Fastener Driving Tool

Abstract

A high pressure stud gun or fastener driving tool includes a housing providing a cylinder, a combustion chamber, and a drive track to which studs or fasteners to be driven are supplied. A piston movable in the cylinder actuates a driver slidable in the drive track. A fluid controlled main valve is normally biased by compressed air supplied to a large area valve piston surface to close communication between the combustion chamber and the cylinder. A control assembly on a housing handle supplies a metered charge of combustible material to the chamber and initiates combustion thereof. A small area valve piston surface communicating with the combustion chamber opens the main valve when the gas resulting from combustion reaches a relatively high pressure, and this gas then enters the cylinder to actuate the fastener driver through a power stroke. The control assembly also includes valving for opening and closing the main valve and for purging the combustion chamber and the cylinder of combustion products. The pressure of the compressed air supplied to the large area valve piston surface controls the pressure of the gas admitted to the cylinder, and adjustable regulators on the compressed air source control the driving force applied.

Description

This invention relates to a fastener driving tool and, more particularly, to a high pressure tool capable of driving fasteners into such hard and dense material as steel or concrete.

Most high power tools for driving or setting fasteners such as studs in hard or dense material use a powder or propellant charge that generates gases directly admitted to a piston-cylinder motor. This means that the rate of combustion of the gases controls the driving force available at any given time during combustion with the result that there tend to be differences in the energy imparted to fasteners on different operations. Further, control over the power desired in any given operation is achieved by using different powder charges with the result that only a rather coarse adjustment of power can be effected. In addition, the cost of the discrete powder charges required for each operation of the tool is somewhat greater than desirable.

Accordingly, one object of the present invention is to provide a new and improved high power tool for driving fasteners.

Another object is to provide a new and improved single stroke power unit of the type using a piston-cylinder motor having a gas generating chamber and a valve controlled by the generated gas for controlling the admission of the generated gas to the cylinder.

A further object is to provide a new and improved single stroke power tool using a combustible fuel for driving a cylinder-piston motor.

A further object is to provide a power unit for a fastener driver using a cylinder-piston motor wherein a biased main valve seals off communication between the cylinder and the compression chamber until the pressure of the combustion products exceeds the main valve bias, following which the combustion products are supplied to the cylinder to operate the motor.

A further object is to provide a single stroke fastener driving tool using a pneumatically biased main valve subjected to the pressure of gas generated in the combustion chamber to control the admission of combustion products from the chamber to a cylinder and wherein the pneumatic bias can be regulated to control the pressure at which combustion products are admitted to the cylinder.

A further object is to provide a fastener driving tool using a combustion chamber to generate piston driving gases and having a new and improved control assembly for supplying combustible material to the chamber and controlling the sequence of operation of the tool.

In accordance with these and many other objects, an embodiment of the tool having a housing having a generally vertically extending head portion and a rearwardly extending handle portion. The head portion defines a combustion chamber, a cylinder in which is slidably mounted a piston connected to a driver element, and a fastener receiving structure in which the fastener driver is movable. Communication between the combustion chamber and the cylinder is normally closed by a main valve having an actuating differential piston with a small area exposed to the combustion chamber and a large area supplied with compressed air. A control valve assembly on or in the handle includes a multiposition valve operable to different settings to effect a sequence of operation of the tool.

In one setting, the main valve is open and compressed air is supplied through the combustion chamber and the cylinder to purge these elements of prior combustion products. In another setting, the large area surface on the piston for the main valve is supplied with compressed air to close the main valve, and a metered charge of a combustible material such as propane gas is supplied into the combustion chamber. In a further setting, the metered charge of combustible gas is supplied with compressed air to provide a combustible mixture. Operation of an electric switch or other control renders an ignition means such as a spark plug or a glow plug effective to effect combustion of the mixture within the combustion chamber.

Gases evolved from the combustion of the products in the combustion chamber increase in pressure until such time as the small area surface on the control piston for the main valve produces a net force exceeding the closing bias from the compressed air. At this time the main valve is shifted to its open position, and the gases from the combustion chamber enter the cylinder to drive the piston and driver through a power stroke. These gases are vented at the end of the power stroke, and the main valve is again closed to condition the tool for a further cycle of operation sequenced by the control valve assembly in the manner set forth above. The cost of the fuel used to power the tool is substantially less than the cost of the powder cartridges previously used. In addition, by using the valved arrangement in combination with the combustion chamber, the power output derived from the tool can be increased because only high pressure gases are admitted to the cylinder. Further, by regulating the pressure of the compressed air supplied for biasing the main valve in its closed condition, the pressure at which combustion products enter the cylinder can be controlled with the resultant control in the driving power afforded during each stroke.

Many other objects and advantages of the present invention will become apparent from considering the following detailed description in conjunction with the drawings in which:

FIG. 1 is a cross sectional view of a combustion powered fastener driving tool embodying the present invention;

FIG. 2 is a fragmentary sectional view taken along line 2--2 in FIG. 1;

FIG. 3 is a sectional view taken along line 3--3 in FIG. 1;

FIG. 4 is an enlarged fragmentary sectional view illustrating a control assembly in a position for effecting purging of the tool;

FIG. 5 is an enlarged sectional view similar to FIG. 4 illustrating the control assembly in another or second setting for supplying a metered charge of combustible material to a combustion chamber in the tool;

FIG. 6 is a view similar to FIGS. 4 and 5 illustrating the control assembly in a third setting for supplying compressed air to the fuel charge in the combustion chamber and illustrating the tool at a moment immediately following the ignition of the fuel in the combustion chamber; and

FIG. 7 is an enlarged fragmentary sectional view illustrating a drive piston and driver assembly at the end of a power stroke.

Referring now more specifically to FIG. 1 of the drawings, therein is illustrated a high pressure stud or fastener driving tool which is indicated generally as 20 and which embodies the present invention. The tool 20 includes a housing indicated generally as 22 including a generally vertically extending forward head portion 22A to the upper end of which is connected a generally rearwardly extending handle portion indicated generally as 22B. The head portion 22A includes a combustion chamber 24, the lower end of which communicates with the upper end of a cylinder 26 in which is slidably mounted a piston 28, to the lower end of which is connected a driver element or blade 30. The driver blade 30 is adapted to pass through and be slidably movable within a drive track or opening 32 in a fastener receiving structure or nosepiece 34, the lower end of which is adapted to be placed against a workpiece into which a fastener or stud 36 is to be driven. A main valve or main valve assembly 38 controls communication between the combustion chamber 24 and the cylinder 26.

A control or control valve assembly indicated generally as 40 disposed within or on the handle portion 22B of the housing provides means for shifting and biasing the main valve assembly 38 using a pressurized fluid such as compressed air supplied from a compressor or other suitable source 42. The control assembly 40 also supplies in its various settings a metered charge of a combustible material such as propane gas derived from a source 44 to the combustion chamber 24, in combination with a quantity of compressed air from the source 42. When the tool 20 is in the state illustrated in FIG. 1, the combustible mixture is supplied within the combustion chamber 24, and the main valve assembly 38 is biased to its illustrated closed position by compressed air. Actuation of an ignition control means indicated generally as 46 connected to and including an ignition element such as a spark plug or glow plug 48 ignites the mixture within the combustion chamber 24. When the pressure of the gas generated by the combustion process overcomes the pneumatic bias applied to the main valve assembly 38, this valve is opened, and the high pressure combustion products enter the upper open end of the cylinder 26 to drive the piston 28 and the driver element 30 through a power stroke during which the fastener 36 is driven into a workpiece. After this power stroke, the control assembly 40 can be operated to annother setting in which the main valve assembly 38 is held open, and compressed air is moved through the combustion chamber 24 and the cylinder 26 to purge the tool 20 of combustion products. After the piston 28 and the driver 30 have been manually restored to a normal position and a fastener 36 inserted into the drive track 32, the control valve assembly 40 can be operated through its sequence of settings to permit another cycle of operation of the tool 20 under the control of the ignition control means 46. Adjustment of a regulator shown schematically as 50 permits the power of each driving stroke to be controlled.

Referring now more specifically to the construction of the housing 22, this housing includes a generally cylindrical block or member 52 with an inner opening defining the combustion chamber 24. The open lower end of the opening defining the chamber 24 is threaded and threadedly receives an internally threaded sleeve 54 to which the upper end of the cylinder 26 is threadedly connected. The upper end of the sleeve 54 includes a tapered surface 54A forming a seat for the main valve assembly 38. The lower end of the cylinder 26 is threadedly secured to the nosepiece structure 34. This structure includes a cup-shaped member 56 secured in position by a set screw 58 to stabilize the tool 20 when it is placed against a workpiece and also to prevent flying fragments resulting from driving the fastener 36 into the workpiece.

The main valve assembly 38 is disposed within the combustion chamber 24 and includes both a combined main and exhaust valve portion 38A and an actuating or controlling piston portion 38B. The valve assembly 38 is formed by a movable annular or cylindrical body 60 with a centrally disposed opening in which is mounted a center post 62 secured to the housing member 52 by a nut 64. To provide the main valve and exhaust portion 38A of the valve assembly 38, the body 60 is provided at its lower end with an outwardly extending portion 60A, and a flanged sleeve 66 is threadedly secured within the lower end of the opening in the member 60 with an annular resilient valve member 68 interposed between the flange on the sleeve 66 and the flared portion 60A of the valve body 60. The resilient member 68 seats on the valve seat 54A to provide the main valve for controlling the admission of driving gases to the open upper end of the cylinder 26.

To provide an exhaust valve assembly for the upper end of the cylinder 26, the lower end of the post 62 is provided with peripherally spaced recesses 62A, and the upper interior wall of the sleeve 66 is provided with enlarged diameter portion or opening 66A. In the closed position of the main valve assembly 38 shown in FIG. 1, the grooves or recesses 62A and 66A are in communication to connect the upper interior of the cylinder 26 with the space or opening within the valve body 60. A passageway 70 in the post 64 places this opening or cavity in communication with the atmosphere, thereby connecting the upper interior of the cylinder 26 to the atmosphere. When, for example, the main valve assembly 38 is moved to its open position shown in FIGS. 4 and 6, the grooves or recesses 62A and 66A are moved out of communication, and the exhaust system extending to the atmosphere including the passageway 70 is closed off from communication with either the interior of the cylinder 26 or the combustion chamber 24.

The piston portion 38B of the main valve assembly 38 provides means for controlling movement of the main valve assembly 38 between the closed position shown in FIGS. 1 and 5 and the open position shown in FIGS. 4 and 6. The piston portion 38B includes a piston portion 60B slidably mounted within a control cylinder 72 formed in the housing member 52 concentric with the post 62. The piston portion 60B includes a large area upper surface shown as 60C and a small annular surface 60D continuously communicating with or exposed to the combustion chamber 24. The area of the piston surface 60D is greater than the oppositely facing surface of the flanged portion 60A on the valve body 60 so that when the combustion chamber 24 is pressurized, there is a net upwardly directed component of force resulting from the piston surface 60D and exposed upwardly facing surface of the flanged portion 60A.

The net effective area on the piston surface 60D tending to move the member 60 upwardly is small compared to the area of the surface 60C. The control assembly 40 includes means for supplying compressed air from the source 42 over a passageway 74 in the member 52 to the control cylinder 72 to provide means for biasing the main valve assembly 38 toward and holding this assembly in its closed position. The difference in the effective areas on the piston surfaces 60C and 60D permits the attainment of extremely high pressure gases resulting from combustion in the chamber 24 before these gases are admitted to the cylinder 26 for driving the piston 28 by movement of the main valve assembly 38 to its open position. As an example, in one tool 20 constructed in accordance with the present invention the ratio between the area of the surface 60C and the effective area of the surface 60D is around 18 to 1. This means that is compressed air at a pressure of 100 psi is introduced into the cylinder 72, the main valve assembly 38 cannot be opened to admit driving media to the cylinder 26 until the combustion products in the chamber 24 reach a pressure of 1800 psi. By regulating the pressure of the compressed air supplied to the cylinder 72 using the regulating assembly 50, the pressure of the gases admitted to the cylinder 26 and thus the driving force attained on a given stroke cannot only be controlled but can be controlled in small value increments that previously could not be attained with high pressure fastener driving tools. It is believed that the useful range of ratios between the area of the large piston surface 60C and the effective area of the smaller piston surface 60D include from 5 to 1 to as high as 30 to 1.

The control assembly or control valve assembly 40 which sequences the various operations of the tool 20 is carried on the handle portion 22B of the housing 22. The handle portion 22B includes a lower handle member 80 and an upper handle member 82 which are secured together and to the housing member 52. The lower handle member 80 includes a centrally disposed cylindrical opening 81 in which is disposed a generally cylindrical body 84 whose inner end is threadedly connected to an opening in the housing member 52 communicating with the combustion chamber 24. A flanged or enlarged outer end portion 84A on the body 84 clamps the housing member 80 to the housing member 52. At its inner end the body 84 carries a check valve assembly indicated generally as 86.

This check valve assembly selectively supplies a combustible fuel and compressed air to the combustion chamber 24 in various settings of the control valve assembly 40. The check valve assembly 86 includes (FIG. 4) a valve cylinder 88 having different diameter portions in which is slidably mounted a valve piston 90 having an enlarged head portion 90A carrying a check valve O-ring 92. A retaining ring or washer 94 prevents displacement of the piston 90 from the cylinder 88 by engaging the left-hand end of the enlarged portion 90A. This enlarged portion 90A includes spaced slots or recessed areas 90B to prevent sealing engagement between the washer 94 and the left-hand surface of the head portion 90A of the piston. When the piston 90 in the position shown in FIG. 4, gas is supplied over a check valve inlet passageway 96 in the handle member 80 and passes through an opening 98 in the body 84, through the cylinder 88, and around the head portion 90A of the piston 90 to be supplied to the combustion chamber 24.

A central portion of the valve body 84 in cooperation with the handle member 80 and the opening 81 formed therein defines a combustible gas metering chamber. More specifically, a pair of spaced O-rings 100 and 102 carried on the body 84 seal off a central portion of the opening 81 to provide a gas metering chamber 104 communicating with a gas inlet-outlet passageway 106 formed in the handle member 80. A combustible gas is either supplied to the chamber 104 through the passageway 106 or discharged from the metering chamber 104 through the passageway 106 in dependence on the setting of the control valve assembly 40.

The right-hand or outer end portion of the valve body 84 provides a means for coupling the tool 20 and the control assembly 40 to the source of pressurized fluid or compressed air 42. More specifically, a compressed air inlet line 107 from the regulating assembly 50 is threadedly connected in the outer end of an opening 108 in the valve body 84 and the enlarged portion 84A thereof. The opening 108 is placed in communication with a compressed air inlet passageway 110 in the handle member 80 through a passageway 112 in the valve body 84. Although the line 107 is shown as being threadedly connected to the body 84, a quick release detachable coupling can be provided.

The handle member 82 provides means for coupling the control assembly 40 to the source of combustible fuel or gas 44 and also carries a manually adjustable control forming a part of the control valve assembly 40. More specifically, the handle member 82 includes a longitudinally extending bore or opening 114, to the right-hand end of which is threadedly connected one end of a line 116 extending to the fuel gas outlet of the regulator assembly 50. Thus, the right-hand portion of the opening 114 is normally supplied with the fuel gas. Slidably mounted within a slightly enlarged portion of the opening or cylinder 114 is a cylindrical valve body 118, to one end of which a rod or adjusting member 120 is connected so as to extend out of the opening 114 to the upper surface of the handle member 82 through a slot 122. The valve piston 118 carries three spaced O-rings 124, 126, and 128. As the valve body or piston 118 is shifted to its different positions, the O-rings 124, 126, and 128 cooperate with a plurality of passageways or ports, all of which are numbered or indicated as 130 to selectively interconnect different combinations of passageways in the handle member 80 and to supply combustible gas from the right-hand portion of the opening 114 to certain passageways in the handle member 80.

In the above description, reference to the various components of the control valve assembly 40 has been made with regard to FIG. 4 of the drawings in view of the enlarged nature of this drawing. In this drawing, certain of the passageways such as the passageways 96 and 110 are shown in schematic form to simplify an understanding of the ensuing description of the operation of the control valve assembly 40. FIGS. 1-3 of the drawings illustrate the mechanical realization or the mechanical form of these passageways. In general, the various control passageways are formed by providing the lower handle member 80 with a flat upper surface 80A (FIG. 2) and by forming certain of the passageways in this flat upper surface. The upper handle member 82 is also provided with a matching flat lower surface and a sealing gasket 131 is interposed between these flat surfaces of the handle members 80 and 82. A plurality of machine screws 132 then secure the two handle members 80 and 82 together with the sealing gasket 131 interposed therebetween. The positioning and mounting of the upper handle member 82 on the housing 22 is facilitated by a dowel or pin 134 extending between the left-hand end of the opening 114 and an aligned opening 136 in the housing member 52.

Referring now more specifically to FIG. 2 of the drawings, the air inlet passageway 110 throughout its greater extent is a groove or recess in the flat upper surface 80A of the handle member 80 and terminates at its right-hand end in a vertical passageway communicating with the opening 81 in the handle member. This vertical portion of the passageway 110 receives compressed air supplied through the opening 112 in the body 84. Similarly, the check valve inlet passageway 96 throughout its greater extent comprises a groove or recess in the flat upper surface 80A of the handle member 80. At its left-hand end a vertical portion of the passageway 96 places this passageway in communication with the inlet passageway 98 to the check valve assembly 86. The gas passageway 106 extending to the metering chamber 104 comprises a vertical passageway or bore. The flat upper surface 80A is also provided with an elongated slot, groove, or recess 138 which is used in conveying the fuel gas from the chamber 114 to the metering chamber 104 over the passageway 106.

The control assembly 40 also includes further means for controlling the supply of compressed air to the passageway 74 and thus to the control cylinder 72. More specifically, the flat upper surface 80A of the lower handle member 80 includes a recess, groove, or passageway 140, the right-hand end of which is selectively supplied with compressed air under the control of the position of the valve body 118. The left-hand end of the passageway 140 terminates in alignment with one end of a passageway 141 (FIG. 3) in the upper handle member 82. The passageway 141 extends to a port at the end of the handle member 82 aligned with the port terminating the passageway 74 in the housing member 52.

The control assembly 46 provides means for selectively igniting or initiating combustion of the mixture within the combustion chamber 24. The assembly 46 includes an electrical switch 142 (FIGS. 1 and 3) with a depending operator element 142A engaging an upper surface on a trigger 144. The trigger 144 is pivotally mounted between a pair of depending supports 146 by a pivot pin 148 (FIG. 3). The depending supports 146 form part of a supporting bracket to which the electrical switch 142 is secured, and the bracket in turn is secured to the housing member 52 by a plurality of machine screws 150. The switch 142 controls the connection of the glow plug 48 to a source of electrical current over suitable conductors (not shown). The glow plug 48 communicates with the interior of the combustion chamber 24 over an extension 24A of the combustion chamber (FIG. 1). Accordingly, when the trigger 144 is pivoted in a counterclockwise direction about the pivot pin 148 to elevate the operator 142A, the switch 142 is operated to energize the glow plug or spark plug 48, thereby causing ignition of the combustible fuel mixture within the combustion chamber 24.

To prepare the tool 20 for operation, an estimate is made of the power necessary to drive a fastener 36 into a workpiece. The regulator assembly 50 is then adjusted to provide the driving force necessary for the particular fastener driving operation under consideration. The regulator 50 can be of any of a number of types well known in the art and basically maintains the pressure of compressed air from the compressed air source 42 and the pressure of the combustible gas or fuel from the source 44 in the ratio to each other affording efficient combustion in the chamber 24. In one tool 20 constructed in accordance with the present invention using a propane gas source 44, the regulator 50 is set to provide, for example, compressed air to the line 107 from the source 42 at 100 psi and propane gas from the source 44 to the line 116 at five psi. If it is assumed, as in the representative example above, that there is a ratio of approximately eighteen to one between the effective area of the piston surfaces 60C and 60D, the pressure of combustion products within the chamber 24 must reach 1800 psi before the main valve assembly 38 will be opened to admit generated gas to the cylinder 26. The same ratio of pressures of compressed air to fuel is maintained by the regulator 50 in other settings. As an example, if greater driving power is desired, the pressure of the air supplied to the control cylinder 72 is raised to 200 psi and the pressure of the propane fuel supplied by the source 44 to the line 116 is raised to ten psi. In this setting, the pressure of the combustion products in the chamber 24 necessary to effect opening of the main valve assembly 38 is doubled from 1800 psi to 3600 psi.

At the end of each driving stroke of the tool 20 (FIG. 7), the piston 28 is at the end of its power stroke, in which position the lower surface of the piston 28 rests against a resilient or elastomeric bumper 152 disposed within the lower end of the cylinder 26. In this position, the interior of the cylinder 26 is vented to the atmosphere through a plurality of ports 154 designed for venting combustion products through the cylinder 26 at the conclusion of the power stroke of the piston 28 and the driver 30. The lower end of the cylinder 26 also includes a plurality of peripherally spaced openings 156 of greater area designed to assist in exhausting air from the cylinder 26 below the piston 28 during its power stroke. A generally cup-shaped deflector 158 is provided for deflecting any hot gases discharged from the cylinder 26 toward the workpiece and away from the operator.

The control assembly 40 is then operated to its first position in which the combustion chamber 24 and the interior of the cylinder 26 are purged of combustion products and the metering chamber 104 is supplied with a charge of combustible fuel from the source 44. More specifically, in this first position the operator 120 on the valve piston 118 is moved to the extreme right-hand position illustrated in FIG. 4 of the drawings. In this position, propane fuel from the line 116 contained within the opening 114 passes through the first passageway 130 into the passageway 138 and out of this passageway through the connected passageway 130 to the space bounded by the two O-rings 126 and 128 on the valve piston 118. The fuel then flows downwardly through the passageway 106 to be accumulated within the metering chamber 104. This fuel gas at, for example, a pressure of around five psi also flows through an opening 160 in the body 84 to be accumulated within the right-hand end of the cylinder 88 in the check valve assembly 86. This fuel biases the valve piston 90 to its extreme left-hand position determined by engagement of the enlarged portion 90A of the piston with the retaining ring 94. This insures that the check valve assembly 86 is opened.

In this setting of the control valve assembly 40, compressed air at around 100 psi flows from the line 107 through the opening 108, the passageways 110 and 112, the connected passageways 130, the check valve inlet passageway 96, the passageway 98, the cylinder 88, and past the enlarged portion 90A on the piston 90 to be supplied to the combustion chamber 24. In this setting of the control valve assembly 40, the passageway 74 is connected to the atmosphere over the passageway 140 inasmuch as this passageway terminates in a passageway 130 disposed to the left of the O-ring 124. Since the upper surface 60C of the piston portion 60B is connected to the atmosphere, compressed air supplied to the combustion chamber 24 moves the main valve assembly 38 upwardly to the position shown in FIG. 4.

This means that the compressed air supplied through the check valve assembly 86 to the combustion chamber 24 flows through the combustion chamber and the cylinder 26 to be discharged through the openings 154 which are opened because the piston 28 is in the lowermost position shown in FIG. 7. This flow of compressed air purges the chamber 24 and the interior of the cylinder 26 of combustion products resulting from the prior operation of the tool 20.

The operator then moves the control valve assembly 40 to its second position in which the main valve assembly 38 is moved to its closed position, and the fuel charge from the metering chamber 104 is transferred from this chamber to the combustion chamber 24. This position is shown in FIG. 5 of the drawings. In this position the operator element 120 is disposed substantially midway along the length of the slot 122. To assist in positioning the control valve assembly 40, the slot 122 can comprise a continuous slot along one edge and a series of three notches along an opposite edge to provide means for detenting the valve assembly 40 in its desired position against the bias supplied to the right-hand end of the valve piston 118 by the fuel gas disposed to the right of this piston within the opening 114.

In the position shown in FIG. 5 of the drawings, the O-ring 124 closes off communication between the atmosphere and the upper end of the control cylinder 72 over the passageways 74 and 140. In this position, the O-rings 124 and 126 provide communication through the adjacent passageways 130 for supplying pressurized fluid from the passageway 110 to the passageways 74 and 140. This pressurized fluid accumulates within the control cylinder 72 above the piston portion 60B and moves the member 60 to its lower position so that the main valve assembly 38 is now disposed in its closed position. In this position, the resilient valve element 68 seats on the valve seat 54A to close off communication between the interior of the cylinder 26 and the combustion chamber 24. Further, the upper interior of the cylinder 26 is vented over the exhaust system including the passageway 70, the opening in the interior of the element 60, and the recesses or grooves 62A and 66A.

When the control assembly or control valve assembly 40 is moved to this intermediate position, the charge of combustible material in the metering chamber 104 is also transferred to the combustion chamber 24 which is now sealed off from communication with the cylinder 26. More specifically, when the valve piston 118 is moved to the position shown in FIG. 5, the O-ring 128 closes off communication between the recess or groove 138 and the passage 106 extending to the metering chamber 104. The O-rings 126 and 128 place the passageway 106 in communication with the check valve inlet passageway 96 through the illustrated pair of passageways 130. Thus, the combustible material now flows over the passageways 106, 130, 96, and 98 to the cylinder 88. Since the interior of the combustion chamber 24 is substantially at atmospheric pressure, the pressurized combustible fuel gas in the cylinder 88 displaces the valve piston 90 to the position shown in FIG. 5 so that fuel gas enters and is confined within the combustion chamber 24.

With the control valve assembly 40 held in this intermediate position, the operator returns the piston 28 and the driver rod 30 to the normal position shown in FIG. 1, as by inserting an elongated rod through the drive track 32. The operator then disposes a fastener 36 in the lower end of the drive track 32 and places the nosepiece structure of the tool 20 adjacent the workpiece. The tool 20 is now in a condition in which the control valve assembly 40 can be operated to its third or final position preparing the tool for operation.

Thus, the operator now, by manipulation of the operator member 120, moves the control valve assembly 40 to the third position shown in FIG. 6 of the drawings. In this position, the metering chamber 104 is recharged with a combustible material, and compressed air is supplied through the check valve assembly 86 to the combustion chamber 24 to provide a combustible mixture, following which the check valve assembly 86 is closed.

In the third or firing position shown in FIG. 6, the O-rings 124 and 126 on the valve piston 118 maintain the supply of compressed air to the control cylinder 72 so that the main valve assembly 38 is held in its closed position. The O-ring 128 clears the adjacent passageway 130 so that the combustible gas from the cylinder or opening 114 is again supplied over the passageway 106 to fill the metering chamber 104. This gas also passes through the opening 160 to apply a low pressure bias to the small area right-hand end portion of the piston 90 in the check valve assembly 86. The O-rings 126 and 128 together with the two adjacent passageways 130 place the compressed air inlet passage 110 in communication with the check valve inlet passage 96. This compressed air flows through the check valve assembly 86 to pressurize the combustion chamber 24 and to provide a combustible mixture within the chamber 24. As set forth above, the chamber 24 was previously pressurized with a metered charge of propane gas at 5 psi. Thus, when in the assumed example compressed air at 100 psi is supplied through the check valve assembly 86, the chamber 24 is pressurized to 100 psi and contains approximately 5 parts of propane gas to 95 parts of air. When the combustion chamber 24 is thus pressurized, the check valve assembly 86 is closed by movement to the position shown in dot and dash outline in FIG. 6.

More specifically, both sides of the enlarged head portion 90A of the piston 90 in the check valve assembly 86 are subjected to pressures around 100 psi. However, the right-hand end of the piston 90 which communicates with the interior of the metering chamber 104 through the passageway 160 is pressurized at around 5 psi. Thus, a net force is provided shifting the piston 90 to the right to close off communication between the combustion chamber 24 and the components of the control valve assembly 40. The tool 20 is now in a condition to be fired inasmuch as the main valve assembly 38 is in its closed position, and the combustible mixture has been supplied to the combustion chamber 24.

The operator then pivots the trigger 144 in a counterclockwise direction about the pivot pin 148 to the position shown in dot and dash outline in FIG. 6. This elevates the switch operator 142A to operate the electric switch so that the glow plug 48 is energized. After a brief time lag sufficient for the glow plug 48 to reach ignition temperature, the gaseous mixture within the combustion chamber 24 is ignited or rapidly oxidized, and the gaseous by-products of this oxidation build up in pressure within the combustion chamber 24. In the assumed example in which there is an eighteen to one ratio between the effective areas 60C and 60D and with the compressed air at 100 psi supplied to the control cylinder 72, the gaseous products within the chamber 24, when they reach 1800 psi or slightly exceed this value, produce a force acting on the piston surface 60D which momentarily shifts the member 60 upwardly to the position shown in FIG. 6. At this time, the gaseous combustion products, at or in excess of 1800 psi, enter the upper end of the cylinder 26 and drive the piston 28 and driver blade 30 downwardly through a power stroke during which the fastener 36 is driven into the workpiece. When, by virtue of the expansion of the gaseous products from the combustion chamber 24 into the cylinder 26 and by virtue of venting the interior of the cylinder 26 when the piston reaches its lower position shown in FIG. 7, the differential opening the main valve assembly 38 disappears, and the bias continuously applied to the control cylinder 72 acts on the piston surface 60C to move the main valve assembly 38 to its closed position.

When the operator releases the trigger 144 to release the switch assembly 142, the energization of the glow plug 48 is terminated. The control valve assembly 40 can then be operated through the same sequence of three steps described above in conjunction with the further manual operations described above to prepare the tool 20 for its next operation.

Since the tool 20 uses only a small quantity of a low cost fuel, such as propane gas, and a small quantity of compressed air, the cost of each firing stroke of the tool 20 is substantially less than that incurred using powder charges or cartridge type tools. Further, by operation of the regulating assembly 50, the pressure of the compressed air supplied to the control cylinder 72 can be varied to control the pressure at which the gaseous products discharged from the combustion chamber 24 are admitted to the interior of the cylinder 26. By regulating this pressure, the power output derived from the tool 20 can easily be regulated. Further, since the regulating assembly 50 maintains the pressures of the compressed air from the source 42 and the fuel gas from the source 44 in step, a proper combustible mixture is always supplied to the chamber 24 by the control valve assembly 40 in various settings of the regulator assembly 50. Obviously, for different combustible materials, the proportion of air to the fuel may vary, and these differences are easily adjusted in the regulating assembly 50.

Although the present invention has been described with reference to a single illustrative embodiment thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art which will fall within the spirit and scope of the principles of the present invention.

Claims

What is claimed and desired to be secured by Letters Patent of the United States is:

1. A power actuated fastener driving tool comprising

a housing having a forward head portion and a rearwardly extending handle portion,

a cylinder and a fastener receiving structure included in said head portion,

fastener driving means including driver means movable relative to the fastener receiving structure and a driver operating piston slidable within the cylinder,

a combustion chamber in the housing,

fluid actuated valve means for controlling communication between the cylinder and the chamber to selectively admit gases from the chamber into the cylinder,

and manually operable control means on the handle portion of the housing for selectively supplying a combustible mixture to the chamber and controlling the operation of the valve means.

2. A power actuated fastener driving tool comprising

a housing having a cylinder and a fastener receiving structure,

fastener driving means including driver means movable relative to the fastener receiving structure and a driver operating piston slidable within the cylinder,

a combustion chamber in the housing,

fluid actuated valve means for controlling communication between the cylinder and chamber to selectively admit gases from the chamber into the cylinder, said valve means including a pair of oppositely facing piston surfaces with a first one of the piston surfaces communicating with the combustion chamber,

manually operable control means on the housing for selectively supplying a combustible mixture to the chamber,

and regulating means coupled to the control means and the second one of the piston surfaces for controlling the pressure of the gases admitted to the cylinder.

3. The power actuated fastener driving tool set forth in claim 2 including

a source of compressed air,

a source of combustible gas,

and means for coupling the source of compressed air through the regulating means to the second piston surface and for coupling the source of combustible gas through the regulating means and the control means to the combustion chamber.

4. The power actuated fastener driving tool set forth in claim 3 in which

the regulating means controls the pressure of the compressed air supplied to the piston surface and the pressure of the combustible gas supplied to the combustion chamber.

5. The power actuated fastener driving tool set forth in claim 3 in which

the control means includes means for selectively coupling the source of compressed air to the combustion chamber.

6. A single stroke tool for driving fasteners comprising

a housing defining a cylinder,

a piston slidably mounted within the cylinder,

a fastener receiving structure,

a fastener driver actuated by the piston and movable in the fastener receiving structure,

a combustion chamber communicating with the cylinder,

a main valve assembly normally in a closed position closing communication between the cylinder and the combustion chamber and movable to an open position placing the combustion chamber in communication with the cylinder, said main valve assembly including a piston portion movable independently of said piston and having a bias surface and an opposed surface in communication with the combustion chamber,

fluid biasing means coupled to the bias surface on the piston portion for holding the main valve assembly in its closed position,

means supplying a combustible mixture to the combustion chamber,

and means for igniting the combustible mixture in the combustion chamber to provide a quantity of high pressure combustion products in the combustion chamber, said products acting on the opposed surface of the piston portion to move the main valve assembly to its open position against the bias of the biasing means to permit the combustion products to drive the piston.

7. A power actuated tool comprising

a housing including a cylinder and a gas generating chamber communicating with each other,

a power output means including a piston movable within the cylinder,

valve means movable independently of said piston and having a closed position closing communication between the chamber and the cylinder and an open position placing the chamber and cylinder in communication,

piston means controlling movement of the valve means between its open and closed positions, one surface of the piston means communicating with the chamber,

biasing means for biasing the piston means to a position moving the valve means to its closed position,

and generating means for generating a short duration surge of high pressure gas in the gas generating chamber to move the piston means against the bias applied by the biasing means to move the valve means to its open position to admit the high pressure gas to the cylinder to drive the piston.

8. The power actuated tool set forth in claim 7 in which

the generating means includes means for supplying a combustible mixture to the chamber and means for igniting the mixture.

9. The power actuated tool set forth in claim 7 in which

the piston means includes a differential piston with a small area piston surface communicating with the chamber and with a large area piston surface,

and the biasing means applies a continuous fluid bias to the large area piston surface.

10. The power actuated tool set forth in claim 7 including

fluid control means for opening and closing the valve means independent of the generating means.

11. The power actuated tool set forth in claim 7 including

purging control means operable to open the valve means and to supply a volume of fluid through the chamber and cylinder to purge the gas therefrom.

12. A power actuated tool comprising

a housing having a cylinder and a combustion chamber,

a power output unit including a piston slidable in the cylinder,

valve means movable between an open position placing the chamber in communication with the cylinder and a closed position in which communication between the chamber and the cylinder is closed,

piston means for moving the valve means and including a first piston surface communicating with the combustion chamber for biasing the piston means to move the valve means to its open position,

a control valve assembly movable to at least two different settings, said control valve assembly including means operable in a first one of said settings for supplying a combustible material to the combustion chamber, said control valve assembly including means operable in a second one of the settings for biasing the piston means to move the valve means to its closed position,

and means for effecting combustion of the material in the combustion chamber with the control valve assembly in its second setting to generate pressurized gas in the combustion chamber to overcome the bias applied to the piston means by the control valve assembly so as to move the valve means to its open position and supply the gas in the chamber to the cylinder.

13. The power actuated tool set forth in claim 12 in which

the housing includes a control cylinder for the piston means,

the piston means includes a second piston surface for biasing the piston means to move the valve means to its closed position, said second surface being in the control cylinder,

and the control valve assembly includes means operative in the second setting of the control valve assembly for supplying pressurized fluid to the control cylinder to act on the second piston surface.

14. The power actuated tool set forth in claim 13 including

means for adjusting the pressure of the pressurized fluid supplied to the control cylinder to control the pressure of the generated gas supplied to the cylinder when the valve means is moved to its open position.

15. The power actuated tool set forth in claim 13 in which

the area of the second piston surface is substantially larger than the area of the first piston surface.

16. The power actuated tool set forth in claim 12 in which

the control valve assembly includes both a combustible gas metering chamber for supplying a given quantity of combustible gas and means for coupling the metering chamber to the combustion chamber in the first setting of the control valve assembly.

17. The power actuated tool set forth in claim 12 in which

the control valve assembly includes means operable to control the piston means to move the valve means to its open position.