Portable gas-powered tool with linear motor

This invention relates to a self-starting portable tool comprising a housing, <ul id="ul0001" list-style="none"><li>an elongated cylinder in said housing,</li><li>a piston having an upper face and a lower face, said piston being mounted in said cylinder to be driven between an upper position of rest and a lowermost position and forming a motor member,</li><li>a working member attached to said piston,</li><li>a combustion chamber formed within said housing, means for providing a fuel and air mixture in said combustion chamber,</li><li>means for igniting and exploding said mixture in said combustion chamber to drive said piston from said upper position to said lowermost position to operate said working member.</li></ul>

A portable gas-powered tool of the above- mentioned type is disclosed in DE-A 2 422 773. This reference discloses a high-pressure stud gun or fastener driving tool which comprises a housing provided with 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 the 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. This type of device requires a compressor which becomes a burden and an inconvenience in addition to the large initial expense required for investment in such equipment.

Accordingly, an object of the present invention is to provide a new and improved portable gas-powered tool with a linear motor which is capable of generating large forces without requiring an auxiliary power source.

As to achieve this object, the present invention is characterized in that said combustion chamber having the upper face of said piston defining a wall portion of said combustion chamber, a turbulence generator in said chamber, means for operating said generator independent of said piston, such that premixing and turbulence are imparted to the air and fuel in said chamber before initial ignition of the mixture in said chamber and before initial movement of said piston, wherein the turbulence generator consists of a fan disposed in said chamber and the means for operating said generator includes an electric motor self-contained within said housing and connected to said generator.

The tool can include means for returning the piston to its driving position after it has been driven and, further, means for admitting air under ambient pressure to the underside of the piston when it is in its driven position such that the pressure differential between the ambient pressure on the underside of the piston and the lower pressure on the other side of the piston is effective to return the piston to its driving position. Further, there are provided means for retaining the piston in its driving position after it has been returned thereto.

Independent claim 5 is related to a self-starting portable tool including a housing, a cylinder in said housing, a piston in said cylinder and forming a motor member, a working member attached to said piston, a combustion chamber formed within said housing, means for supplying fuel and air to said combustion chamber, means or igniting and exploding said mixture in said combustion chamber to drive said piston to operate said working member, means providing axially disposed inlet and exhaust ports to said combustion chamber for admitting air and for discharging the products of combustion, characterized in that said piston defines a wall portion of said combustion chamber, a turbulence generator in said chamber axially disposed between said inlet and outlet ports, means for operating said generator independent of said piston such that premixing and turbulence are imparted to the air and fuel in said chamber before initial ignition of the mixture in said chamber and before initial movement of said piston, and wherein the turbulence generator consists of a fan having its axis axially disposed in said chamber, which fan serves to scavenge said chamber after firing by directing air from said inlet port through said exhaust port whereby the initial and all subsequent strokes of the motor member are operated at substantially full energy output, and means for operating said fan includes an electric motor self-contained within said housing and connected to said fan.

In this embodiment the combustion chamber is opened and closed by a valve means that coacts with said inlet and exhaust ports and means for effecting movement of said valve means to close off said chamber prior to ignition and open said chamber after the working member has been driven to facilitate scavenging of said combustion chamber. The valve means includes a slidable sleeve that cooperates with the housing to effect opening and closing of the inlet and exhaust ports. Further, in this embodiment the tools includes trigger operated means for operating said valve means to control the opening and closing of said combustion chamber. Said combustion chamber operates the means for supplying fuel to said combustion chamber for igniting said fuel to drive said motor member.

Preferably, both of said embodiments of the invention have in common that the means for supplying fuel to said combustion chamber is a metering valve mechanism wherein a prescribed amount of fuel is supplied to said combustion chamber. Additionally, the means for igniting said tool may include a spark plug powered by a piezo- electric device. Furthermore both embodiments may include trigger-operated means for operating the means for supplying fuel to said combustion chamber and for igniting said fuel to drive said motor member.

Thus, in the portable tool of the invention, the available power acts on a linear motor which through the action of a mechanism connected to the motor can be used to drive fasteners, operate shearing devices and other attachments that require relatively large forces.

The two embodiments of tools as illustated in the attached drawings employ a linear motor in which the force output of the linear motor is generated independent of the movement of the motor itself. No starter or other device is employed.

Essentially, the piston of the three tools illustrated have a piston carrying a driving member which in one case can be connected to a suitable attachment for shearing, cutting, punching etc. and in the other embodiment is used to drive a fastener into a workpiece.

Referring to the operation of the tools, it is noted that actuation of the trigger results in a metered amount of fuel being introduced into the combustion chamber after the chamber has been sealed and subsequent actuation of a spark plug to ignite the turbulence mixture of gas and air in the combustion chamber to drive the linear motor, which in this case is a piston. In one instance, the piston is returned to its driving position by a spring, and in the other embodiments, the piston is returned to its driving position by differential air pressure. When the pistons have been returned to their driving positions, they are retained in place by the spring in the first embodiment and by friction by the other embodiment.

Numerous other advantages of the invention will become readily apparent from the following detailed description of the described embodiments, from the claims and from the accompanying drawings.

Brief Description of the Drawings

<ul id="ul0002" list-style="none"><li>Figure 1 is a partial cross-sectional side elevational view of a portable tool embodying the subject invention and illustrating the relative position of the principal components prior to the tool being operated;</li><li>Figure 2 is a partial cross-sectional side elevational view of a second embodiment of the present invention, a fastener driving tool, and illustrating the position of the principal components before the tool has been fired;</li><li>Figure 3 is a partial cross-sectional side elevational view of the fastener driving tool as shown in Figure 2 illustrating the position of the major components located at the lower end of the barrel section at the end of the linear motor driving stroke;</li><li>Figure 4 is an enlarged partial cross-sectional side elevational view of the components forming the ignition mechanism of the embodiment of Figure 2;</li><li>Figure 5 is a schematic diagram illustrating the ignition circuit of the embodiment of Figure 2.</li></ul>

Detailed Description

This invention is susceptible of being used in many different types of tools. There is shown in the drawings and will herein be described in detail three embodiments of the tools incorporating the invention, with the understanding that these embodiments are to be considered but exemplifications, and that it is not intended to limit the invention to the specific embodiments illustrated. The scope of the invention will be pointed out in the claims.

Exterior Features

Figure 1 illustrates a tool 20 including a housing 22 forming a handle portion of the tool and a cylinder 24 in which the linear motor, herein a piston 26, is disposed. Connected to the piston 26 is an operator or working member 27, which is connected to the desired attachment to be operated by the linear motor, or which can engage various devices for introduction into the workpiece, or for any other disposition. The linear motor or piston 26 is retained in the position shown by a spring 28. The housing 22 includes stop members 29 which extend radially inwardly to limit the upward travel of the piston 26.

Located within the housing 22 between a cap 32, the piston 26 and the adjacent sidewalls of the housing 22 is a combustion chamber 30. The cap is maintained in position relative to the housing by bolts 34.

Located within the combustion chamber 30 is a fan blade 36 which is connected to a shaft 38 operated by the electric motor 40. Actuation of the motor results in the fan creating a turbulence in the combustion chamber, which aids in increasing the efficiency of the tool by providing an improved air-fuel mixture, and improved ignition and flame propagation. The electric motor 40 is operated by a battery 42 located in the handle portion of the tool and interconnected by suitable connections, not shown. Also disposed in the combustion chamber is the spark plug 44, which is ignited by a suitable circuit described hereinafter.

It is to be noted that provision is made for a space 48 to be provided between the cap 32 and the housing 22 to permit the exhausting of gases from the combustion chamber 30 when the sleeve 50 surrounding the housing 22 is in the position shown in Figure 1 as is shown by the directional arrows. Cylinder 24 includes a slightly enlarged diameter upper end 24a, so that air can flow around the piston 26 and associated 0-ring when the piston is in the raised or driving position of Figure 1, and stop members 29 are circumferentially spaced from one another to define gaps 29a through which air may flow into the combustion chamber. A plurality of air inlet openings 24b are provided adjacent the lower end of cylinder 24 for introducing air into the cylinder.

Extending downwardly from the sleeve 50 is a depending portion 51 which is interconnected to the trigger mechanism 54 in the following manner. The trigger mechanism 54 includes a trigger 55 which is connected to a link 56, the lefthand end of which is connected to the depending portion 51 through a pin 58 extending through a slot 60 in the link 56. Thus, it can be seen that upward movement of the trigger 55 will result in upward movement of the sleeve 50 to close off the combustion chamber from atmospheric air.

The operation of the trigger 55 also operates the fuel control mechanism 52. The fuel control mechanism includes a rod 68 that extends downwardly into engagement with the trigger 55. This position is maintained as shown in Figure 1 by a compression spring 62 which extends between the fuel control valve housing 64 and a flange 66 integral with the rod 68.

The details of the fuel control mechanism include the housing 64 and the valve stem 70 which is provided with lands 72, 74. The space between the stem 70, housing 64, and lands 72, 74 defines a metering chamber 76. In the position shown in Figure 1, fuel is provided in the metering chamber 76 from the fuel container assembly 80 by the action of a fuel control valve 75. When the trigger 55 is moved upwardly the land 74 blocks off the entrance from the fuel container 80 and the land 72 unblocks the port 79 to interconnect the metering chamber 76 with the combustion chamber 30. Thus, the metered amount of fuel is introduced into the combustion chamber upon upward movement of the trigger 55. The design is such that the metering chamber 76 is opened to the combustion chamber 30 after the sleeve 50 has closed off the combustion chamber from the atmosphere.

A switch 77 is mounted on the housing of the tool, and is connected by suitable means, not shown, to the fan motor 40 so that the fan is operated when the switch 77 is actuated. It should be noted that the operator shall engage the fan switch 77 which turns the fan on to provide turbulence in the chamber 30 prior to operating the tool by movement of trigger 55. In addition, it is seen that the fuel container assembly 80 includes a pressurized chamber 82 which acts against the piston 84 to maintain the fuel in the container 80 in liquid form. The trigger further acts to force together crystals located in a piezoelectric device schematically illustrated at 46. Effectively upward movement of the link 56 about pivot pin 57 acts to force together two crystals disposed in device 46 to generate a voltate to power the spark plug 44. Further details of the device will be described in conjunction with Figures 4 and 5 herein, which specifically illustrate a piezoelectric device and the firing circuit.

Briefly, this tool operates as follows. First, the fan is started by engaging the switch 77. Upward movement of the trigger 55 closes off the combustion chamber 30 by moving the sleeve 50 to close off the exhaust port 48. As this occurs, further upward movement of the rod 68 introduces the fuel from the metering chamber 76 into the combustion chamber 30. The upward movement of the trigger 55 energizes the piezo-electric system 46, which provides a spark to the plug 44, which ignites the fuel to drive the linear motor piston 26 downward against the action of the spring 28. As soon as the piston 26 begins to move through its driving stroke, the 0-ring thereon seals against the sidewall of cylinder 24 and air below the piston is expelled through openings 24b. When the piston 26 reaches the driven position at the end of its driving stroke, it engages a resilient bumper 86 at the lower end of cylinder 24.

When the trigger is released, the sleeve 50 moves downwardly and the chamber 30 is opened to atmosphere through ports 48. The fan blades have a slight pitch to scavenge the rest of the gases and introduce the fresh air into the combustion chamber for the next firing, as is clear from the directional arrows. The piston 26 is returned to the position shown in Figure 1 by the spring 28, and a second metered quantity of fuel is provided to the chamber 76, so that the tool is in position to be fired a second time.

Reference is now made to Figures 2-5, which illustrate a portable fastener driving tool employing the novel linear motor.

Referring first to Figure 2, there is illustrated a fastener driving tool 100, the principal components of which are attached to or carried by a generally hollow housing 102. The housing 102 of the tool 100 has three major sections: a barrel section 108, a graspable, elongated handle section 110 extending horizontally outwardly from a position generally midway of the barrel section, and a base 106 extending under the barrel section and the handle section. Located within the barrel section 108 is a main cylinder 104 in which the linear motor is located. Included in the base 106 is a magazine assembly 112 holding a row of nails disposed transversely to the path of a fastener driver 132 that is connected to and operated by the linear motor, which in this case is a working piston assembly 130.

The lower end of the barrel section 108 carries a guide assembly 152 which guides the fastener driver toward the workpiece. The magazine 112 supplies fasteners serially under the fastener driver 132 into the guide assembly 152 to be driven into the workpiece. The base 106 also supports a holder 116 containing a plurality of dry cells which form the power source 118.

A fuel tank 114 is mounted between the barrel section 108 and the handle portion 110 of the housing 102. The fuel tank 114 is filled with a liquefied, combustible gas kept under pressure, such as, MAPP gas or propane, which vaporizes when it is discharged into the atmosphere. The fuel tank 114 is supported by a pivoted lower bracket 200 and a fixed, generally U-shaped upper bracket 202. The upper end of the fuel tank 114 carries a valve assembly 204 for metering fuel out of the tank. A flexible plastic cover 210 pivotably joined to a cover member 168 fits into the upper bracket 202 to retain the fuel tank in place. The cover 210 is opened when the fuel tank 114 must be replaced. The cover 210 provides a downward force which snugly holds the lower end of the fuel tank within the lower bracket 200. At this point, it should be noted that the upper bracket 202 has an inside dimension greater than the outside dimension of the fuel tank 114.

In particular, this dimension is selected so that when the upper end of the fuel tank is forced towards the upper end of the barrel section 108 of the housing 102, the valve assembly 204 will be actuated to dispense a metered quantity of fuel. The manner in which this is accomplished will be explained after the interior components of the tool have been described.

Barrel Section

At the interior of the lower end of the barrel section 108 of the housing 102, there is located the open-ended cylinder 104. The cylinder will hereinafter be referred to as the "main cylinder." The diameter of the main cylinder 104 relative to the diameter of the barrel section 108 of the housing 102 is such that an open generally annular zone or region 134 is formed. The barrel section of the housing 102 is formed with peripheral openings 103, which allow air to pass freely around the exterior of the main cylinder 104.

The driving piston 130 is mounted within the main cylinder and carries the upper end of the fastener driver 132. The upper end of the barrel section 108 of the housing 102 carries an electrically powered fan 122 and a main valve mechanism 124, which controls the flow of air between the combustion chamber 120 and atmosphere. The upper end of the housing located above the fan is closed by the cylinder head 126. The main valve mechanism 124 includes an upper cylinder 136, which together with the cylinder head 126, the main cylinder 104, and the piston 130 forms the combustion chamber 120. The electric fan includes a set of blades 123 which are joined to the output shaft of the electric motor 122.

The main cylinder 104 is closed at its lower end by a cup-shaped support casting 128 that is suitably supported in the barrel section. Located near the bottom of the cylinder 104 are a series of exhaust ports 156 that are closed off by exhaust valves 172 that are located to control the flow of gas out of the cylinder 104 when the piston linear motor 130 passes the ports 156. Connected to the cylinder 104 adjacent the ports 156 is an annular ring-shaped casting 173. At the bottom of the cylinder 104, a seal 158 is used to plug the center of the support casting 128. Also located in the support casting 128 are a plurality of ports 176 which interconnect the bottom of the cylinder 104 with the chamber 146 in which there is located a spring 148 for reasons to be described hereinafter.

The piston 130 moves between the opposite ends of the main cylinder 104. The upward and downward movement of the piston defines the driving and return strokes of the piston. As previously mentioned, valves 172 permit exhausting of the gas above the piston when the piston passes the ports 156 and the valves 174, which remain closed during the downward movement of the piston, provide for a compression of the air beneath the piston to provide a bumper preventing the piston from engaging the bottom of the cylinder. These valves 174 also function to open and introduce air into the space below the piston after the piston begins to be returned to its driving position. The piston 130 carries the fastener driver, which extends through the seal 158 and into the guide assembly 152. The guide assembly is configured to pass individual fasteners 154 that are disposed therein by the magazine 112, so that when the piston 130 is driven through its driving stroke a fastener is driven into a workpiece.

It is to be noted that the piston 130 includes a pair of O-rings that are sized so that the frictional force between the piston and the inside sidewalls of the main cylinder is sufficiently great so that in the absence of the differential pressure across the piston it will remain fixed in place relative to the interior sidewalls of the main cylinder when it is returned to its driving position. The upward movement of the piston 130 is limited by an overhang of the cylinder 104.

The cylinder 136 constituting the valve control for the combustion chamber is free to move between the lower position shown in solid lines in Figure 2 wherein the combustion chamber is open to atmosphere to permit air to flow in, as shown by the arrows 226 and an upper position shown in dotted lines wherein the combustion chamber is sealed off from the atmosphere by the 0-ring 162 provided in the cap 126 and the 0-ring 160 provided in the main cylinder 104. Air is thus free to enter through the upper opening 140 when the tool is in the position shown in Figure 2 and expended combustion gas is free to exit from the combustion chamber 120 through the opening 138. The downward movement of the cylinder 136 is limited by engagement of inwardly extending fingers 170 on cylinder 136 with cylinder 104.

It is essential to provide turbulence in the combustion chamber 120 to maximize the operating efficiency of the tool.

When the chamber 120 is opened to atmosphere, the position and configuration of the rotating fan blades 123 causes a differential pressure across the combustion chamber 120. This action creates movement of air in the chamber 120 and forces air in (arrow 226) through the upper openings 140 and out (arrow 224) through the lower openings 138. When the combustion chamber is sealed off from the atmosphere, and turbulence is created in the combustion chamber by rotation of fan 123, fuel is injected and the mixture is ignited. The flame propogation enhanced by the turbulence substantially increases the operating efficiency of the tool.

To insure that the tool cannot be fired until it is in engagement with the workpiece, the movement of the cylinder 136 is effected by a bottom trip mechanism which is operated when the tool is brought into contact with a workpiece into which a fastener is to be driven. In the embodiment illustrated in Figure 2, it includes a springloaded casting to which are connected lifting rods that are used to raise and lower the cylinder 136. Specifically, a Y-shaped casting 142 is located in the chamber 146 between the guide assembly 152 and the lower end of the support casting 128. Connected to the casting are three lifting rods 144A, B and C which interconnect the casting 142 to the cylinder 136. Extending downwardly from the casting 142 is a cylinder mount 147. The spring 148 in the chamber 146 acts to bias the casting 142 into the position shown in Figure 2. Located within the cylindrical mount 147 is the main lifting rod 150 which when moved upwardly moves the rods 144A, B, and C upwardly, which carries with it the cylinder 136 to close off the combustion chamber. The design is selected so that engagement of the main lift rod with the workpiece raises the cylinder 136 the prescribed amount to the broken line position shown in Figure 2 to seal the combustion chamber. Accordingly, when the tool is lifted off from the workpiece, the spring 148 biases the lifting rod 150 downwardly to move the cylinder 136 to the full line position shown in Figure 2 wherein the combustion chamber is open to atmosphere.

All the major components fitting within the barrel section 108 of the housing 102 have been described with the exception of those components that are joined to the cylinder head 126.

The cylinder head 126 carries the electric fan 122, a spark plug 164, and provides an internal passageway 166 through which fuel is injected into the combustion chamber 120.

The components located within the handle section 110 of the housing 102 will now be described.

Handle Section

The handle section 110 contains the controls used to operate the tool 100. In particular, the handle section 110 contains a "deadman's" switch 178, a trigger mechanism 180, a piezoelectric firing circuit 182, which activates the spark plug 164, a portion of a fuel ejecting mechanism 184, which introduces fuel into the combustion chamber 120 via the passageway 166 in the cylinder head 126, and a firing circuit interlock mechanism 188, which locks and unlocks the trigger mechanism 180.

The deadman's switch 178 is mounted at the top of the handle 110. It is suitably connected through appropriate mechanism to operate the electric motor 122 to drive the fan 123. Thus, it can be seen that when the user of the tool grips the handle in the forward position, the fan 122 is actuated to provide turbulence in the combustion chamber 120.

The trigger mechanism 180 mounted in the handle includes a lever 190 which is pivotally connected to a piezo-electric firing circuit 182 by a pin 192. The trigger button 194 is joined by a pivot pin 196 to the fuel ejecting mechanism 184.

The fuel ejecting mechanism 184, which functions to introduce a prescribed metered amount of fuel into the combustion chamber, includes an actuating link 212 which interconnects the trigger 194 to a camming mechanism 214. The operation of the trigger through the linkage 212 and camming mechanism 214 acts to move the fuel tank 114 to the left, which results in depression of the outlet nozzle 206 to introduce a metered amount of fuel into the passageway 166 from the metered valve assembly 204. It is noted that the tank 114 is retained in position by means of the cover 210 which is interengaged with the upper bracket 202. When the trigger is released, the spring 208 acts to return the fuel tank to the position in Figure 2.

The fuel injected into the combustion chamber 120 is ignited by a spark plug 164 powered from the piezo-electric firing circuit 182. Figures 4 and 5 illustrate the firing circuit 182. According to the piezoelectric effect, voltage is produced between opposite sides of certain types of crystals 182A, 1828 when they are struck or compressed. Here a camming mechanism actuated by the lever 190 and pivot pin 192 is used to force together the two crystals 182A, 182B. An adjusting screw 183 sets the preload to the assembly. A schematic diagram of the electrical circuit between the spark plug 164 and the piezo-electric firing circuit 182 is illustrated in Figure 5 and includes a capacitor C and a rectifier R. The capacitor C stores energy until the spark discharges, and the rectifier R permits spark to occur when the trigger is squeezed and not when the trigger is released. The piezo-electric firing circuit 182 is tripped when the lever 190 is raised upwardly by the trigger mechanism 180. Before the firing circuit can be refired or recycled, the lever 190 must be lowered to cock the cam used to force the two crystals 182A and 182B together.

There remains to describe the firing circuit interlock mechanism which precludes firing of the tool until all components are in their proper position. This includes links 216 which are connected to the trigger mechanism 180 by a tension spring 220 and a pivot pin 222. Connecting links 216 are located on opposite sides of the fuel tank 114. It can be appreciated that with the pin 218B located in the slotted opening 198 of the handle 110 that until the cylinder 136 is moved upwardly by the upward movement of the rods 144A, B, and C, the trigger cannot be actuated to form the spark to ignite the fuel in the combustion chamber. Upward movement of the rods 144A, B, and C moves the links 216 upwardly and withdraws the pin 218B out of the slot 198, thus permitting the trigger 194 to be moved upwardly to introduce the metered fuel into the combustion chamber and actuate the piezoelectric circuit. Stated another way, the trigger cannot be actuated to introduce fuel and create a spark until the workpiece is engaged to move the guide assembly upwardly, which moves the casting 142 upwardly to free the trigger 194.

Briefly, the tool disclosed in Figures 2-5 operates as follows.

Grasping of the tool 110 engages the deadman's switch 178 to start the fan motor 122 to rotate the blades 123 to provide turbulence in the combustion chamber 120. With the electric fan running, a differential pressure is produced across the combustion chamber, which acts to force fresh air in (arrow 226) through the upper openings 140 and out (arrow 224) through the lower opening 138. The rotating fan blades produce a swirling turbulent effect within the combustion chamber. Any combustion gases remaining in the combustion chamber due to the previous operation of the tool are thoroughly scavenged and discharged from the combustion chamber by operation of the electric fan 122.

When the tool is positioned on the workpiece, the main lifting rod is depressed, as shown in Figure 3, which overcomes the force of the biasing spring 148 to move lifting rods 144A, B, and C, and the cylinder 136 from its lower position shown in solid lines to its upper position shown in dotted lines to seal off the combustion chamber 120. This upward movement of the lifting rods also activates the firing circuit interlock mechanism 188. That is to say that the links 216 and associated pins 218B are pulled out of the slot 198, thus permitting the trigger 194 to be moved upwardly. Upward movement of the trigger 194 actuates the fuel injecting mechanism by moving the container to the left through the action of the linkage 212 and camming mechanism 214. This results in engaging the metering valve assembly 204 to introduce a metered amount of fuel into the passageway 166 and the combustion chamber 120. During upward movement of the trigger 194, the crystals 182A and 182B are forced together to actuate the piezo-electric firing circuit 182, which fires the spark plug 164 in the combustion chamber 120.

The rapid expansion of the exploding air and fuel mixture pressurizes the upper face 130A of the piston 130 and drives the fastener driver downwardly wherein it forces a fastener 154 into a workpiece. In addition, the movement of the piston 130 through its driving stroke compresses the air within the main cylinder 104 bounded by the lower face of 130B of the piston and the inside of support casting 128. As the pressure increases below the piston 130, the exhaust valve means 172 on the sidewalls of the main cylinder 104 pops open. As long as the exhaust valve means 172 is open, the pressure cannot build up on the lower face 130B of the piston 130. When the piston 130 passes below the ports 156, the air bounded by the lower face of the piston and the inside of the support casting is now isolated from the atmosphere, and the pressure on the lower face 130B of the piston rapidly increases. Effectively, a compression chamber has been formed in the lower end of the main cylinder which functions as a bumper to prevent the piston from striking the support casting 128.

Once the piston 130 has passed the ports 156 on the sidewalls of the main cylinder 104, the combustion gases are free to flow out of the main cylinder 104 through the exhaust valve means 172 to the atmosphere. The temperature of the gases in the combustion chamber rapidly drops from approximately 2000°F. to 70°F. in about 70 milliseconds due to the expansion of the gases as the piston moves downwardly and the cooling effect of the walls surrounding the expanding gases, and this sudden temperature drop produces a vacuum within the combustion chamber 120. Once the pressure within the combustion chamber is below atmosphere, the exhaust valve means 172 shuts off.

As soon as the pressure on the upper face 130A of the piston 130 is less than the pressure on the lower face 130B, the piston will be forced upwardly through its return stroke. Initially, this upward movement is caused by the expansion of the compressed air within the compression chamber (see Figure 3). Subsequent movement is caused by the pressure of the atmosphere, since the thermal vacuum formed within the combustion chamber 120 is on the order of a few psia. Additional air is supplied to the lower face 130B of the piston 130 through the return valves 174 which are opened by the atmospheric pressure. The piston 130 will continue upwardly until it engages the lip on the cylinder and will remain suspended at the upper end of the main cylinder by virtue of the frictional engagement between the sealing rings and the cylinder wall plus the force of the seal 158 on the fastener driver 132.

If the tool 100 is then lifted clear of the workpiece the main lifting rod 150 is forced outwardly by its main biasing spring 148. Since the electric fan 123 is still in operation, any remaining combustion gases are forced out of the lower openings 138, and fresh air is drawn in through the upper openings 140. This prepares the tool for firing another fastener into the workpiece. When the trigger button 194 is released the piezo- electric system 182 is reset or cocked for a subsequent firing period. When the main lifting rod 150 is driven downwardly by the biasing spring 148, the lock pin 218B within the firing circuit interlock mechanism 188 is forced back into the slotted opening 198 in the housing. This prevents subsequent operation of the trigger mechanism until the tool 100 is properly positioned on the workpiece and the combustion chamber is isolated from the atmosphere.

A portable gas-powered tool with this linear motor can be used for a variety of purposes, depending on the attachments connected to the motor. For example, as illustrated in the embodiment of Figures 2-5, it can be used to drive fasteners. Also, of course, attachments can be connected to the working member of the linear motor for shearing tree limbs, connecting hog rings, animal tags, piercing holes, marking metal plates, etc. In substance, it can be used anywhere where a large force is required. As stated, this tool is fully portable, can be light in weight, and thus can be used anywhere independent of the need for an external source of power, such as compressed air.

The motor is made possible in a relatively small portable tool by the creation of turbulence in the combustion chamber prior to and during combustion. This has not been done before in a portable tool and while it is acknowledged that internal combustion engines are notoriously old, these all require an external source of power in order to start the engine. The fan causes the air and fuel to be mixed to a generally homogeneous state under atmospheric conditions, and continued operation of the fan increases the burning speed of the fuel-air mixture in the combustion chamber prior to and during movement of the working member. In this tool, no external source of power is required and starting of the tool is totally independent of movement of the working member. This tool utilizes liquified gas, and thus is very economical to operate. Actually, it is about one half the cost of operating a pneumatic tool powered by a gasoline driven air compressor. As stated above, a relatively small portable tool adaptable for many uses can be designed employing the invention.

Thus, it will be appreciated from the foregoing description that the present invention provides an improved portable tool operated by a linear motor which has many advantages and improvements. While the invention has been described in conjunction with several embodiments, it is intended that many alternatives, modifications, and variations will be apparent to those skilled in the art.