GB2269888A

GB2269888A - Air guns

Info

Publication number: GB2269888A
Application number: GB9217449A
Authority: GB
Inventors: Philip John Crockett
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-08-17
Filing date: 1992-08-17
Publication date: 1994-02-23
Anticipated expiration: 2012-08-17
Also published as: GB2269888B; GB9217449D0

Abstract

An air gun has a barrel along which a pellet is driven by air compressed by the movement of a piston 12, under the action of a gas spring. The gas of the gas spring is compressed by a hydraulic actuator 50 supplied with hydraulic fluid under pressure by a hydraulic pump 52. The actuator includes a hydraulic cylinder 54 in which slides a piston 56 connected to a piston rod 30 arranged to drive a piston 32, so compressing gas in a chamber 40. The hydraulic pump is provided with a cocking lever 64, which is interlocked with the piston rod 30 to prevent operation of the gun other than when the gas spring has been fully charged. <IMAGE>

Description

AIR GUNS This invention relates to air guns, for example air rifles, air pistols, air shot guns and so on in which a projectile is expelled by air with energy stored in a compressed medium. In this specification the term air is intended to include any appropriate gas, e.g. carbon dioxide, unless the context dictates otherwise.

The background of the invention will be explained with reference to air rifles, although the invention is not limited to this application.

Air rifles generally have one of two basic operating mechanisms. In one, operation of a trigger releases a piston which is urged by a spring to compress air in a cylinder which in expels the projectile, in the form of a pellet, down a bore in the barrel. To prepare the gun for firing the spring must be compressed and that may be done by a lever mechanism operated e.g. by breaking the gun at the breach so as also to enable it to be loaded. In order to obtain greater power from the gun, the energy stored in the spring must be increased. That can be done by increasing the stroke and/or stiffness of the spring, but a practical limit is reached when the user no longer has the strength, or the inclination, to operate the lever mechanism.

In the other basic operating mechanism, operation of the trigger activates a valve to release a charge of pre-compressed air from a chamber to expel the pellet. The charge may be pumped up using a manual pump which is part of the gun, or may be released from a reservoir of pressurised air which is fitted to the gun and which had been precharged from a cylinder of compressed air or carbon dioxide.

In the pump up rifle, to begin with there is little pressure for the pump to overcome but this builds up as pumping continues. Choice of the mechanical advantage of the pump is thus a compromise, since if it is too great pumping will be frustratingly slow at the beginning whereas if it is too low the pressure which can eventually be reached will be unduly limited.

In the precharged rifle, the power which is obtainable is limited by the pressure of the source of compressed air or gas which is available and, further as the air or gas is released from the reservoir into the chamber during successive operations, the pressure in the reservoir is reduced so that the power of the gun varies.

Against this background, the invention broadly provides an air gun, wherein, in use, a projectile is expelled by energy stored in a compressed medium, the gun including a hydraulic actuator driven by a hydraulic pump to compress the medium at least partly.

The pump that is attached to the gun is preferably manually operated, although it is envisaged that the pump may be externally driven.

In one application the medium is a mechanical or gas firing spring.

In that application the gun may have a pneumatic firing piston slidable in a cylinder under action of the spring to displace air from the cylinder so as to expel a projectile down a bore. The arrangement allows the spring to be compressed by a plurality of strokes of the pump so that the effort required by the operator for each stroke is reduced compared with the single stroke operation of the known lever mechanisms.

Greater power may thus be obtained or less effort may be required to achieve the same power or a combination of both.

In one form the hydraulic actuator is operable to retract the piston in the cylinder against the action of the spring.

However, the mechanism may be more compactly made in accordance with a preferred feature which is that the spring operatively connects the actuator and the piston. In such an arrangement, the actuator, the spring and the pneumatic piston may be in line one behind the other.

The actuator is preferably in the form of a ram having a hydraulic piston connected to the firing spring.

Especially in the case of a gas spring, but also in the case of a mechanical spring, the firing spring may be conveniently contained in the firing piston.

When the spring is a gas spring it preferably comprises a spring piston coupled to the hydraulic piston and slidable in a bore in the firing piston.

In order to allow the gun to be cocked, valve means is preferably included for selectively permitting flow of hydraulic fluid from the ram to allow retraction of its piston; and retraction spring means is operative to retract the hydraulic piston, the firing spring and the pneumatic piston together.

In order to prevent damage to the mechanism being caused by firing the gun when the actuator is only partly extended, the gun preferably includes locking means to selectively lock the actuator in an extended condition; and interlock means for preventing the gun from being fired unless the actuator is so locked.

In order to indicate to the user that the actuator is locked and that the gun is thus firable, the locking means preferably comprises a lock member movable between a position locking the actuator and a position in which the actuator is free; and including a cocking lever for operating the pump and which in a home position urges the lock member towards its locking position. If the locking member does not move to its locking position, the locking lever cannot be returned to its home position.

In other applications, the gun includes: a chamber for compressed air or gas; and a valve selectively openable by a trigger mechanism to discharge the compressed air or gas to expel the projectile, the actuator being operable to reduce the volume of the chamber so as to compress air or gas therein.

In one application, a pneumatic pump is included for precharging the chamber with air. The hydraulic pump is used to reduce the volume of the chamber so as to compress the air in the chamber further, after it has been precharged by the pneumatic pump. This enables the chamber to be precharged with air by relatively few strokes of the pneumatic pump, which implies a relatively low mechanical advantage, and then reduced in volume by operation of the hydraulic pump at a relatively high mechanical advantage so as to obtain a suitably high pressure.

In another application, the chamber includes an inlet non return valve by which the chamber can be precharged with compressed air or gas. The arrangement allows the pressure of the air introduced through the inlet valve to be increased so as to provide additional power beyond that available from the source of compressed air or gas, and/or to compensate for reductions in the pressure of air in a reservoir mounted on the gun as the air therein is used.

In one convenient form, the actuator and the chamber are formed as a unit in one cylinder, a piston separating hydraulic fluid in one end of the cylinder from the air or gas in the chamber at the other, operation of the pump to pump hydraulic fluid into the cylinder thus moving the piston so as to reduce the volume of the chamber.

In another form, the chamber comprises a cylinder in which a piston is slidable, the actuator comprising a hydraulic ram operable on the piston to reduce the volume of the chamber.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a general side view, partly in section, of an air gun embodying the invention; Figure 2 is a detailed cross section of part of the mechanism of the gun of Figure 1; Figure 3 is a schematic detail of part of the mechanism of another gun embodying the invention; and Figure 4 is a detail of an alternative arrangement to that of Figure 3; Figure 5 is an end view of a piston of the apparatus of Figure 1; and Figure 6 is a cross-section of the piston of Figure 5.

Referring to Figure 1, the air gun illustrated is a rifle having a barrel 2, a stock 4, and a firing mechanism for firing the gun under control of a trigger 8.

Referring to Figure 2, the firing mechanism has a cylindrical casing 10 in which a pneumatic piston 12 is slidable and sealed by O-rins 14. In operating the gun, the piston is urged to the right, as shown in the drawing, by a spring to be described so compressing the air in the cylindrical casing 10 to project a pellet (not shown) down a rifled bore (not shown) in the barrel 2.

The piston comprises a cylindrical skirt 16 to the barrel end of which is welded or screwed a cast piston head 18. The skirt contains the spring which in the embodiment illustrated, is a gas spring. In other embodiments, the spring may be a mechanical coil spring (not illustrated). The O-rings 14 are located in a groove in the piston head 18. A plug 20 is screwed into the other end of the skirt 16, the space 22 thus defined inside the piston 12 being vented to atmosphere via holes 24 in the plug.

The plug 20 has a central aperture 26 in which a nylon bearing 28 allows a piston rod 30 to slide. At the barrel end of the piston rod is'a pneumatic piston 32 slidable in the cylindrical skirt 16 and sealed thereto by 9-rings 34. A passage 36 through the piston 32 and the piston rod 30 is sealed at the other end by a screwed plug 38 which enables the chamber 46 defined to the barrel side of the piston 32 to be charged with compressed gas or air.

A tang 42 extends from the plug 20 through a slot 44 in the cylindrical casing 10. With the piston 12 latched in the position shown by engagement of the tang 42 with the sear 46 of a trigger mechanism generally illustrated at 48, the piston 32 is urged towards the barrel, as will be explained, so reducing the volume of the chamber 40, and compressing the gas or air therein, until the piston 32 meets the piston head 18 which acts as a stop. Operation of the trigger 8 draws back the sear 46 so allowing the piston 12 to be urged forward towards to barrel by the action of the pneumatic spring, so that air in the cylindrical casing 10 is compressed by the piston 12 to propel the pellet down the bore in the barrel.

In order to compress the spring, the piston rod 30 is urged towards the barrel by a hydraulic actuator 50 supplied with hydraulic fluid under pressure by a hydraulic pump generally indicated at 52.

In the embodiment illustrated the actuator is a hydraulic ram comprising a cylinder 54 and a hydraulic piston 56 situated at the opposite end of the piston rod 30 from the pneumatic piston 32-. The piston 56 comprises a flange at the end of the piston rod 30 together with the plug 38. Between them a groove 58 is defined which receives an O-ring 60 to seal the piston in the cylinder.

Operation of the pump 52 forces hydraulic fluid into the cylinder 54 through an inlet port 52. The pump is operated by a cocking lever 64 which in its home position illustrated is retained by a latch generally indicated at 66. In contrast to conventional spring operated air rifles, the cocking lever 64 may be operated more than once to cock the gun. The overall mechanical advantage may thus be greater e.g. 5 or 10 times greater, so that less effort is required at each stroke by the operator to provide the same or greater total power.

Hydraulic fluid is drawn through an inlet port 68 from a reservoir 70 contained in the toroidal space between the cylindrical casing 10 and the cylinder 54.

To ensure no voids form in the reservoir the fluid is kept under constant slight pressure by an annular piston 72 sealed to both the casing 10 and the cylinder 54 by O-rings 74, which piston is urged away from the barrel by a spring 76.

It is important to ensure that before the gun is fired, the pneumatic piston 32 has fully compressed the pneumatic spring to the position shown in Figure 2.

Normally, the movement of the piston 12 is arrested by an end wall (not shown) of the cylindrical casing 10, in which end wall there is an aperture communicating with the barrel. If the gun were fired with the piston 32 in a position to the left of that shown, the plug 20 would strike the rear face of the piston 32 before the piston reached the end wall of the cylindrical casing. This could lead to damage, possibly destructive which would be very dangerous in a high power gun. This condition could result from the gun not being pumped up properly in the first instance or, having been properly pumped up, from leakage-back past the pump.

In order to avoid that possibility the rifle illustrated has a safety interlock generally indicated at 80. The piston rod 30 has a groove 82 between its ends. A locking member is slidable in an aperture 86 through the cylindrical casing 10 and a thrust member 88. The locking member 84 has a flange 90 towards its outer end. A spring 91 acting between the cylindrical casing and the flange urges the locking member out of engagement with the piston rod 30 and generally outwardly of the casing 10.

Fully extended from the casing 10 (not illustrated) the locking member is in the path of an interlock member 92 which moves rearwardly (to the left in the drawing) when the trigger 8 is pulled. Thus if the locking member 84 is not i-n the position illustrated, the trigger cannot be pulled to operate the rifle. When the cocking lever is pushed into its home position, as illustrated, it engages the locking member 84 and urges it into the position illustrated in the groove 82. If the groove 82 is not aligned with the locking member, the latter cannot enter the groove and so the cocking lever 64 cannot be latched in its home position, indicating to the operator that the rifle has not been fully pumped up.Once the cocking lever has been latched, the locking member 82 is retained thereby in the groove 82 so that hydraulic leakage cannot allow the piston 32 to creep back from the position illustrated.

Having fired the rifle, in order to re-cock it, a bypass valve (not illustrated) in the pump unit 52 is opened to allow hydraulic fluid to return from the cylinder 54 to the reservoir 70. Releasing the cocking lever 64 from its latch 66 frees the locking member 84 which is thus retracted from engagement in the slot 82 in the piston rod 30 by the spring 91. A spring 94 now acts against the piston 56 to retract it into the cylinder 54 returning hydraulic fluid into the reservoir 70 against the bias of the spring 76. When the gun has been fired, the pneumatic piston 12 has moved forward to a position in which the plug 20 is proximate the piston 32 which thus now acts to draw the piston 12 back as the piston 56 is retracted.Once the tang 42 has latched behind the sear 46, and the bypass valve has been closed, the pneumatic spring may be compressed again by operating the hydraulic pump 52.

Operation of the pump before the tang had latched would merely move the pneumatic piston 12 back towards the barrel in the cylindrical casing 10.

Ports, not illustrated, may be provided to allow an externally driven hydraulic pump (not illustrated) to be coupled in parallel to (or to replace) the manual pump 52.

In order to reduce the weight of the air rifle, aluminium is used where practicable. One situation in which aluminium is less suitable than steel is as a material in which a groove is machined to receive an Oring, i.e. as a material for the pistons 16, 32 and 56.

A form of construction suitable for the piston 32 and adaptable for construction of the pistons 16 and 56 is illustrated in Figures 5 and 6. Here the main body 20 of the piston is aluminium alloy. At one, or both ends, the body 120 is reduced in diameter to receive a ring 122 of chromium plated, chrome-steel, in which at least one groove 124 is machined to receive a respective piston ring in the form of an O-ring 126.

The ring 122 may be bonded by epoxyresin to the main body 120.

Referring to Figure 3, a different firing mechanism is illustrated schematically. A cylindrical chamber 100 communicates via a control valve 102 with the bore in the barrel 2. The chamber is pre-charged with air or gas via a non-return valve 104 either by a pneumatic pump (not shown) or from a reservoir (not shown). The reservoir is commonly refilled from a cylinder of compressed air or gas (not shown).

To fire the rifle, the valve 102 is opened by operation of the trigger mechanism (not shown) which allows the compressed air or gas from the chamber 100 to expand into the bore so projecting the pellet therefrom.

A pneumatic piston 106 is slidable in the cylinder 100 and sealed by an O-ring 108. The piston 108 is connected to the piston rod 110 of a hydraulic ram 112.

The ram 112 is actuated by a hydraulic pump (not shown) to drive the piston 108 to the right, as illustrated, so as to reduce the volume in the cylindrical chamber 100. This further compresses the air or gas therein.

In Figure 4, a hydraulic actuator is illustrated in the same cylinder as the chamber 100. Here Hydraulic fluid acts directly on one side of the piston 106 which is thus urged to reduce the volume of the chamber 100 increasing the pressure of the air or gas therein.

Claims

1. An air gun, wherein, in use, a projectile is expelled by energy stored in a compressed medium, the gun including a hydraulic actuator driven by a hydraulic pump to compress the medium at least partly.

2. An air gun as claimed in claim 1, wherein the pump is manually operated.

3. An air gun as claimed in claim 1 or 2, wherein the medium is a mechanical or gas firing spring.

4. An air gun as claimed in claim 3, having a pneumatic firing piston slidable in a cylinder under action of the spring to displace air from the cylinder so as to expel a projectile down a bore.

5. An air gun as claimed in claim 4, in which the hydraulic actuator is operable to retract the piston in the cylinder against the action of the spring.

6. An air gun as claimed in claim 4, in which the spring operatively connects the actuator and the piston.

7. An air gun as claimed in claim 6, wherein the actuator is in the form of a ram having a hydraulic piston connected to the firing spring.

8. An air gun as claimed in claim 7, wherein the firing spring is contained in thefiring piston.

9. An air gun as claimed in claim 8, wherein the spring is a gas spring comprising a spring piston coupled to the hydraulic piston and slidable in a bore in the firing piston.

10. An air gun as claimed in any of claims 7 to 9, and including valve means for selectively permitting flow of hydraulic fluid from the ram to allow retraction of its piston; and retraction spring means operative to retract the hydraulic piston, the firing spring and the pneumatic piston together.

11. An air gun as claimed in any preceding claim, including locking means to selectively lock the actuator in an extended condition; and interlock means for preventing the gun from being fired unless the actuator is so locked.

12. An air gun as claimed in claim 11, wherein the locking means comprises a lock member movable between a position locking the actuator and a position in which the actuator is free; and including a cocking lever for operating the pump and which in a home position urges the lock member towards its locking position.

13. An air gun as claimed in claim 1 or 2, including: a chamber for compressed air or gas; and a valve selectively openable by a trigger mechanism to discharge the compressed air or gas to expel the projectile, the actuator being operable to reduce the volume of the chamber so as to compress air or gas therein.

14. An air gun as claimed in claim 13, wherein the chamber includes an inlet non return valve by which the chamber can be precharged with compressed air or gas.

15. An air gun as claimed in claim 13 or 14, including a pneumatic pump for precharging the chamber with air.

16. An air gun as claimed in claim 13, 14 or 15, wherein the actuator and the chamber are formed as a unit in one cylinder, a piston separating hydraulic fluid in one end of the cylinder from the air or gas in the chamber at the other, operation of the pump to pump hydraulic fluid into the cylinder thus moving the piston so as to reduce the volume of the chamber.

17. An air gun as claimed in claim 13,14 or 15, wherein the chamber comprises a cylinder in which a piston is slidable, the actuator comprising a hydraulic ram operable on the piston to reduce the volume of the chamber.

18. A piston comprising a main body of aluminium or aluminium alloy, the main body having a section of reduced diameter at at least one end, and a steel ring engaging said section of reduced diameter and containing at least one groove to receive a piston ring.