem 162 from its inoperative position, as shown in FIGS. 1 and 3, to its operative position, as shown in FIG. 2. The contact trip-trigger interlock mechanism 30 is thus operable to move the trigger valve mechanism 120 from its inoperative position to its operative position only when the apparatus 10 has been moved into operative contact with the workpiece piece into which the fastener is to be driven and the trigger member 192 has been manually actuated by the operator. However, the trigger valve mechanism 120 will be moved from its operative position into its inoperative position in response to the movement of either the trip contact 206 into its operative position or the trigger member 192 into its inoperative position. In this way, the contact trip-trigger interlock mechanism 30 is capable of permitting "drag" firing wherein the apparatus is maintained in contact with the workpiece while being dragged or moved therealong in conjunction with repeated manual actuation of the trigger member 192, or "bump" firing wherein the operator continually maintains the trigger member 192 in its operative position and the apparatus is repeatedly moved into and out of engagement with the workpiece at spaced positions therealong.

The fluid pressure operated means 32 for effecting the return stroke of the fastener driving element 18 is operable in response to the movement of the trigger valve mechanism 120 from its operative position to its inoperative position after the fastener driving element 18 has been moved through its driving stroke, as shown in FIG. 3. The return means 32 preferably includes a proportioning valve mechanism, generally indicated at 212. As best shown in FIG. 4, proportioning valve mechanism 212 is mounted within a cylindrical recess 214 formed in the outer end of the head portion 34 in parallel relation to the main pressure chamber 38. The inner end of the recess 214 communicates with one end of a longitudinal passage 216, the opposite end of which communicates with the inner end portion of the pressure chamber 38, as by a transversely extending opening 218. The inner end portion of the pressure chamber 38 is sealed, as by an O-ring 219, mounted within an appropriate groove in the flange portion 40 and slidably sealingly engaging the exterior periphery of the cylindrical member 56.

The valve mechanism 212 includes a differential piston valve member 220 mounted within the recess 214 and including a large piston portion 222 having an appropriate O-ring seal or the like mounted in the exterior periphery thereof for engaging the interior periphery of the recess 214, and a small piston portion 224 adjacent the outer end thereof also having an appropriaTe O-ring seal or the like mounted in the outer periphery thereof. The small piston portion 224 is disposed in slidable sealing engagement with the interior periphery of a centrally apertured exteriorly flanged insert 226 mounted in the outer end of the recess 214 and sealingly engaged therein, as by an O-ring seal or the like.

The valve member 220 has an opening extending longitudinally therethrough providing an intermediate frustoconical shoulder 228. Mounted within the valve member 220 in sealing engagement with the shoulder 228 is a conventional tire valve 230. The tire valve 230 includes the usual valve stem 232 which extends outwardly of the valve member 220 adjacent the inner end of the recess 214. Disposed within the inner end of the recess 214 is an apertured valve stem engaging plate 234 having a series of circumferentially spaced openings extending longitudinally therethrough, the outer ends of the openings being intercommunicated by a circular groove. The portion of the recess 214 between insert 226 and the large piston portion of the valve member 220 is exhausted to atmosphere as by a port 236 formed in the adjacent portion of the housing 12.

The small piston portion 224 of the valve member 220 is communicated at all times with the fluid pressure within the reservoir 44 through a port 238 extending longitudinally through the inner cap member 124 with its inner end in communication with the outer end of the recess 214, and its outer end in communication with one end of a generally L-shaped groove 240 formed in the outer end of the inner cap member 124. As best shown in FIG. 10, the central portion of the groove 240 communicates with one end of a port 242 formed in the inner cap member, the opposite end of which communicates with the adjacent end of a longitudinal passage 244 formed in the head portion of the housing 12 in parallel relation to the passage 142. As best shown in FIG. 8, the opposite end of the passage 244 is communicated with the reservoir chamber 44, as by a lateral port 246.

The opposite end of the groove 240 communicates with a central recess 248 formed in the interior of the outer cap member 134 and an aligned bore 250 formed in the inner cap member 124. The recess 248 constitutes a chamber which is at all times communicated with the reservoir chamber 44 so as to provide a source of fluid under reservoir or line pressure from which the driving chamber 58 of the driving chamber assembly 22 is charged with reservoir or line pressure under the control of a pair of cooperating valve mechanisms 252 and 254 carried respectively by the inner cap member 124 and the piston member 112 of the driving chamber assembly 22. The valve mechanism 252 includes a tubular valve insert 256 sealingly mounted within the bore 250, as by an O-ring seal and a snapring or the like. The tubular valve insert 256 has a central bore 258 extending therethrough formed with a counterbore in the outer end thereof defining an intermediate outwardly facing valve seat 260. Mounted within the counterbore is a ball valve 262 which is resiliently urged into engagement with the valve seat 260, as by a coil spring 264.

The valve mechanism 254 includes a hollow member 266 having a stemlike outer portion and a flanged cylindrical inner portion disposed in a correspondingly shaped central opening formed in the piston member 112 and sealingly secured therein, as by an O-ring seal and a snapring or the like. The stemlike outer portion of the member 266 is of an exterior size to sealingly engage within the bore 258 of the valve insert 256, as by an O-ring seal or the like. The extremity of the stem portion of the member 266 is adapted to engage and unseat the ball valve 262 and has formed therein a transversely extending slot 268 which serves to communicate the adjacent end of the member 266 with the recess 248. The opposite end of the member 266 communicates with the chamber 58 under the control of a flap valve 270 carried by the piston member 112 in operative relation to the adjacent end of the member 266.

It will be understood that appropriate bumper means of an appropriate resilient material is preferably provided for absorbing shocks incident to the movement of the various parts of the apparatus into their limiting positions. To this end, a rubber bumper ring 272 is mounted within an appropriate annular recess formed in the inner surface of the inner cap member 124 for engaging the piston member 112 when the driving chamber assembly 22 is disposed in its inoperative position. An annular rubber bumper 274 is disposed within the end of the cylinder 24 between the end wall 170 and the driving piston 20 and a further annular rubber bumper 276 is disposed within the exhaust chamber 36 in engagement with the housing section 52.

OPERATION

When the apparatus 10 is connected with a source of fluid under pressure, the fluid under pressure will enter the reservoir chamber 44 causing the trigger valve mechanism 120 to be biased into its inoperative position, as shown in FIG. 1. Fluid under pressure from the reservoir flows through lateral port 246, longitudinal passage 244 (FIG. 8), aligned port 242, groove 240, port 238, and the recess 248 (FIG. 10). Fluid pressure in the port 238 acts on the small piston portion 224 of the valve member 220 of the proportioning valve mechanism 212 to move the latter from its normal position, as shown in FIGS. 1--3 to its operative position, as shown in FIG. 4. During the movement of the valve member 220 into its operative position, valve stem 232 of the tire valve 230 will engage the plate 234 so as to open the tire valve permitting fluid under pressure from the port 238 to pass through the valve member 220 past the tire valve into the inner end of the recess 214. From the recess fluid under pressure flows through the apertures in plate 234 into longitudinal passage 216 and then through port 218 into the inner end portion of the pressure chamber 38, so as to bias the driving chamber assembly 22 into its inoperative position shown in FIG. 1.

The pressure within the inner portion of the recess 214 acts upon one side of the large piston portion 222 which has a substantially greater effective area than the effective area of the small piston portion 224. Since the opposite side of the large piston portion is exposed to atmosphere by port 236, when the pressure within the inner end of the recess 214 reaches a value substantially less than full line pressure, the valve member 220 will be moved from its operative position, as shown in FIG. 4 into its normal inoperative position, as shown in FIGS. 1--3, during which movement tire valve 230 closes. Preferably, the relationship between the effective pressure areas of the large and small piston portions of the valve 220 are such that the proportioning valve mechanism 212 will maintain a pressure of approximately 10 percent of line pressure within the chamber 38 when the driving chamber assembly 22 is disposed in its inoperative position, as shown in FIG. 1.

With the driving chamber assembly 22 disposed in its first or inoperative position, the stem portion of the valve member 266 will be disposed within the bore 258 of the valve insert 256 and the extremity of the stem portion will maintain the ball valve 262 away from its seat 260 so that the slot 268 will serve to communicate the pressure within the recess 248 with the interior of valve member 266. Consequently, fluid pressure within the valve member 266 flows past the flap valve 270 and into the driving chamber 58 until it attains full reservoir or line pressure.

Under normal operating conditions, valve mechanisms 212, 252, and 254 are operable only when the source of pressure is connected with the apparatus in the manner set forth above. It will be noted that the parts of the apparatus are disposed in the position shown in FIG. 1 after initial connection with the source of fluid under pressure.

When both the contact trip element 206 and the trigger member 192 are moved into their operative positions, as shown in FIG. 2, the trigger valve mechanism 120 will be moved from its normally inoperative position into its operative position, in the manner previously set forth in detail. The movement of the trigger valve mechanism 120 into its operative position communicates fluid under pressure from the reservoir chamber 44 with the outer end portion of the pressure chamber 38 and this pressure acts to move driving chamber assembly 22 longitudinally in a direction toward the drive track 14. During the initial portion of this movement, the valve mechanism 254 moves away from the value mechanism 252, the engagement of the ball valve 262 with its seat 260 serving to prevent communication between the reservoir fluid pressure within the recess 248 and the fluid pressure within the outer end portion of the pressure chamber 38. Also, during the initial portion of this movement, the semispherical end 94 of the fastener driving element 18 will engage the latch pin 66 in latching relation as shown in FIG. 6 so that during the subsequent movement of the driving chamber assembly 22, cylinder 24 will move longitudinally with respect to the driving piston 20. This relative movement serves to establish a pressure condition within the driving chamber 58 which increases during the movement of the driving chamber assembly 22 from a value substantially equal to reservoir or line pressure to a value substantially above reservoir or line pressure (as, for example, from 80 p.s.i. to 200 p.s.i. and above). In this regard, it will be noted that the effective pressure area of the piston assembly 106 is considerably greater than the effective pressure area of the piston 20. Also, during the above-mentioned relative movement a negative pressure condition is established within the cylinder 24 between the end wall 170 and the piston 20 which decreases during the movement.

Depending upon the adjusted position of the cam roller 96, the surface 104 will engage the cam roller at a predetermined position, as shown in FIG. 2, between the first or inoperative position of the driving chamber assembly 22, as shown in FIG. 1, and the second or operative position, as shown in FIG. 3. The engagement of the surface 104 with the cam roller 96 serves to tilt the entire driving chamber assembly 22 which, in turn, causes a lateral movement of the end 94 of the fastener driving element 18 from its latched relation, as shown in FIG. 6, to a releasing position, as shown in FIG. 7. During this movement it will be noted that the axis of the end 94 of the fastener driving element is effectively moved over center with respect to the axis of the latch pin 66, so that the transverse component of the longitudinally outward force of the fastener driving element acting on the latch pin shifts from a direction tending to move the latch pin toward the right, as shown in FIG. 6, to a direction tending to move the latch pin to the left, as shown in FIG. 7. While movement of the latch pin to the right is prevented by the adjustable abutment 84, movement to the left is permitted through the yielding action of the spring pressed member 78. Consequently, as soon as the fastener driving element 18 is moved into its releasing position, as shown in FIG. 7, the fastener driving element will then begin to move longitudinally through its driving stoke during which it initially engages the fastener F disposed within the drive track and then moves the fastener outwardly and into the workpiece, as shown in FIG. 3.

It is important to note that the driving stroke is initiated under the combined action of the fluid under pressure within the driving chamber 58 which is higher than the reservoir or line pressure and the negative pressure established within the cylinder between the piston 20 and the end wall 170. While these pressure conditions which are established by the movement of the driving chamber assembly 22 into the position shown in FIG. 2 will reduce during the driving stroke of the fastener driving element 18, even at the end of the driving stroke, as shown in FIG. 3, the driving piston 20 will still have at least line or reservoir pressure acting thereon.

During the movement of the driving chamber assembly 22 from its first position, as shown in FIG. 1, to its second position, as shown in FIG. 3, the fluid within the inner end portion of the pressure chamber 38 and the passage 216 will increase from a value which is substantially 10 percent of line pressure, as determined by the proportioning valve mechanism 212, to a substantially greater pressure which preferably may be substantially equal to reservoir or line pressure. It will also be noted that this pressure has no effect whatsoever on the movement of the fastener driving element through its driving stroke.

After the driving stroke has been accomplished, and the trigger valve mechanism 120 has been moved back into its inoperative position by the operation of the contact trip-trigger interlock mechanism 30 in the manner described above in detail, fluid under reservoir or line pressure within the outer portion of the pressure chamber 38 is allowed to exhaust through the port 168. Since this pressure is exhausted, the pressure within the inner end portion of the pressure chamber 38 acts to effect movement of the driving chamber assembly 22 from its second position, as shown in FIG. 3, back into its first position. During this movement the fastener driving element 18 is moved through its return stroke by the engagement of the driving chamber assembly 22 therewith.

It will be noted that by exhausting the fluid under reservoir or line pressure within the pressure chamber 38 through the exhaust chamber 36, the tendency for air to be drawn into the exhaust chamber is eliminated and, in fact, a flow of air through the exhaust chamber 36 and out of the guide track 14 will take place which serves not only to maintain proper lubrication of the associated parts, but to prevent foreign material from being drawn into the same.

It will also be noted that in conjunction with the favorable utilization of the energy available to effect the driving stroke achieved by the present invention, the construction is such that the size and weight of the device is maintained at an acceptable level. Moreover, the device has the operational advantage of high velocity movement of the driving piston in its driving stroke as well as fast cycling, and where negative pressure conditions are established on the driving element side of the driving piston, a particularly quiet operation is achieved, by virtue of the elimination of the necessity of displacing and discharging air during the driving stroke. Furthermore, the very favorable ratio of the moving mass of the device (the driving piston and the driving element) to the static mass thereof (the remaining structure) materially reduces, if not substantially eliminates, recoil at the end of the driving stroke. The securement of a substantially recoilless operation is enhanced because the driving piston is contained within a movable cylinder.

It thus will be seen that the objects of this invention have been fully and effectively accomplished. It will be realized, however, that the foregoing specific embodiment has been shown and described only for the purpose of illustrating the principles of this invention and is subject to extensive change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.

Claims

I claim:

1. Fastener driving apparatus comprising means defining a housing, reservoir means within said housing for receiving and containing fluid under pressure supplied thereto from a source of fluid under pressure, drive track means carried by said housing for receiving successive fasteners to be driven from a supply of such fasteners fed thereto, fastener driving means carried by said housing for movement from a fastener receiving position through said drive track means into a fastener driven position to drive a fastener in said drive track means into a workpiece and from said fastener driven position back into said fastener receiving position, means within said housing defining a driving pressure chamber disposed in fluid pressure communicating relation to said fastener driving means, and means operable by fluid under pressure from said reservoir for establishing a driving fluid pressure higher than said reservoir fluid pressure within said driving chamber acting on said fastener driving means with said fastener driving means in said fastener receiving position and for effecting movement of said fastener driving means from said fastener receiving position to said fastener driven position under the action of said higher driving pressure.

2. Fastener driving apparatus comprising means defining a housing, reservoir means within said housing for receiving and containing fluid under pressure supplied thereto from a source of fluid under pressure, drive track means carried by said housing for receiving successive fasteners to be driven from a supply of such fasteners fed thereto, fastener driving means carried by said housing for movement from a fastener receiving position through said drive track means into a fastener driven position a fastener in said drive track means into a workpiece and from said fastener driven position back into said fastener receiving position, means within said housing defining a driving pressure chamber disposed in fluid pressure communicating relation to said fastener driving means, and means operable by fluid under pressure from said reservoir for establishing a positive driving fluid pressure and a negative driving fluid pressure within said driving chamber acting on said fastener driving means with said fastener driving means in said fastener receiving position and for effecting movement of said fastener driving means from said fastener receiving position to said fastener driven position under the action of said positive and negative driving pressures.

3. Fastener driving apparatus as defined in claim 2 wherein said positive driving fluid pressure is higher than said reservoir fluid pressure.

4. Fastener driving apparatus comprising means defining a housing, reservoir means within said housing for receiving and containing fluid under pressure supplied thereto from a source of fluid under pressure, drive track means carried by said housing for receiving successive fasteners to be driven from a supply of such fasteners fed thereto, means within said housing defining a driving chamber including a cylinder, a driving piston reciprocably mounted within said cylinder, a fastener driving member operatively connected with said driving piston for movement therewith in a driving g stroke from a fastener receiving position through said drive track means into a fastener driven position to drive a fastener in said drive track means into a workpiece and in a return stroke from said fastener driven position into said fastener receiving position means operable by fluid under pressure from said reservoir means for establishing a driving fluid pressure higher than said reservoir fluid pressure within said driving chamber acting on said driving piston with said fastener driving member in said fastener receiving position in a direction to move said fastener driving member through said driving stroke, and means for retaining said fastener driving member in said fastener receiving position during the establishment of said higher driving fluid pressure and for releasing the same after the establishment of said higher driving pressure to thereby permit the movement of said driving piston under the action of said higher driving pressure and hence the movement of said fastener driving means through said driving stroke.

5. Fastener driving apparatus as defined in claim 4 wherein said higher pressure establishing means comprises pistonhead means of a size greater than said driving piston operatively connected with said cylinder, means within said housing defining with one side of said pistonhead means a pressure chamber including a cylindrical surface receiving said pistonhead means for longitudinal sliding movement therein between first and second positions, and valve means carried by said housing operable to communicate said pressure chamber with the fluid under pressure within said reservoir means to move said pistonhead means from said first position to said second position to thereby establish said higher drive fluid pressure within said driving chamber.

6. Fastener driving apparatus as defined in claim 5 including a work contacting member carried by said housing for movement from an inoperative position to an operative position in response to the movement of said apparatus into cooperating engagement with a workpiece, a trigger member carried by said housing for manual movement from an inoperative position to an operative position, and interlock means for operating said valve means in response (1) to the simultaneous movement of said work contacting and said trigger members into their operative positions. (2) to the movement of said work contacting member into its operative position when said trigger member is in its operative position when said trigger member is in its operative position or (3) to the movement of said trigger member into its operative position when said work contacting member is in its operative position.

7. Fastener driving apparatus as defined in claim 6 wherein said interlock means comprises an elongated interlock member having a transversely extending slot formed in the central portion thereof, a pivot pin carried by said housing disposed within said slot, means connecting one end of said interlock member with said work contacting member for movement thereby in response to the movement of said work contacting member from said inoperative position to said operative position, means for connecting the other end of said interlock member with said trigger for movement in response to the movement of said trigger member from said inoperative position to said operative position, said interlock member including a valve means engaging portion intermediate the ends thereof.

8. Fastener driving apparatus as defined in claim 5 including means within said housing defining an exhaust chamber between said pressure chamber and said drive track means for receiving said cylinder when said pistonhead means is disposed in said second position, said valve means being operable to communicate said pressure chamber with said exhaust chamber and said drive track means communicating therewith during the movement of said pistonhead means from said second position to said first position.

9. Fastener driving apparatus as defined in claim 5 wherein said valve means is operable to communicate said pressure chamber with the atmosphere during the movement of said pistonhead means from said second position to said first position, means defining a return chamber communicating with said cylindrical surface and the opposite side of said pistonhead means with an effective area substantially less than the effective area of said one side of said pistonhead means communicating with said pressure chamber, and means for communicating fluid under pressure from said reservoir to said return chamber for effecting movement of said pistonhead means from said second position to said first position in response to the operation of said valve means to communicate said pressure chamber with the atmosphere.

10. Fastener driving apparatus as defined in claim 9 wherein said last-mentioned means comprises a valve operatively connected between said return chamber and said reservoir means for maintaining a fluid pressure within said return chamber when said pistonhead means is in said first position which is not in excess of substantially less than said reservoir fluid pressure so that said substantially lesser fluid pressure will be compressed during the movement of said pistonhead means from said first position to said second position.

11. Fastener driving apparatus as defined in claim 5 wherein said fastener driving member is circular in cross-sectional configuration, closure means movable with said cylinder and extending inwardly therefrom and slidably sealingly engaging the exterior periphery of said fastener driving member, the interior periphery of said cylinder and the exterior periphery of said fastener driving member extending between said driving piston and said closure means defining a pressure tight chamber which is expansible in response to the movement of said pistonhead means from said first position onto said second position with said fastener driving member in said fastener receiving position to thereby establish in said pressure tight chamber a negative fluid pressure when said pistonhead means is disposed in said second position and said fastener driving member is disposed in said fastener receiving position.

12. Fastener driving apparatus as defined in claim 5 wherein said fastener driving member includes a generally semispherical driving end and wherein said retaining and releasing means comprises a cylindrical latch member mounted for transverse movement between latching and releasing positions, said latch member in said latching position being disposed with its axis spaced transversely from the axis of the semispherical driving end of said fastener driving member between the latter and said drive track means.

13. Fastener driving apparatus as defined in claim 12 wherein the driving end of said fastener driving member is mounted for limited transverse movement when said fastener driving member is disposed in said fastener receiving position from a latched position wherein its axis is disposed in said spaced transverse relation from the axis of said latch member so as to bias said latch member for transverse movement in one direction and a latch releasing position wherein the axis of said fastener driving member is disposed in transversely spaced relation from the axis of said latch member so as to bias said latch member transversely in the opposite direction, stop means for limiting the transverse movement of said latch member in said one direction when said latch member is disposed in said latching position, resilient means permitting yielding transverse movement of said latch member in said opposite direction out of said latching position toward said releasing position and means operable in response to the movement of said pistonhead means into a predetermined position to said second position for effecting a transverse movement of the driving end of said fastener driving member from said latched position to said latch releasing position.

14. Fastener driving apparatus as defined in claim 13 wherein said last-mentioned means comprises cam roller means carried by said housing in a position to be engaged by said driving chamber defining means when its piston head means is moved into said predetermined position so that said driving chamber and the fastener driving element associated therewith will be tilted to effect the transverse movement of the driving end of said fastener driving element from said latched position to said latch releasing position.

15. Fastener driving apparatus as defined in claim 14 wherein said cam roller means includes a cam roller and means for mounting said cam roller in said housing in any one of a plurality of longitudinally spaced positions.

16. Fastener driving apparatus as defined in claim 5 including first check valve means carried by said pistonhead means for permitting flow of fluid under pressure from said reservoir means into said driving chamber when said pistonhead means is disposed in said first position and for preventing flow of fluid under pressure outwardly of said driving chamber when said pistonhead means is disposed out of said first position and cooperating second check valve means carried by said housing for communicating fluid under pressure from said reservoir means to said first check valve means when said pistonhead means is disposed in said first position and for preventing flow therethrough from said reservoir means to said pressure chamber during the movement of said pistonhead means from said second position into said first position.

17. Fastener driving apparatus comprising means defining a housing, reservoir means within said housing for receiving and containing fluid under pressure supplied thereto from a source of fluid under pressure, drive track means carried by said housing for receiving successive fasteners to be driven from a supply of such fasteners fed thereto, means within said housing defining a driving chamber including a cylinder, a driving piston reciprocably mounted within said cylinder, a fastener driving member operatively connected with said driving piston for movement therewith in a driving stroke from a fastener receiving position through said drive track means into a fastener driven position to drive a fastener in said drive track means into a workpiece and in a return stroke from said fastener driven position into said fastener receiving position, means operable by fluid under pressure from said reservoir means for establishing a positive driving fluid pressure and a negative driving fluid pressure within said driving chamber acting on said driving piston with said fastener driving member in said fastener receiving position in a direction to move said fastener driving member through said driving stroke, and means for retaining said fastener driving member in said fastener receiving position during the establishment of said positive and negative driving fluid pressures and for releasing the same after the establishment of said positive and negative driving pressures to thereby permit the movement of said driving piston under the action of said positive and negative driving pressures and hence the movement of said fastener driving means through said driving stroke.

18. Fastener driving apparatus as defined in claim 17 wherein said positive and negative pressure establishing means comprises pistonhead means of an exterior diameter size greater than the exterior diameter size of said driving piston operatively connected with said cylinder, means defining with one side of said pistonhead means a pressure chamber including a cylindrical surface receiving said pistonhead means for longitudinal sliding movement therein between first and second positions, closure means movable with said cylinder and extending inwardly therefrom and slidably sealingly engaging the exterior periphery of said fastener driving member, the interior periphery of said cylinder and the exterior periphery of said fastener driving member extending between said driving piston and said closure means defining a pressure tight chamber which is expansible in response to the movement of said pistonhead means from said first position to said second position with said fastener driving member in said fastener receiving position to thereby establish in said pressure tight chamber a negative fluid pressure when said pistonhead means is disposed in said second position and said fastener driving member is disposed in said fastener receiving position, and valve means carried by said housing operable to communicate said pressure chamber with the fluid under pressure within said reservoir means to move said pistonhead means from said first position to said second position.

19. Fastener driving apparatus as defined in claim 18 wherein said fastener driving member includes a generally semispherical driving end and wherein said retaining and releasing means comprises a cylindrical latch member mounted for transverse movement between latching and releasing positions, said latch member in said latching position being disposed with its axis spaced transversely from the axis of the semispherical driving end of said fastener driving member between the latter and said drive track means.

20. A fastener driving apparatus as defined in claim 19 wherein the driving end of said fastener driving member is mounted for limited transverse movement when said fastener driving member is disposed in said fastener receiving position from a latched position wherein its axis is disposed in said spaced transverse relation from the axis of said latch member so as to bias said latch member for transverse movement in one direction and a latch releasing position wherein the axis of said fastener driving member is disposed in transversely spaced relation from the axis of said latch member so as to bias said latch member transversely in the opposite direction, stop means for limiting the transverse movement of said latch member in said one direction when said latch member is disposed in said latching position, resilient means permitting yielding transverse movement of said latch member in said opposite direction out of said latching position toward said releasing position and means operable in response to the movement of said pistonhead means into a predetermined position during its movement from said first position to said second position for effecting a transverse movement of the driving end of said fastener driving member from said latched position to said latch releasing position.

21. In a fastener driving apparatus of the type including a housing, fluid pressure operated fastener driving means carried by said housing for movement through a fastener driving stroke and a return stroke, valve means carried by said housing for movement from a normally inoperative position into an operative position for effecting the operation of said fluid pressure operated means through said fastener driving stroke, a work contacting member carried by said housing for movement, from an inoperative position to an operative position in response to the movement of said apparatus into cooperating engagement with a workpiece, a trigger member carried by said housing for manual movement from an inoperative position to an operative position, and interlock means for effecting movement of said valve means into the operative position thereof in response (1) to the simultaneous movement of said work contacting and said trigger members into their operative positions, (2) to the movement of said work contacting member into its operative position when said trigger member is in its operative position or (3) to the movement of said trigger member into its operative position when said work contacting member is in its operative position, the improvement which comprises said interlock means including an elongated interlock member having a transversely extending slot formed in the central portion thereof, a pivot pin carried by said housing disposed within said slot, means connecting one end of said interlock member with said work contacting member for movement thereby in response to the movement of said work contacting member from said inoperative position to said operative position, means for connecting the other end of said interlock member with said trigger for movement in response to the movement of said trigger member from said inoperative position to said operative position, said interlock member including a valve means engaging portion intermediate the ends thereof.