GB2249159A - Airguns - Google Patents

Abstract

An airgun has mounted, within its body 16, a pressure chamber 15 in which there is located a valve assembly for allowing compressed gas from a bottle 40 to enter a breech to fire a pellet from the airgun. The valve assembly includes an O-ring 8 which is deformed to provide an innermost sealing surface which approximates to the diameter of a gas discharge passage 2. Also disclosed is hammer assembly 30 (Figure 3) incorporating a moveable inertia weight, and a probe assembly 60 (Figure 6) incorporating an outer probe member to seal the breech end of the airgun barrel, and a slidable inner probe member which extends into the breech to position an airgun pellet therein. <IMAGE>

Description

AIR GUNS This invention relates to airguns, and is concerned particularly although not exclusively with pre-charged pneumatic airguns.

The concept of an airgun with a re-chargeable, highpressure gas reservoir as an energy store, of sufficient capacity to permit a number of shots to be fired from a single filling of the reservoir, is over 300 years old (see "Smith's Standard Encyclopedia of Gas, Air and Spring Guns of the World" by W.H.B. Smith, 1957 and "Airguns and Cther Pneumatic Arms" by Dr. Arne Hoff, 1972). It has relatively recently returned to popularity, perhaps partly because of the rising demand for very high standards of accuracy in the new sport of "Field Target" shooting and the general perception that accuracy is likely to be enhanced by the virtual absence of recoil when such guns are fired using conventional, lightweight pellets.A further factor may be that the continuing growth in the popularity of SCUBA diving has led to the widespread availability of facilities for re-charging reservoirs with air at high pressures at modest cost.

Nevertheless, many modern pre-charged pneumatic airguns fail to be entirely satisfactory in that their valve mechanisms require a heavy hammer blow to operate, have a tendency to require frequent servicing and/or do not ensure that all the gas released with each shot is used to the maximum efficiency, thus reducing the number of effective shots per reservoir filling.

Furthermore, the vast majority of modern, pre-charged airguns are single-shot devices, insofar as each shot involves the hand-loading of a projectile into the breech. Even those with magazines tend to have integral magazines which are generally agreed to be less convenient than detachable self -contained magazines, a number of which can readily be carried pre-loaded in a pocket and rapidly and easily be inter-changed with an empty magazine as required.

The inventors of the present invention have specialised in innovative airgun design for many years (see US Patent 4,709,686; US Patent 4,771,758; and US Patent 4,850,329). They have now developed an improved, pre-charged pneumatic airgun which substantially overcomes or mitigates the above problems.

It is relatively easy to design a "total-loss" or "dump valve" system, such that all the high-pressure gas stored immediately behind the valve is released when the valve is actuated e.g. by a trigger-released hammer. It is more difficult when it is desired to release only a small proportion of the stored gas each time, so that, as the pressure in the reservoir drops, the valve stays open very slightly longer each time, with the net effect that a substantially constant amount of energy is imparted to each succeeding projectile, thus achieving and maintaining the consistent performance which is so greatly sought after, until the pressure in the reservoir has dropped significantly. For convenience, this type of valve will be referred to herein as a "shuttle" valve.

A known way of attempting to achieve the objective of consistency is to have a small, secondary gas chamber located between the main reservoir and the breech. This secondary chamber is typically supplied with gas from the main reservoir via a regulator so that the pressure in the secondary chamber will not exceed the level set by the regulator. Thus the main reservoir may be charged with air or some other suitable gas at, say, 200 bar, while the regulator will be set at only 70 bar. It will be appreciated that substantially constant performance will be available until the pressure in the main reservoir drops below 70 bar. The disadvantages of this design approach are primarily complexity, durability and cost.

Many valve systems of both of the above types do manage to maintain for a period a reasonably acceptable standard of consistent, leak-proof performance, generally by using a relatively substantial resilient valve seating member, e.g. one made out of a plastics such as PTFE, and using a strong spring to help re-seat the valve after each shot. They do tend, however, to require fairly frequent servicing and adjustment to maintain their performance.

The pressure differential across such valves will also greatly help to shut them and to hold them shut.

Indeed, the surface area of engagement of the sealing members of the valve and, more importantly, the superficial area generated by the closed valve and on which the pressure differential will act, are both generally substantial by comparison with the crosssectional area of the gas passage being sealed by the valve. In consequence, the total force holding the valve shut tends to be very substantial and is able to deform the resilient valve member(s) to such a degree that problems of "creep", distortion and eventual leakage can arise. A further disadvantage of such arrangements is that a substantial force is needed to knock the valve open and the trigger-released hammer mechanisms needed to provide such a force have to be quite powerful.A spring which is powerful enough to provide such a hammer blow in a short movement would have to be so strong as to be relatively awkward or uncomfortable to cock manually. In consequence, the combination of a relatively heavy hammer and a long stroke are generally used to generate the necessary force. Unfortunately, a powerful hammer blow can slightly disturb the gun, while a long hammer stroke inevitably leads to a longer lock time, i.e. a greater period from the release of the trigger to the departure of the projectile from the muzzle.

Preferred embodiments of the present invention aim to achieve reliable, durable valve sealing performance while enabling the valve to be knocked open with a very light blow.

Analysis and experimentation suggest that the reason why conventional hammer-operated shuttle valve systems of the general type already described are relatively inefficient in their use of the high-pressure gas, in that they pass a relatively large amount of gas per shot, is because there is a tendency for the hammer, particularly the heavy and/or powerful and/or long-stroke hammers generally required, to bounce on the valve stem, thus allowing additional quantities of gas to escape at each bounce, which gas does not add efficiently to the energy imparted to the projectile because the said projectile will already be moving rapidly down the barrel as a result of the gas released at the first blow of the hammer.Commonly, the way of attempting to minimise this tendency to bounce is to employ a more powerful spring to help re-seat the valve - which means that the force of the hammer blow required to unseat the valve has to be increased.

Thus another aim of preferred embodiments of the present invention is to eliminate valve bounce and stop the inefficient secondary gas flows.

Preferred embodiments of the invention may overcome these difficulties, and enable a very light hammer blow to open the shuttle valve and prevent wasteful hammer or valve rebound.

More generally, according to a first aspect of the present invention, there is provided a valve assembly for use in an airgun, the assembly comprising: a valve body defining therein a gas passage having a valve seat at a mouth thereof; a valve member having a head to engage with said valve seat; and an elastomeric sealing member which, in use, provides an annular sealing surface between said head and said valve seat, which surface has a diameter approximating to that of said passageway.

Preferably, said valve member is slideably mounted in said passage.

Preferably, said sealing member comprises an 0-ring which is deformed to provide said sealing surface at an innermost diameter of said deformed 0-ring.

Said sealing member may be provided on said valve body or on said valve member.

In a second aspect, the invention provides an airgun hammer assembly having an inertia weight moveable within the hammer and means for adjusting the stroke of the hammer.

In a third aspect, the invention provides a probe for an airgun breech mechanism, the probe comprising an outer member having one end adpated to seal a mating end of the airgun barrel, and an inner member slideably mounted within the outer member and adapted to project within the airgun barrel to position a pellet therein, with clearance between the inner member and the barrel.

The invention extends to an airgun provided with a valve assembly, and/or a hammer assembly and/or a probe according to any of the foregoing aspects.

The invention, in another aspect, provides an airgun having a compressed gas supply and means for releasing charges thereof into a barrel of the airgun in order to fire the pellet from the gun. Such an airgun may further comprise any one or more of the features disclosed in the accompanying specification, claims, abstract and/or drawings, in any combination.

For a better understanding of the invention, and to show how the same may be-carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 shows, in sectional view, part of a pressure chamber and valve assembly for use in an airgun; Figure 2 is an exploded view of the valve assembly of Figure 1; Figure 3 is a detailed sectional view of a hammer assembly; Figure 4 is a part-sectional view of a breech assembly of an airgun, incorporating the parts of Figures 1 to 3; Figure 5 is a view similar to Figure 4, but showing the air gun in a condition just after firing of a pellet; and Figure 6 is a detailed view of a novel probe assembly of the airgun of Figures 4 and 5.

Referring firstly to Figures 1 and 2, a valve body 1 is formed with a central bore 2, in which there is slideably mounted the stem 3 of a valve member 4, having a head 5. The valve body 1 is provided with three 0-rings - an outer 0-ring 6, an intermediate 0-ring 7 and an inner 0-ring 8. A cap 9 screw- threadedly engages a reduced diameter portion 10 of the valve body 1. A transfer port 11 leads to a breech of the airgun, and is provided at a portion of the valve body 1 adjacent which a reduced diameter portion 12 of the valve stem 3 is disposed.

The valve assembly is disposed at the right hand end (as seen) of the pressure chamber 15 which is formed in the airgun body 16, as shown in Figure 4. At the left hand side of the pressure chamber 15 (as seen) there is disposed a locating member 16 for a spring 17, which is constrained between the locating member 16 and the head 5 of the valve member 4. The spring 17 urges the valve member 4 into a closed position within the valve body 1.

In use, the valve body 1 is located within a reduced diameter portion 18 of the air gun body 16, where the outer 0-ring 6 provides sealing between the valve body 1 and the reduced diameter portion 18.

The inner 0-ring 8 is forcibly distorted within a recess 19 defined between the cap 9 and the reduced diameter portion 10 of the valve body 1, as shown best in Figure 1. The distortion of the 0-ring 8 causes a small portion thereof to protrude from a small annular gap between the reduced diameter portion 10 and the cap 9, and it is this protruding portion of the inner 0-ring 8 which bears against the head 5 of the valve member 4. The intermediate 0-ring 7 serves to seal between the high pressure chamber 15 and the right hand side (as seen) of the inner 0-ring 8.

The pressure chamber 15 is supplied with gas (e.g.

air) under pressure from a bottle 40.

Figures 1 and 2 show how a conventional 0-ring is captured around the inner edge of the valve seat such that a small-diameter, circumferential sealing area is presented to the male surface of the valve, thus providing a resilient, elastic seal which is both extremely effective as a durable seal and is capable of being unseated with a comparatively light hammer blow. It will be noted that the diameter of the seal contact path and thus the superficial surface area within the seal and on which the pressure differential acts, is virtually the same as the diameter and cross-sectional area of the gas passage sealed by the valve. Thus the seating force generated by the pressure differential is minimum.

Although the preferred embodiment is for the 0-ring to be mounted around the periphery of the valve seat, it will be clear that similar benefits could be obtained by trapping the same size 0-ring on the valve head.

Because the force required to overcome the sealing force generated by the pressure differential is at a minimum, the hammer force can be very low and can readily be achieved with a light hammer and hammer spring and a short hammer stroke.

In Figure 1, the inner 0-ring 8 is of standard circular cross-section, and is compressed by the action of the cap screw-threadedly engaging with the reduced diameter portion 10, into the shape as illustrated, to provide the projecting sealing surface that is extremely close to the diameter of the passage 2 within the valve body 1. For example, the maximum diameter of the said sealing surface of the 0-ring may be less than 3mm greater than that of the passageway 2 - and more preferably less than 2mm - and even more preferably less than lmm. It may even be equal to or somewhat less than the diameter of the passageway 2.

The reduced diameter portions 13 on the valve stem 3 serve as labyrinth seals, in a known manner.

To eliminate hammer and valve bounce, a spring-loaded inertia weight has been incorporated in the hammer mechanism, the hammer itself has been given an adjustable hammer stroke and the hammer spring has been made adjustable, as shown in Figs. 3 and 4.

In the hammer assembly 30 shown in Figure 3, a hammer 31 engages one end of a hammer spring 32, the other end of which engages a screw-threadedly adjustable locating cap 33. Within the hammer 31 there is defined a chamber 34, within which an inertia weight 35 is slideably mounted, and is urged to the right (as seen) by a spring 36, constrained between one end of the chamber 34 and a facing end of the inertia weight 35. An adjuster screw 37 screw threadedly engages the hammer 31, and is formed with a head 38.

The whole hammer assembly 30 is located within the air gun body 16, as seen best in Figures 4 and 5.

In use, screw-threaded adjustment of the locating member 33 adjusts the spring power of the hammer spring 32. Screw-threaded adjustment of the adjuster screw 37 adjusts the stroke of the hammer. As may be seen in Figures 4 and 5, the head 38 of the adjuster screw 37 is adapted to impact with the right hand end (as seen) of the valve member 4.

In use, when the airgun is fired, the hammer is released and travels rapidly to the left (as seen). When the head 38 of the adjuster screw 37 impacts with the valve member 4, the inertia weight continues to travel and is subsequently returned under the force of the inertia weight spring 36. As will be understood by those skilled in the art, the masses, dimensions and spring strengths are so selected as to damp the bounce of the hammer 31 and the valve member 4, upon firing.

The inventors have previously invented a means of using an inertia weight to assist in reducing the tendency for a high-speed piston to bounce when it reaches the end of its stroke (see US Patent 4,850,329). This earlier invention had an important secondary function of increasing efficiency by allowing a higher proportion of the air trapped on the high-pressure side of the transfer port to travel to and through it; furthermore, there was no suggestion of incorporating a stroke-adjustment facility. The function of the present use of an inertia weight is entirely different in that it is intended to prevent high-pressure gas from escaping in a wasteful manner and the adjustable hammer stroke and spring are important features in that they permit the power of the airgun to be set with some precision and for the shortest possible stroke to be used commensurate with the desired power.

The combined effect of these improvements has been to achieve an extremely fast lock time, a very light, fulldamped hammer strike that causes no disturbance of the gun and extremely efficient use of high-pressure gas, such that the number of effective shots available from a single charged reservoir are upwards of twice as many as are available from other pre-charged pneumatic airguns with reservoirs of comparable capacity. Furthermore, the light operating forces and overall simplicity result in low manufacturing cost, simple and quick adjustment, and very high standards of durability.

The embodiment of the invention illustrated in Figures 4 and 5 may overcome the limitations of singleshot designs and integral magazines by incorporating a detachable pellet magazine - for example, as shown in European Patent Application No. 89 304607.8 (Publication No. 0 341 090) and which the present inventors are already using with great success in one of their spring-operated air rifles. However, one-piece loading probes, sometimes incorporating a transfer port, hitherto used in conjunction with such a pellet magazine, have not always proved able to provide the extremely precise and consistent seating of the pellet in the breech in the subject pre-charged pneumatic rifle, while allowing a relatively unrestricted flow path for the gas to reach the rear of the pellet, that is required for the very highest standards of accuracy.

An inventive solution to this problem has been to create a 2-part, spring-loaded probe, operated by a conventional manual bolt action. The construction of such a 2-part probe which may be used in the embodiment shown in Figures 4 and 5, is illustrated in Figure 6. It comprises an outer probe member 61, within which there is slideably mounted an inner probe member 62 of reduced diameter, which is urged to the left (as seen) by a spring 63. In this 2-part loading probe, the outer member of the probe is very slightly larger in diameter than the pellets which the gun is designed to use.In consequence, as the tip of the probe enters the magazine, the spring-loaded chamber in the magazine is forced to open very slightly, thus releasing the pellet and allowing it to be easily pushed into the breech, virtually eliminating any risk of the pellet travelling other than absolutely concentric with the bore or being damaged in any way during its travel. As the tip of the outer member of the loading probe engages the entrance to the breech, it creates an effective seal at the mouth of the breech by reason of being very slightly larger in diameter than the pellet.

The effectiveness of the seal can be improved by incorporating matching chamfers on the tip of the outer probe member and the entrance to the breech. The longitudinal stroke of the bolt action is not yet complete, however, and as it continues, the inner shaft of the loading probe also continues forward, thus projecting beyond the tip of the now-static outer member. This inner shaft, which is very much smaller in diameter than the diameter of the pellet, continues to insert the pellet further into the breech, until the pellet has passed over the transfer port. At this point the longitudinal stroke of the bolt action comes to an end and the bolt assembly is locked into its longitudinal position by a short, rotary lateral movement of the bolt in a conventional manner.When the gun is fired and the high-pressure gas flows through the transfer port, there is ample room for the gas to pass around the narrow, inner shaft of the loading probe and act on the rear of the pellet.

Such operation of the airgun will be apparent to the skilled loader, with reference to the above description and the accompanying drawings.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is also directed to the Patent Specifications and Applications mentioned herein.

Claims (14)

1. A valve assembly for use in an airgun, the assembly comprising: a valve body defining therein a gas passage having a valve seat at a mouth thereof; a valve member having a head to engage with said valve seat; and an elastomeric sealing member which, in use, provides an annular sealing surface between said head and said valve seat, which surface has a diameter approximating to that of said passageway.

2. A valve assembly according to claim 1, wherein said valve member is slideably mounted in said passage.

3. A valve assembly according to claim 1 or 2, wherein said sealing member comprises an 0-ring which is deformed to provide said sealing surface at an innermost diameter of said deformed 0-ring.

4. A valve assembly according to claim 1, 2 or 3, wherein said sealing member is provided on said valve body.

5. A valve assembly according to claim 1, 2 or 3, wherein said sealing member is provided on said valve member.

6. An airgun hammer assembly having an inertia weight moveable within the hammer and means for adjusting the stroke of the hammer.

7. A probe for an airgun breech mechanism, the probe comprising an outer member having one end adpated to seal a mating end of the airgun barrel, and an inner member slideably mounted within the outer member and adapted to project within the airgun barrel to position a pellet therein, with clearance between the inner member and the barrel.

8. A valve assembly substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

9. A hammer assembly substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

10. A probe substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.

11. An airgun provided with a valve assembly, and/or a hammer assembly and/or a probe according to any of the preceding claims.

12. An airgun having a compressed gas supply and means for releasing charges thereof into a barrel of the airgun in order to fire the pellet from the gun.

13. An airgun according to claim 12, further comprising any one or more of the features disclosed in the accompanying specification, claims, abstract and/or drawings, in any combination.

14. An airgun substantially as hereinbefore described with reference to Figures 4 and 5 of the accompanying drawings.