Recoilless impact device

An apparatus for generating an impact against a target object comprises a driver reciprocally disposed in a housing. The driver includes a hollow tube having a closed end and a nozzle seating the other end. A piston is slidably positioned in the tube. Propellant is disposed between the piston and the closed end of the tube and fluid is disposed between the nozzle and the piston. A rupture disc is provided for sealing the nozzle which is adapted to rupture when the pressure in the tube exceeds a predetermined pressure. A striker is also mounted in the housing so that in a retracted position of the striker a head portion is proximate the driver and a portion of a shaft extends outwardly from the housing. The striker member is movable between the retracted position and an extended position. The propellant is ignited so that combustion gases build pressure in the tube between the piston and the closed end of the tube causing the pressure in the tube to exceed the predetermined pressure for rupturing the disc. This causes the piston to move toward the nozzle and fluid to be expelled through the nozzle for moving the driver against the head portion of the striker. The driver transfers energy to the striker for moving the striker to the extended position at high velocity for driving the end of the striker with great force against the target object. Recoil action is cushioned by the fluid exiting the nozzle.

BACKGROUND

This invention relates generally to hand-held impact devices, and more particularly to hand-held impact devices for gaining entry to locked or barricaded structures.

There is often a need for authorized personnel to rapidly gain access to locked, barricaded or otherwise secured buildings and to damaged structures, particularly in response to illegal activity or an emergency. Portable, hand-held forcible entry devices have been developed that enable law enforcement and emergency personnel to forcibly open a locked or fortified door, barricaded passage, damaged structure, or any other barrier that requires the use of force to gain access to a building or structure.

A typical forcible entry device comprises a piston-driven striker housed within a generally cylindrical case. The end of the striker extends from the front end of the case. A modified, conventional firearm is secured to the other end of the case for discharging the forcible entry device. The modified firearm fires a blank cartridge or other explosive charge which generates a combustion gas for driving the piston-driven striker outwardly of the housing to produce an extreme percussive force. In use, the striker is placed against a target object, such as a locked or barricaded door or damaged structure, and the firearm is fired. The striker extends from the front end of the case with great force and impacts the target object for breaking through the door or structure.

A problem with conventional forcible entry devices is the recoil generated when the device is fired due to the large force necessary to drive the striker. The recoil makes the device difficult for the user to hold and to control in use. Another problem with using forcible entry devices occurs when the target object offers little resistance to the striker. The force generated by the high velocity extension of the striker results in “forward” recoil wherein the device jerks forward in the user's hands. Forward recoil is also a problem when the devices are “dry fired”, that is, fired when the striker does not impact a target object.

For the foregoing reasons, there is a need for a new impact generating device for use in forcible entry of locked or damaged structure which is recoilless. The new device should be recoilless in the traditional sense and minimize forward recoil in the case of soft target objects or dry firing. Ideally, the new impact device should also be compact and lightweight, and thus portable enough to be rapidly positioned and deployed to gain access to a structure without the need for an external power source.

SUMMARY

Therefore, it is an object of the present invention to provide an impact generating device which is recoilless.

Another object of the present invention is to provide an impact generating device which minimizes forward recoil, even when impacting soft target objects or when dry fired.

A further object of the present invention is to provide a recoilless impact-generating device which is useful in forcible entry of a locked or damaged structure.

According to the present invention, an apparatus for generating an impact against a target object comprises a housing defining an interior chamber and having a closed first end and an open second end. A drive member is reciprocally disposed in the interior chamber adjacent the second end of the housing for movement relative to the housing from a first firing position to a second driven position. The drive member includes a hollow tube member having a first closed end and a second open end. A nozzle member having a plurality of openings is sealably mounted in the second end of the tube. A piston is disposed in the tube for movement relative to the tube and propellant is disposed between the piston and the closed end of the tube. Fluid is also in the tube between the nozzle member and the piston. Means are provided for sealing the openings in the nozzle member, wherein the nozzle opening sealing means is adapted to rupture when the pressure in the tube exceeds a predetermined pressure. A striker member having a head portion and a shaft portion is mounted within the interior chamber so that in a first retracted position of the striker member the head portion of the striker member is proximate the first end of the drive member and a portion of the shaft portion extends outwardly from the interior chamber through a passage formed in the closed end of the housing. The striker member is movable relative to the housing between the first position and a second extended position where the head portion is adjacent the first end of the housing. Means are provided for igniting the propellant so that combustion gases build pressure in the tube member between the piston and the closed end of the tube member causing the pressure in the tube member to exceed the predetermined pressure for rupturing the nozzle sealing means. This causes the piston to move toward the nozzle member and fluid to be expelled through the nozzle member for moving the drive member against the head portion of the striker member and to the driven position. The drive member transfers energy to the striker member for moving the striker member to the second position at high velocity for driving the end of the striker with great force against the target object. Recoil action in the apparatus is cushioned by the fluid exiting the tube member through the nozzle member as the piston moves toward the nozzle member.

DESCRIPTION

The impact generating device according to the present invention is similar to the forcible entry device shown and described in U.S. patent application Ser. No. 09/065,746, the contents of which are hereby incorporated by reference.

Certain terminology is used herein for convenience only and is not to be taken as a limitation on the invention. For example, words such as “upper,” “lower,” “left,” “right,” “horizontal,” “vertical,” “upward,” and “downward” merely describe the configuration shown in the Figures. Indeed, the components may be oriented in any direction and the terminology, therefore, should be understood as encompassing such variations unless specified otherwise.

Referring now to the drawings, wherein like reference numerals designate corresponding or similar elements throughout the several views, an embodiment of the impact device according to the present invention for use, for example, in forcible entry of locked or barricaded structures or doors is shown inFIGS. 1-4and designated generally at20. The impact device20includes a housing22, a front cap24and an elongated striker shaft26extending through the cap24outwardly of the housing. At the end of the striker shaft26is a tip28. The tip28may be any useful shape, depending upon the structure to be opened, removed or cut. For example, a chisel type tip28is shown in FIG.1. The tip28may be made removable, as in the present device20, to ease application of the device to different situations. An outer channel weldment30extends from the front end of the housing22to a key block assembly32at the rear of the housing. The channel weldment30is held in place by straps34which are secured around the housing20by threaded fasteners36. Unless otherwise specified, all of the parts of the impact device20are aluminum except the striker shaft26and tip28which are steel.

Referring now toFIGS. 5 and 8, the housing22defines a generally cylindrical interior chamber38. The front end of the housing22is sealed by the front cap24which is threaded into the housing22, and the rear end of the housing is open.

A striker assembly40and a driver assembly42are reciprocally disposed within the chamber38at the front and rear of the housing22, respectively. The striker assembly40comprises the striker shaft26and a striker head44. One end of the striker shaft26extends outwardly of the housing22from the interior chamber38through a central opening46formed in the front cap24. A brass bushing48fits in the cap opening46between the cap24and striker shaft26to permit the striker shaft to reciprocate freely relative to the front cap. Optionally, the cap46may be provided with an annular groove48for receiving an o-ring50which fits snugly around the striker shaft26to seal the space between the cap24and striker shaft. However, if the bushing48is machined to sufficiently close tolerance with the shaft26, the o-ring50is not necessary. The striker head44includes two generally cylindrical pieces, an outer striker head52and an inner striker head54. The outer striker head52has three spaced circumferential grooves: a forward groove56which holds a rubber wiper ring58, a middle groove60which holds a polymer guide ring62and a rear groove64which holds a copper contact ring66which is insulated from the outer striker head52. The inner striker head54is steel and includes four spaced guide pins68, only two of which are shown inFIGS. 5 and 8. The guide pins68are movably received in corresponding openings70in the rear of the outer striker head52so that the inner striker head54and outer striker head52fit reciprocally together. The outer striker head52also has an axial pass through opening72for receiving a reduced diameter portion of the inner end of the striker shaft26. The inner end of the striker shaft26has an internally threaded axial opening73for receiving a shaft screw74which passes through the axial opening72in the outer striker head52thus securing the outer striker head to the striker shaft. A small coil spring76is interposed between the inner striker head54and outer striker head52for biasing the heads apart.

A large coil spring78is disposed around the striker shaft26within the housing22. One end of the spring78is positioned against the outer striker head52and the other end of the spring is against the front cap24. The spring78biases the striker assembly40inwardly of the housing22. As best seen inFIG. 8, the inner diameter of the interior chamber38of the housing22is decreased intermediate the ends of the housing forming a seat80against which the inner striker head54is biased proximate to a front end of the driver assembly42(FIG.5). The size of the coil spring78is selected so that the space between the inner striker head54and outer striker head52is maintained by the striker head spring76.

Referring toFIG. 14, the removable tip28is shown in more detail. The tip28has an axial bore164for slidably receiving a pin166which is held in the tip28by a hollow, peripherally-threaded plug168which journals the end of the pin166. A key retainer170is secured to the end of the pin166by a cap172and screw174which is received in an axial threaded bore in the end of the pin166. A spring175is disposed around the pin166in the tip28. One end of the spring175is against the pin166head and the other end of the spring is against the plug168to bias the pin166and attached key retainer170inwardly of the tip28. The outer end of the striker shaft26is shown inFIG. 15to include a blind channel176defined along an axial bore178. A transverse slot180is formed at the inner end of the channel176. To attach the tip28to the end of the striker shaft26, the key retainer170is aligned with the channel176in the end of the shaft26and tip28pushed into the shaft along the depth of the channel. A counterclockwise turn (as seen inFIG. 15) of the tip28will cause the key retainer170to move along the slot180thus locking the tip28in place in the shaft26. Removal of the tip28is the reverse of attachment.

The driver assembly42is shown inFIGS. 9 and 10. The driver assembly42is similar to the recoilless propulsion unit shown and described in U.S. Pat. No. 5,099,764, the contents of which are hereby incorporated by reference, which expels a pressurized fluid from the unit through a nozzle using a closed-breech piston activated by a propellant charge.

The driver assembly42according to the present invention comprises a generally cylindrical hollow tube82, a piston assembly84and a nozzle assembly86. The tube82has a closed inner end88and an open rear end90and defines an interior chamber92. The closed end88of the tube82has an axial passage94of stepped diameter opening outwardly of the end of the tube. The open end90of the tube82is internally threaded and is slightly thicker, which strengthens this portion of the tube.

The piston assembly84includes a cup-shaped piston96slidably disposed in the interior chamber92adjacent the closed inner end88of the tube82. The piston96may be nylon for most fluids, but is preferably metal when gas permeability of the fluid is a consideration. The outer surface of the metal piston96is sealed against the walls of the interior chamber92by two spaced o-rings98with metal backing rings which fit in spaced circumferential grooves100in the piston. The o-rings98also serve as a guide for movement of the piston96in the tube82. Alternatively, the o-rings98and backing rings may be replaced by T-seals typically used in high-pressure dynamic sealing applications.

A frustoconical ring seal102fits between chamfered surfaces101,103at the front of the end of the tube82and the piston96. The piston96separates the interior chamber92of the tube82into front and rear variable volume chambers. The ring seal102prevents fluid, particular permeable gases, in the rear variable volume chamber from entering the front variable volume chamber. Preferably, the ring seal102comprises a polymer material, but could be a soft metal. Alternatively, the periphery of the front of the piston can be grooved and coated with a soft metal, such as copper or silver, for sealing the space between the piston96and tube82. In any case, the pressure of the fluid in the chamber92forces the piston96forward thereby compressing the ring seal102against the chamfered surface at the inner end of the tube82for sealingly separating the front and rear variable volume portions of the tube chamber92.

The piston96has a central recess104for retaining a propellant charge106. It is understood that the present invention is not limited to the type of propellant used. For example, a suitable propellant is Winchester231smokeless powder. Adhesive paper108seals the propellant106in the recess104which centralizes the propellant in a contained target area. Although not shown in the FIGs., the rear portion of the piston96may include a protrusion of slightly less diameter than the body of the piston96. As will be described below, when the impact device20is fired, the piston96is driven rearward with great force into the nozzle assembly86. The protrusion on the rear portion of the piston96strengthens the surface of the piston96that impacts the nozzle assembly86thereby minimizing the potential for deformation of the piston96edges.

A primer110is disposed in the axial passage94in the closed end of the tube82and held in place by a threaded plug112. Suitable primers110include M52A3B1 or PA520 military grade electrically-initiated primers available from Lake City (Ohio) Army Ammunition Plant. A small amount of electrical energy, approximately 1 mJ, will form an are within these primers which ignites a very small amount of propellant. The passage94serves to communicate the primer110with the propellant charge106in the piston96and directs gases from the primer into the front variable volume chamber.

Another embodiment of the driver assembly42according to the present invention is shown in FIG.16. In this embodiment, the primer110is disposed in a peripherally threaded cylindrical primer block182which is received in a larger diameter portion of the opening94in the inner end of the tube82. The primer110fits in an opening in the primer block and is held in place by a hollow, peripherally threaded retainer184. The retainer184defines an opening186in the primer block186that allows access to the inner end of the primer110. The large diameter primer block182provides a contact point for completing an electrical firing circuit as will be described below.

The nozzle assembly86includes a peripherally-threaded cylindrical nozzle114which is threaded into the open end of the tube82. An o-ring115seals the inner surface of the nozzle114against a shoulder119in the open end of the tube82. When CO2is the fluid, the o-ring is preferably polyurethane which is less susceptible to gas permeability. The inner surface of the nozzle114has a plurality of blind bores116(FIGS. 11A-11D) of stepped diameter. A small vent hole117leads from the end of each bore116outwardly of the nozzle114. A plurality of angled passages118branch from a point intermediate along the length of the bores116and open outwardly of the outer surface of the nozzle114forming elliptical openings in the bores and the outer surface of the nozzle. The hole pattern formed by the passage118openings in the outer surface of the nozzle114is selected so as to disperse the fluid in as many jets as possible without adversely affecting the flow characteristics of the fluid and to optimize the safety of the exit area of the nozzle114. The greater the exit area the more optimal the propulsion of the impact device20.FIG. 3shows another multiple hole pattern in the outer surface of the nozzle114. This pattern results from seven spaced bores116and four angled passages118from each bore116. The thickness of the nozzle114is determined by the structural integrity of the hole pattern and the flow characteristics of the fluid18through the passages118.

Fluid124contained within the second variable volume chamber is preferably a liquid and, more preferably, the fluid is liquid CO2. Liquid CO2is stored in the tube82as a high pressure liquid/gas mixture wherein liquid CO2fills from about 50% to about 95% of the volume of the chamber92. At CO2liquid levels below about 50% there is typically not enough power delivered for propelling the driver assembly42forward with sufficient force when the device20is fired. CO2liquid levels above 95% become too volatile since the CO2pressure will change due to temperature. Thus, the upper limit to the liquid level is determined based on an expected storage temperature range. A preferred CO2liquid level is about 75% at which the interior chamber92pressure will range from about 600 psi at 0° F. to about 3000 psi at 145° F. It is understood that other fluids may be used which have different preferred fill levels. For example, if water is the chosen fluid, the water preferably fills substantially 100% of the volume of the second variable volume chamber of the tube82.

A brass burst disc126is disposed in each bore114against the shoulder128formed where the bore changes diameter (FIG.11C). The burst disc126is formed from a brass shim stock with a protective coating. Each burst disc126is sealed in place with a hollow hex head retainer screw130for sealing the interior chamber92of the tube82. When liquid CO2is used as the fluid in the driver assembly42, the burst disc is designed to withstand3700 psi.

A simplified nozzle114design according to the present invention is shown inFIGS. 17 and 18. This nozzle114has seven straight passages188for fluid ejection. Each passage188is sealed by a burst disc126held in place by a peripherally threaded cylindrical retainer sleeve190. This nozzle114design is possible with the use of stainless steel non-fragmenting burst discs126available from BS&B Safety System of Tulsa, Okla.

As best seen inFIG. 18, the nozzle114also has a central fill hole120which opens into the interior chamber92of the tube82. A threaded plug122is provided for sealing the fill hole120. The plug122is a hollow modified set screw with an opening123that feeds into the interior92of the tube82when the plug122is slightly backed out of the hole120. An appropriate adapter (not shown) is provided on the plug122for coupling to a fluid feed line for loading the second variable volume portion of the interior chamber92of the tube82between the piston96and the nozzle114.

Means for retaining the driver assembly42in the housing22are provided. The driver assembly retention means comprises the key block assembly32mounted on the rear of the housing22. As best shown inFIG. 12, the key block assembly32includes a block132, a stop hammer136and a plunger138reciprocally disposed in the channel weldment30. The stop hammer136is a flat piece having an opening137therethrough which is reciprocally received in a slot in the block132. The key block assembly132is positioned over a peripheral slot140in the housing22(FIG. 5) which opens through to the interior chamber and allows the stop hammer136to extend into the housing22. The plunger138has a forward end141and a conically-shaped rear end142and is slidably disposed in the block132. The plunger138passes through the opening137in the stop hammer136. Movement of the plunger138in the key block assembly32relative to the stop hammer136moves the stop hammer136between a first position where a portion of the stop hammer extends into the housing22and a second position where the stop hammer is out of the housing. In the first position, the stop hammer136extends through the slot140in the housing and engages the rear of the tube82for securing the driver assembly42in the housing22. In the second position, the stop hammer136is in a non-blocking position with respect to the tube82so that the driver assembly42may be removed from the housing22. The stop hammer136is biased into the first, blocking position by one or more springs in the block132. A yoke144is shown connected to the front end of the plunger138for attachment to an appropriate release mechanism operable by the user.

In keeping with the present invention a firing mechanism is provided. It is understood that there are many ways to fire the primer110, including mechanical and electrical means. Preferably, the firing mechanism is electrical since electrical means are less prone to accidental actuation. The specifics of the electrical circuitry for firing the device20can be easily developed by those skilled in the art and will not be addressed. A preferred approach for carrying an electrical charge from a power source through the housing22and to the driver assembly42will be described. This approach includes first and second electrical contact plungers146,148schematically shown in FIG.5. The plungers146,148are spring-biased through respective openings in the housing22to a position adjacent the striker head44. The first plunger146is biased into an open area in the housing22between the outer striker head52and inner striker head54when the impact device20is in a non-firing condition. An electrical wire150(not shown) connected to the copper contact ring66passes through a transverse hole (not shown) in the outer strike head52and into the axial opening in the striker head44. The wire leads to an electrical plunger152(FIG. 9) disposed on the inner end of the driver assembly42and contacting the primer110for delivering electric current for firing the primer110. The ground connection is through the primer110skirt which is in close contact with the primer plug112. A plurality of electrical contact plungers200, two of which are shown inFIG. 8, nested in the rear end of the inner striker head54contact the primer plug112. The second plunger148is biased through the housing22and connects the inner striker head54to the electrical power source when the striker assembly40is in the firing position.

When preparing to fire the device20, the housing22is loaded with a driver assembly42through the open end of the housing. The inside diameter of the housing22is larger than the closed end of the tube82to facilitate loading. The closed end of the driver assembly42engages the stop hammer136which has a ramped surface139for allowing the advancing driver assembly42to force the stop hammer up into the block132. This movement is possible because the hole137in the stop hammer136is larger than the diameter of the plunger138. The driver assembly42is advanced until the rear of the tube82is clear of the stop hammer136which is biased into the housing to hold the driver assembly42in the housing22.

Referring now toFIG. 6, the tip28of the striker shaft26is then positioned against an object such as a locked door, damaged structure or other barrier to be opened and manual force applied to the device20toward the object. This moves the striker shaft26inwardly of the housing22pushing the outer striker head52against the inner striker head54against the force of the interposed spring76. When the outer striker head52is moved rearward, the first electrical contact plunger146engages the copper contact ring66on the outer striker head to complete the electrical circuit. Thus, the preferred firing mechanism requires the user to physically engage the target object with the striker shaft tip28and manually force the striker shaft26into the housing a predetermined distance to enable the firing mechanism. This is a safe arrangement which prevents accidental “dry” firing of the device20.

Another embodiment of the striker head44according to the present invention is shown in FIG.19. In this arrangement, the outer striker head52and inner striker head54fit slidably together. A contact assembly192is positioned in axial openings across the striker heads52,54for movement with the outer striker head52relative to the inner striker head54. The contact assembly192comprises a nylon contact holder194, a housing196, a probe contact198and a ground contact200. The contact holder194is fixed to a reduced inner end of the housing196which is formed from an electrically conductive material such as, for example, brass. The housing196has an axial bore which receives the electrically conductive probe contact198. The probe contact198is held in the housing196by a retaining ring202. A spring204is disposed in the housing196for biasing the probe contact198outwardly of the housing196. The housing196is slidably received in an insulator sleeve206positioned in the inner striker head54. The insulator sleeve206separates the ground contact200from the housing196. A wave spring208is disposed between the ground contact200and the inner striker head54for biasing the ground contact outwardly of the housing196and against the primer block182. A circular retainer disc210is fixed to the rear end of the inner striker head54to hold the contact assembly192elements in the inner striker head54.

In this embodiment of the striker assembly40, the periphery of the inner striker head54includes two peripheral grooves which hold electrically conductive contact rings212. The spring-loaded contact pins146,148are positioned in the housing22to engage the rings212in the both the non-firing condition and the firing position of the impact device20. Spring-biased contact pin assemblies214,216disposed in transverse passages in the inner striker head54electrically connect the contact bands212with the housing196and ground contact200, respectively. This provides the electrical path from the exterior of the housing22to the probe contact198and ground contact200. When the inner and outer striker heads52,54are brought together in the firing position of the impact device20, the probe contact198is extended from the rear end of the inner striker head54and engages the primer110. Since the ground contact200is against the primer block182the firing circuit is completed.

In either embodiment of the striker assembly40, a cup218may be secured to the front end of the outer striker head52. The cup218serves as a witness panel for a proximity sensor (not shown) positioned in the outer cylinder of the housing. The proximity sensor senses when the inner and outer heads52,54of the striker assembly40are compressed in the firing position of the impact device20. This is a redundant arming feature. When the impact device20is in firing position, the operator fires the device20by actuating the firing mechanism which delivers an electrical charge to the primer110. The primer cap110is discharged by the electrical charge. When the primer110fires, hot flame and gases generated by the primer pass into the first variable volume chamber through the passage94in the end of the tube82. The gases are directed by the passage94at a target area on the paper108retaining the propellant106. The primer gases penetrate the paper108and ignite the propellant106while simultaneously blowing the propellant around the first variable volume chamber.

Expansion of the propellant gases builds up pressure in the first variable volume chamber between the piston96and the front end of the tube82. The pressure increase generates a force on the piston96which is transferred to the fluid124. The propellant gases continue to expand causing fluid pressure to rise until the burst discs126are ruptured. In the embodiment of the nozzle assembly86employing fragmenting burst discs126, the vent holes117allow pieces of the burst discs126to be driven safely into the blind end of the nozzle bores116. The vent holes117are too small to let pieces of the discs126escape. Alternatively, spikes (not shown) extending from the blind end of the bores116for capturing the burst discs126could replace the vent holes117. The inner elliptical openings of the secondary nozzle passages118are small enough to prevent pieces of the burst disc from exiting the nozzle114.

The propellant gases continue to expand causing fluid124to be expelled through the nozzle114and into the atmosphere away from the user. Referring toFIG. 7, the momentum and the pressure generated by the fluid124expelled into the atmosphere force the driver assembly42forward against the striker head44which moves the striker assembly40towards the front end of the housing22with great force. The striker shaft tip28impacts against the locked door, damaged structure or other barrier so that the user, such as law enforcement or emergency personnel, may gain access to the building or structure. The recoilless feature of the device20is due to the Davis Gun Principle which holds that when a mass is expelled from a body there is an equal and opposite reaction generated propelling that body. In the present invention, the expelled fluid124generates a driving force. Since this reaction takes place within the housing22which is not rigidly attached to the propelling body, the result is no recoil transferred to the housing.

Ideally, the burning propellant generates a pressure in the first variable volume chamber acting on the piston which, after an initial increase, is relatively constant over time as the piston travels toward the nozzle. Eliminating an initial pressure spike when the propellant is ignited allows a less robust tube to be manufactured. This goal is realized in the present invention due to a number of factors related to interior ballistics principals for pyrotechnically driven devices. First, the ratio of propellant charge to the initial available volume of the first variable volume chamber contributes to the desired propellant ignition and initial burn cycle. Maintaining the proper ratio controls the explosive nature of the burning propellant and the rate of the initial pressure increase upon firing of the device. Too much propellant or too little volume can lead to too high of an initial pressure spike. The cup shape of the piston is also a factor in the chamber configuration to optimize the burning of the propellant. The initial location of the piston96sets the chamber volume which matches an optimum burning solution for the propellant. The position of the recess104and the retaining paper108fixes the propellant conditions and minimizes the initial area exposed to the primer flame and gases for slowing the initial propellant burning rate. Blowing the propellant around the chamber helps produce a consistent repeatable burn.

The pressure in the first variable volume chamber increases until the burst discs126rupture and fluid124is expelled from the nozzle. The burst discs126are designed to burst at a predetermined pressure in order to insure proper propellant burn pressure and temperature. As the piston96moves down the tube82, the first chamber volume ahead of the piston96increases proportionally to the amount of fluid124displaced. This increase in the first chamber volume directly affects the burning characteristics of the propellant charge106. The rate at which fluid124is expelled from the tube82is directly proportional to the number and total cross-sectional area of holes118in the nozzle114which determine the amount of resistant force, or back pressure, acting on the piston96as the piston moves down the tube and causes propellant to burn to a relatively steady rate. Thus, with a known initial volume of the first variable volume chamber and a specific nozzle design, a propellant charge106can be selected by those skilled in the art so as to generate a controlled propellant burn cycle and provide a desired pressure curve for the system.

In a preferred embodiment, the propellant charge is 4.1 g which occupies about 0.1496 cubic inches. The empty volume of the first variable volume chamber is about 1.988 cubic inches. Thus, the ratio of the propellant charge to the initial chamber volume is0.075. The driver assembly42is loaded with approximately 0.42 lbs. of liquid CO2. The burst discs retain at least an additional 1000-1200 psi of pressure before the discs break to properly initiate propellant burning. This configuration produces about 7000 psi of pressure within the propellant chamber and produces relatively constant pressure over time during firing. The impact force of the device20having these characteristics is designed to be 65,000 lbs. of peak force at 20 lb-sec impulse at ambient temperatures against a rigid surface. The liquid CO2turns into solid flakes, like snow, as it passes through the nozzle114. The driver assembly42is recessed into the housing22to create a cavity for the expanding CO2liquid-to-gas effect to increase impulse from the pressure generated by the phase change of the fluid.

The striker assembly40compresses the spring78between the striker head44and front cap24as the striker shaft26extends from the housing22. The spring78and air compressed between the front cap24and striker head44serve as a pneumatic damping mechanism for slowing the striker assembly40to a stop and minimizing forward recoil. A small vent hole156is provided in the housing22near the front end. Air is forced through the vent hole156only if pressure in the housing reaches a predetermined pressure, for example about 250 psi, which happens only if the striker is over-accelerated. This feature is particularly advantageous when the device20is dry-fired or a target object is easily penetrated when fired. The tube82is slightly tapered at the nozzle end90to allow propellant gases to vent between the piston assembly84and the tube wall to relieve the pressure in the driver assembly42as the piston96is nearing the nozzle114. The compression spring78returning the striker assembly40and driver assembly42into the housing to the pre-firing position shown in FIG.5.

After firing, the device is reloaded by advancing the plunger138which raises the stop hammer136away from the rear of the driver assembly42. The spent driver assembly42is slipped out of the housing22and replaced with a fresh driver assembly. The spent driver assembly is reusable.

An embodiment of the device20including a handle assembly157is shown in FIG.13. The handle assembly157is preferably formed from a fiber reinforced composite material which is both strong and light, and comprises two hand grips159extending transversely to the housing22. The handle assembly157accommodates a power source, such as a 9-volt battery. When the user holds the device20, the user's thumbs are over a forward safety button158and a rear firing switch160positioned on the outside of the device which is easily accessible to the user holding the device. In a preferred firing sequence, when the user pre-loads the device20by pressing the tip28against a rigid object, an LED under the safety button158lights signaling the user the device is pre-loaded. The user then presses the safety button158which powers up the device20. When the device20has enough energy to fire, an LED under the firing switch160lights and the user knows the device is ready to fire.

A pivoting release lever162on the rear of the handle assembly157is pressed downward to raise the stop hammer136and allow a spent driver assembly to be removed and replaced.

The previously described versions of the present invention have many advantages, including delivery of a large impact to a target object, such as a locked or damaged structure, while generating no recoil, even when impacting soft target objects or accidental dry firing. The device is a great improvement over existing forcible entry devices for gaining entry to locked or damages structures through doors or other barriers. The impact device of the present invention is also compact and lightweight. This reduces the amount of time required to gain access to the building or damaged structure. Further, the impact device is versatile enough to be utilized in the many different situations in addition to those noted above, including for forcibly cutting materials and the dispatching of animals to be processed for nutritional purposes.

Although the present invention has been shown and described in considerable detail with respect to only a few exemplary embodiments thereof, it should be understood by those skilled in the art that we do not intend to limit the invention to the embodiments since various modifications, omissions and additions may be made to the disclosed embodiments without materially departing from the novel teachings and advantages of the invention, particularly in light of the foregoing teachings. For example, the impact device of the present invention has numerous other applications including delivering destructive blows to objects or dispatching animals. The significant advantage of the device is the forceful impact delivered with no recoil. Accordingly, we intend to cover all such modifications, omissions, additions and equivalents as may be included within the spirit and scope of the invention as defined by the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a crew may be equivalent structures.