GB1592188A - Combustible fluid powered stapling or nailing apparatus - Google Patents

Description

(54) A COMBUSTIBLE FLUID POWDERED STAPLING OR NAILING APPARATUS (71) We, ANVAR-AGENCE NATIONALE DE VALORISATION DE LA RECHERCHE, a Public institution organised and existing under the laws of France, of 13 Rue Madeleine Michelis 92522 -Neuilly/Seine, France, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to machines intended for marking, nailing or stapling.

In this Specification, the relative terms "top" or "upper", and "bottom" or "lower" are used with reference to a machine positioned as shown in the accompanying drawings. However, it will be evident that the machine will function in any desired orientation.

In a known type of such machines there is included a percussion member adapted according to requirements and associated with an operating piston movable in a cylinder between an advanced position and a retracted position.

Various different ways of driving the operating piston have already been proposed; for example, systems which use compressed air as an energy source, devices driven by electricity, or the use of an explosive mixture introduced into the cylinder and adapted to effect the violent operation of the percussion member in such a manner that the latter operates effectively.

Our French Patent No. 1,229,671 describes a nailing or stapling machine of the type in which an explosive mixture is fired to produce the energy required to operate the percussion member of the machine.

On the whole, such machines have been found to give satisfactory results, but certain difficulties have been encountered in their industrial manufacture and their commercial distribution in the form of a model which is both competitive and perfectly reliable.

The present invention has as its object a machine of the kind in question whose production and utilisation are substantially simplified in comparison with known machines of this kind, the machines also being safe in operation.

According to the invention there its provided an apparatus for nailing, stapling or other fastener driving applications, including an elongate tubular member a cylinder head dividing the elongate tubular member into a first housing comprising a cylinder for a main operating piston, and a second housing for an auxiliary piston; a percussion member associated with the main operating piston which is adapted to move in the cylinder in said first housing; an auxiliary piston in said second housing adapted to move between top and bottom end of stroke positions, the auxiliary piston being held at the top end of stroke position at the beginning of each operating cycle and being arranged to drive the main operating piston to an intermediate position as it moves to its bottom end of stroke position, movement of the main operating piston to the intermediate position resulting in the generation of a space between the main operating piston and the cylinder head and the introduction of an explosive mixture into said space, the space generated having a determined volume dependent upon the stroke of the said auxiliary piston, the auxiliary piston also being arranged to store a chosen volume of combustible fuel when it is at its top end of stroke position and to transfer the fuel into the said space as it moves to its bottom end of stroke position, the transfer of fuel being effected with concomittant introduction of air into the said space in order to form the explosive mixture; ignition means adapted to ignite the explosive mixture when the auxiliary piston is at its bottom end of stroke position; means for evacuating exhaust gases formed after ignition of the explosive mixture; and means for actuating said ignition means.

According to a preferred embodiment of the invention, the auxiliary piston comprises internally, on one side of an axial valve known as the transfer valve, a metering chamber, and on the opposite side of the transfer valve, a buffer chamber which forms an intermediate volume between the combustion chamber and the metering chamber.

Preferably, the said transfer valve has a head which cooperates with a seat provided inside the auxiliary piston, and twooperat- ing rods extend from said transfer valve, one of which extends into the metering chamber for the purpose'of controlling a valve for admitting fuel into the metering chamber, while the other extends into the buffer chamber and controls the opening of the said transfer valve against the action of a calibrated spring by co-operation with the main operating piston.

According to a further preferred embodiment of the invention, a so-called front terminal portion of the auxiliary piston cooperates with a central depression in the main operating piston, which depression is provided with a plurality of oriented pas-, sages, while the said front terminal portion of the auxiliary piston is provided with suitably oriented passages, wliereby consid erable turbulence is created in the explosive mixture as it passes through the passages and the mixture is admitted into the com bustion chamber as a perfectly homogeneous mixture.

According to a further preferred embodiment of the invention, the buffer chamber contains a non-return valve which prevents burned gases from rising into the metering chamber.

The machine of the present invention is suitable for simple, economical production; its use is very simple because it is sufficient to operate a trigger or push-button to bring about a complete cycle of operation, while after operation the mechanism will resume its original position ready for a further complete cycle.

The machine is therefore practically permanently in operating condition.

These features are made possible essentially by the auxiliary piston which serves various main functions, namely: metering of a volume of gas when the piston is at its top end of stroke position; production of an explosive mixture . by admission of air when the auxiliary piston descends towards its bottom end of stroke position; formation of the explosive mixture in a combustion chamber which is generated upon the downward movement of the main piston, said downward movement of the main piston being caused by the auxiliary piston driving the main piston downwards; automatic return to the original locked position of the auxiliary piston as the result of the explosion in the combustion chamber.

It will be understood that the machine of the present invention is capable of various applications. Nevertheless, by way of example, the embodiment of the invention which is illustrated and described below is described by reference to a machine which is constructed and arranged to act as a stapling machine.

One embodiment of. a machine of the present invention will now be described, by way- of example qnly, with reference to the accompanying drawings, in which: Figure 1 shows an elevation'and partly in section a stapling machine according to the invention Figure 2 shows an élevåtíon, in section, of the operating mechanism for actuating the main piston- of Figure 1, including the auxiliary - piston, this mechanism being shown in the retracted or rest position; Figure 3 is a detailed' view on a larger scale and in section of the auxiliary piston of Figure 2; Figure 4 is a plan view of Figure 2;; Figures 5 to 8 are views similar to Figure 2, illustrating an operating cycle of the machine, Figures 9 and 10 are partial views of the" mechanism shown in Figure 2; and Figure 11 shows an alternátive construction of the rhain. operating piston.

In the embodiment illustrated in Figure 1, the machine comprises a part 10 forming a grippable handle and, associated with the latter, a longitudinal member 11 comprising in particular a percussion member and its operating mechanism.

The part 10 is arranged to accommodate additional parts, such as a gas reservoir 12, a pressure reducing valve 13 connected to the said gas reservoir, an ignition coil 14 connected electrically, on the one hand, to a source of energy in the form of batteries 15, and On the other hand to an electric circuit (not shown) leading to an'ignites 16 which can be seen in particular in Figures 2 to 7 and which is situated in the combustion chamber.

The part 10 also contains an operating push-button indicated generally by the reference 20, and is also adapted to form a magazine 21 for nails, staples, or the like 22, leading into a stapling head indicated gener- ally by 23 and forming a drivingin guide.

The longitudinal member 11 comprises a cylinder 25 closed at its ends by end pieces 26 and 27 respectively; internally the cylinder is equipped with a fixed cylinder head 28 and contains a main operating piston 29 with which a percussion member 30 is associated.

Between the main operating piston 29 and the end piece 27 the cylinder 25 contains a spiral spring 32 of which one end bears against the main piston 29 and of which the other end bears against the end piece 27; the main piston 29 is capable of rapid reciprocating axial displacement through the action of an operating mechanism indicated generally by 34. The mechanism 34 drives the main piston 29, and consequently the percussion member 30, from a first rest position to a second activated position in the course of which an article 22 is extracted from the magazine 21 and driven out of the stapling head, after which the spring 32 returns the main piston and percussion member to the first rest position so that they will be ready for a new cycle.

As shown more clearly in Figure 2, the operating mechanism 34, which is housed in an upper part of the cylinder 25, comprises an arrangement formed of a secondary or auxiliary piston 36, which is coaxial with the axis of the cylinder and with which a disc 37 is associated at the top part; the auxiliary piston is adapted to slide in a bore 38 provided in the cylinder head 28 and equipped with seals 38A, while a spring 39 interposed between the aforesaid disc 37 and the end piece 26 urges the said disc downwards. An actuator handle PA projectig out of the cylinder is associated with the disc 37 and consequently with the auxiliary piston 36, since the latter is connected to the disc; this handle is freely slidable through the disc because of holes provided for this purpose.

When the machine is at rest but activated, the various members are thus in the position shown in Figures 1 to 3. In these Figures the auxiliary piston 36 is in the upper end of stroke position; itis held in that position by a crutch 40 of spring material, connected at the bottom to the cylinder head 28. This crutch comprises (see in particular Figure 3) a stop abutment formed by a shoulder 40A having a sloping portion 40B adapted to cooperate with the disc 37; beyond this stop the crutch is provided with an extension 40C. On this extension is engaged a first sleeve 42 known as the bottom sleeve, which rests by a collar 42A on the disc 37, passing through a passage 26a provided in the cylinder end piece 26; the bottom sleeve 42 receives a second sleeve 43, known as the upper sleeve and having a collar 43A.A first spring 44 bears by its ends on these collars, which are disposed head to tail, while a second spring 45 is interposed between the collar 43A of the upper sleeve and the end piece 26 of the cylinder.

The first spring 44 serves to move the two sleeves 42 - 43 away from one another, while the purpose of the second spring 45 is to apply a thrust to the twb sleeves through the first spring 44, so that the sleeve 42 bears by its collar 42A against a corresponding face of the disc 37 when, as in the case shown in Figures 1 to 3, the auxiliary piston is in the upper end of stroke position.

It should be noted that the opening 26A provided in the end piece 26 of the cylinder and the opening 37a provided in the disc 37 for the passage of the extension 40C have a different function, which is to permit the admission of air into the cylinder in order to constitute an explosive mixture in the combustion chamber.

Externally, the end piece 26 of the cylinder is provided with a boss 26E which carries a movement transmission member in the form of a fork 50 mounted for pivoting about a pin 51 and having branches 51A, 51B extending on both sides of the said pin.

The branch 51A forms a control lever adapted to cooperate with the collar 43A of the upper sleeve 43, while at its free end portion the branch 51B has an opening 51C (Figure 4) for the passage of the end portion of the rod 55A of a valve indicated generally at 55.

This valve comprises in the usual manner a valve head 55B intended to cooperate with a seat 28A provided in the fixed cylinder head 28, while a passage 28B leading to the outside is likewise provided in this cylinder head for the evacuation of combustion gases.

The rod 55A therefore extends from the cylinder head 28, through which it passes, to a point beyond the outer face of the end piece 26; the valve 55 is urged into the closed position by means of a spring 58 interposed between a ring 59 and the branch 51B of the fork. A sleeve 60 is engaged on the rod 55A of the valve; its has a length such that one of its ends is in contact with the branch 51B of the fork 51, passing through apertures provided respectively in the disc 37 and in the end piece 26 of the cylinder, while the other end extends into the exhaust passage 28B. The exhaust valve 55 is therefore guided through the sleeve 60 at two points situated near the valve head and at the end portion of the valve rod.

In the exhaust passage 28B there is disposed an operating finger 65 (shown more clearly in Figures 1, 2 and 5 to 8) connected at one end to an operating lever 66 extending along the cylinder, while the other end is adapted to cooperate with the push-button 20.

The operating finger 65 is engaged by means of an end slot 65A on the valve rod near the valve head, between a shoulder 67 provided on the valve rod and the corres ponding end of the sleeve 60.

The push-button 20 (Figure 1) is associated by means of a screw 68 with a projection 69 provided on the cylinder 25 and is adapted to slide in the said projection; it is subjected to the action -of the spring 70 urging it downwards; a spring 71 is engaged on the lever 66, this spring being slightly more powerful than the spring 58 associated with the valve 55, and by one end it bears against an abutment 25A fixed laterally on the cylinder 25, while its other end bears against a terminal boss 66A of the lever 66, this boss being in addition intended to cooperate with the push-button 20.

Thus, starting from the push-button 20 the respective members 66, 65, 60, and 50 form an arrangement adapted to effect the release of the crutch 40 and the closure of the exhaust valve 55, these operations being effected simultaneously or with a slight time lag.

With regard to the auxiliary piston 36, this extends coaxially to the axis of the cylinder 25 and has a rear end portion coupled to the disc 37 and a front end portion facing the main operating piston 29.

At its rear end position the auxiliary piston 36 is connected, advantageously by necking-in, at 36A to a boss 37B provided for the purpose on a face of the disc 37.

Internally the boss 37B has a blind hole 37E in which, when the auxiliary piston is in its upper end of stroke position, a boss 26I is engaged which is provided on the bottom face of the end piece 26; a seal 37C is disposed in the hole 37E in order to provide sealing between the bosses 26I and 37B. In its interior the auxiliary piston has a first chamber C1, referred to hereinbelow as a metering chamber, which is separated from a second chamber C2, referred to as a buffer chamber, by a transfer valve having a valve head 70 adapted to cooperate with a seat 36D provided inside the auxiliary piston with the inter-position of a seal 36E.

Two operating rods 70A and 70B extend one on each side of the valve head 70; the rod 70A extends through the chamber C1 in the rear portion of the auxiliary piston, while the rod 70 B extends through the chamber C2 in the front portion.

The free end of the rod 70A is intended to cooperate with a corresponding end of the stem 75A of another valve, which is known as the admission valve and which is adapted to move axially inside the boss 26I and has a head 75 adapted to cooperate with a seat 75B provided in the end piece 26 of the cylinder.

The stem 75A of the said admission valve is mounted for sliding in the end piece 26 and in its boss 26I with the aid of a bore 26F,; it is also mounted for sliding in the boss 37B with the aid of a bore 37G. The bores 26F, 37B each have a longitudinally grooved inner surface adapted to form guide means for the rods of the transfer and admission valves while permitting the admission of fuel and outside air to the interior of the auxiliary piston. The admis- - sion valve 75 is in addition subjected to the action of a spring 76 urging it back onto its seat 75B.

It will be observed that the head 70 of the transfer valve is likewise subjected to the action of a spring 77 urging it back towards its seat 36D.

The buffer chamber C2 contains a valve, known as a non-return valve, with a seat 36G provided in a boss 36H inside the auxiliary piston, and also having a valve head 80 formed at the end portion of a bell-shaped part 80A adapted to slide on the rod 70B; the bell-shaped part 80A is subjected to the action of a spring 80B urging the valve head 80 onto its seat 36G.

It should be made clear at once that the spring 80B is weaker than the spring 77, which in turn is considerably weaker than the spring 76.

The front end portion of the auxiliary piston 36 is provided with distribution means for the explosive mixture, these means consisting of a plurality of holes 36I whose axes are directed in a selected manner.

The usefulness of an arrangement of this kind will be clear from the description of the operation of the machine.

As shown in Figure 11, the main operating piston 29 is provided in a central zone with a depression forming a circular bowj 29A into the interior of which a plurality of passages 29B lead, these passages being intended to establish communication between the said depression and a space E provided between the cylinder head 28 and the main operating piston 29.

At the centre of the depression 29A is provided a recess 29C adapted to cooperate with the, free end of the rod 70B.

The operation of the machine described above may be analysed as follows.

On starting up, the machine for example not being activated, the auxiliary piston 36 is in its lower end of stroke position; it is therefore necessary to bring the auxiliary piston 36 to its upper end of stroke position, for which purpose traction is applied (arrow F, Figure 2) to the actuator handle - PA.

After this operation the various members of the mechanism are as illustrated in Figure 2, that is to say: the main operating piston 29, and consequently the percussion member 30, are in the upper position, the upper position of the operating piston being determined by a circular ledge 25B provided inside the cylinder 25, so as to form the aforesaid space E between the main operating piston and the corresponding face of the cylinder head; the auxiliary piston 36 is in the upper end of stroke position, where it is retained by the associated crutch 40 locking the disc 37; the branch 51b of the fork 50 bears against the top of the boss 26E of the cylinder; the valve 55 is in the open 'position because the spring 71 is slightly more powerful than the spring 58 tending to close the valve; the admission valve 75 is opened by the operating rod 70A, thus permitting the admission through the passages 26F and 37G of a certain amount of fuel into the metering chamber C1, where it is confined because the transfer valve 70 is in the closed position due to the action of the spring 77; and no force is applied to the push-button 20.

When the push-button 20 is stressed in the direction of the arrow F2 (Figure 5), the position of the various members becomes as follows: the upward displacement of the finger 65 of the operating lever 66 brings about the displacement of the sleeve 60 in the direction of the arrow F3, which has the effect of: a) closing the valve 55 by means of the spring 58; b) causing the fork 50 to rock in the direction of the arrow F4.

As a result of the rocking of the fork 50 the branch 51a forming a control lever bears against the collar 43A of the upper sleeve 43, thus causing the displacement of the said sleeve (arrow F5) and also of the crutch 40 in the direction of the arrow F6; Displacement of the crutch and of its abutment 40A frees the disc 37 and consequently the auxiliary piston 36, which through the action of the spring 39 descends abruptly in the direction of the main piston 29, which is driven until the disc 37 bears against the cylinder head 28.

The displacement of the auxiliary piston 36 from its upper end of stroke position to its lower end of stroke position has the following effect (Figure 6): a) closing the admission valve 75 as soon as the disc 37 has moved away from the cylinder end piece 26, thus interrupting the feeding of fuel; b) moving the head 70 of the transfer valve away from its seat 36E because the end of the rod 70B has come into contact with the central depression 29C in the main operating piston 29;; c) effecting the transfer of the fuel from the metering chamber Cl to the aforesaid space E, which transfer is accomplished by the pressure of gaseous fuel in the metering chamber, the pressure causing the opening of the non-return valve 80 due to the fact that the spring 80B urging the valve into its closed position is very weak and therefore offers only negligible resistance, which is easily overcome by the pressure of the fuel in the metering chamber C1.

In Figure 6 the auxiliary piston is in its bottom end of stroke position and the space E' is filled with explosive mixture because in the course of the descent of auxiliary piston 36 the sealing between the end piece 36 and the disc 37 thereby permitting the admission of air from the surroundings into chambers C12 C2 and E. The incoming air which is sucked in by the descending auxiliary piston 36 has a scavenging effect given the negative pressure caused by the quick displacement of the auxiliary piston. The air enters the interior of the apparatus through passages 26A in the end piece 26, and passages 37A formed in the disc 37 and grooves 37G running through the disc 37.

A homogenous mixture of air and fuel is produced due to the air drawn in and the arrangement of the passages 36I, 29B respectively defined in the lower end of the auxiliary piston 36 and the depression 29A in the main operating piston 29 which causes considerable turbulence.

At this stage the auxiliary piston is in its lower position and the explosive mixture fills the space E' forming the combustion chamber; simultaneously, the bottom end of the percussion member 30 has come into contact with a projection 86A formed at one end of a retractable plate 86 inserted in the stapling head 23. The other end of the plate 86 is mounted for rocking at 86B, being subjected to the action of a spring 86C in an intermediate zone; the plate 86 is in the retracted position when the auxiliary piston is at the top end of its stroke through the action of a linkage (not shown) acting on the draw-bar 86D.

When the auxiliary piston 36 is in the lower end of stroke position and ignition circuit (known per se) produces a spark indicated at 90 (Figure 6), which brings about the explosion of the explosive mixture; this explosion of the explosive mixture in the combustion chamber has the effect (as shown in Figure 7) of:: a) pushing the non-return valve head 80 against its seat 36G in order to prevent the gases produced by the explosion from penetrating into the chambers C2 and C1; b) bringing about the rapid upward movement of the auxiliary piston 36 and locking it in its upper end of stroke position because the disc 37 is again bearing against the abutment 40A of the crutch 40 after the latter has been rocked through the action of the sloping surface 40B, and also because the percussion member is temporarily bearing against the return 86A of the element 86; c) unlocking the main piston 29 through the action of the plate 86 in response to the return of the auxiliary piston to its upper position (action on the draw-bar 86D).As a result, the main piston is pushed violently downwards (Figure 7) and drives the associated percussion member 30 against the action of the spring 32.

When the main piston has reached its bottom point (Figure 7) the article to be driven in (nail, staple, or other article) is expelled from the stapling head 23 and the main piston 29 then rises spontaneously to its original position through the, action of the spring 32.

In Figure 7 the auxiliary piston 36 has been shown in the course of its upward movement, while the main operating piston 29 is in its lower end of stroke position.

When the push-button 20 is released the valve 55 (Figure 8), which until that moment was in the closed position, is brought to the open position permitting the evacuation of the gases (arrow F8) to the outside by way of the passage 28B, this evacuation being assisted by the rising of the main piston.

One operating cycle having been completed, all the parts are in the rest position for a new cycle, that is to say in the position shown in Figure 1.

Entirely automatic operation, one stroke after the other, is thus obtained.

It should be noted that if the user were to maintain pressure on the push-button 20 for too long a time, the interlocking of the auxiliary piston 36 in its upper end of stroke position is not thereby prevented.

Assuming in fact that the fork 50 is held in the rocked position by pressure of the push-button, as shown in Figures 9 and 10, the disc 37 will nevertheless reengage by bearing against the abutment 40A owing to the fact that at the end of the upward movement of the auxiliary piston, the sleeves 42, 43, which were bearing against this abutment (Figure 7), are pushed upwards by the disc 37; since the branch 51A of the fork 51 is not retracted, the collar 43A of the upper sleeve 43 will come to bear against the bottom face of the branch 51A, which has the effect of slightly compressing the spring 44.

When the fork 50 is freed (pressure ceases on the push-button 20) it resumes its original position by rocking in the direction of the arrow F7 (Figure 9), which has the effect of releasing the collar 43A of the sleeve 43 which, being thus in turn freed, also returns to its original position under the action of the spring 44.

It should be observed that as long as the fork 50 has not returned to its original position a cycle cannot be commenced owing to the fact that action on the pushbutton 20 would have no effect on the fork 50, which would remain in the position shown in Figure 9.

Furthermore, in the event of pressure on the button being released before the end of the operating cycle, this cycle would not be disturbed thereby although the exhaust valve would be urged to its open position.

The volume of explosive mixture contained in the chamber E' and the small space provided between the head 55B of the exhaust valve and its seat 28A are in fact such that as soon as firing has been effected the valve head is subjected to pressure such that it is closed, pushing back the operating finger 65, so that the boss 66A of the push-button is accordingly moved away to the rest position.

As can be seen in Figure 11, the main operating piston 29 may be provided with one or more passages 29E for the introduction of additional air to the combustion chamber; these passages are closed on the side situated towards the cylinder head by a deformable flat seal 90 disposed in a circular groove 29F and secured by a circlip 91.

The introduction of additional air into the combustion chamber is effected in the course of the operating phase during which under the action of the axial displacement of the auxiliary piston 36 the main operating piston 29 passes from its upper end of stroke position (Figure 5) to its lower end of stroke position (Figure 6) in which the space E' forms the combustion chamber into which the explosive mixture is admitted.

In the course of the displacement of the main piston 29 the flat seal 90 is in fact deformed by the thrust of the air situated between the main operating piston and the cylinder end piece 27, which is able to bring the compartment accommodating the spring 32 into communcation with the atmosphere.

WHAT WE CLAIM IS: 1. An apparatus for nailing, stapling or other fastener driving applications, including an elongate tubular member; a cylinder head dividing the elongate tubular member into the first housing comprising a cylinder for a main operating piston, and a second housing for an auxiliary piston; a percussion member associated with the main operating piston which is adapted to move in the cylinder in said first housing; an auxiliary piston in said second housing adapted to move between top and bottom end of stroke positions, the auxiliary piston being held at the top end of stroke position at the beginning of each operating cycle and being arranged to drive the main operating piston to an intermediate position as it moves to its bottom end of stroke position, movement of the main operating piston to the intermediate position resulting in the generation of a space between the main operating piston and the cylinder head and the introduction of an explosive mixture

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (27)

**WARNING** start of CLMS field may overlap end of DESC **. return of the auxiliary piston to its upper position (action on the draw-bar 86D). As a result, the main piston is pushed violently downwards (Figure 7) and drives the associated percussion member 30 against the action of the spring 32. When the main piston has reached its bottom point (Figure 7) the article to be driven in (nail, staple, or other article) is expelled from the stapling head 23 and the main piston 29 then rises spontaneously to its original position through the, action of the spring 32. In Figure 7 the auxiliary piston 36 has been shown in the course of its upward movement, while the main operating piston 29 is in its lower end of stroke position. When the push-button 20 is released the valve 55 (Figure 8), which until that moment was in the closed position, is brought to the open position permitting the evacuation of the gases (arrow F8) to the outside by way of the passage 28B, this evacuation being assisted by the rising of the main piston. One operating cycle having been completed, all the parts are in the rest position for a new cycle, that is to say in the position shown in Figure 1. Entirely automatic operation, one stroke after the other, is thus obtained. It should be noted that if the user were to maintain pressure on the push-button 20 for too long a time, the interlocking of the auxiliary piston 36 in its upper end of stroke position is not thereby prevented. Assuming in fact that the fork 50 is held in the rocked position by pressure of the push-button, as shown in Figures 9 and 10, the disc 37 will nevertheless reengage by bearing against the abutment 40A owing to the fact that at the end of the upward movement of the auxiliary piston, the sleeves 42, 43, which were bearing against this abutment (Figure 7), are pushed upwards by the disc 37; since the branch 51A of the fork 51 is not retracted, the collar 43A of the upper sleeve 43 will come to bear against the bottom face of the branch 51A, which has the effect of slightly compressing the spring 44. When the fork 50 is freed (pressure ceases on the push-button 20) it resumes its original position by rocking in the direction of the arrow F7 (Figure 9), which has the effect of releasing the collar 43A of the sleeve 43 which, being thus in turn freed, also returns to its original position under the action of the spring 44. It should be observed that as long as the fork 50 has not returned to its original position a cycle cannot be commenced owing to the fact that action on the pushbutton 20 would have no effect on the fork 50, which would remain in the position shown in Figure 9. Furthermore, in the event of pressure on the button being released before the end of the operating cycle, this cycle would not be disturbed thereby although the exhaust valve would be urged to its open position. The volume of explosive mixture contained in the chamber E' and the small space provided between the head 55B of the exhaust valve and its seat 28A are in fact such that as soon as firing has been effected the valve head is subjected to pressure such that it is closed, pushing back the operating finger 65, so that the boss 66A of the push-button is accordingly moved away to the rest position. As can be seen in Figure 11, the main operating piston 29 may be provided with one or more passages 29E for the introduction of additional air to the combustion chamber; these passages are closed on the side situated towards the cylinder head by a deformable flat seal 90 disposed in a circular groove 29F and secured by a circlip 91. The introduction of additional air into the combustion chamber is effected in the course of the operating phase during which under the action of the axial displacement of the auxiliary piston 36 the main operating piston 29 passes from its upper end of stroke position (Figure 5) to its lower end of stroke position (Figure 6) in which the space E' forms the combustion chamber into which the explosive mixture is admitted. In the course of the displacement of the main piston 29 the flat seal 90 is in fact deformed by the thrust of the air situated between the main operating piston and the cylinder end piece 27, which is able to bring the compartment accommodating the spring 32 into communcation with the atmosphere. WHAT WE CLAIM IS:

1. An apparatus for nailing, stapling or other fastener driving applications, including an elongate tubular member; a cylinder head dividing the elongate tubular member into the first housing comprising a cylinder for a main operating piston, and a second housing for an auxiliary piston; a percussion member associated with the main operating piston which is adapted to move in the cylinder in said first housing; an auxiliary piston in said second housing adapted to move between top and bottom end of stroke positions, the auxiliary piston being held at the top end of stroke position at the beginning of each operating cycle and being arranged to drive the main operating piston to an intermediate position as it moves to its bottom end of stroke position, movement of the main operating piston to the intermediate position resulting in the generation of a space between the main operating piston and the cylinder head and the introduction of an explosive mixture

into said space, the space generated having a determined volume dependent upon the stroke of the said auxiliary piston, the auxiliary piston also being arranged to store a chosen volume of combustible fuel when it is at its top end of stroke position and to transfer the fuel into the said space as it moves to its bottom end of stroke position, the transfer of fuel being effected with concomittant introduction of air into the said space in order to form the explosive mixture ignition means adapted to ignite the explosive mixture when the auxiliary piston is at its bottom end of stroke position; means for evacuating exhaust gases formed after ignition of the explosive mixture; and means for actuating said ignition means.

2. Apparatus according to Claim 1, wherein the auxiliary piston is slidably mounted in the second housing, and has internally at least one metering chamber for receiving the fuel, which chamber, when the said auxiliary piston moves from its top end of stroke position to its bottom end of stroke position, is brought into communication with the atmosphere in order to form the explosive mixture by being swept with the air drawn in.

3. Apparatus according to Claim 1 or Claim 2, wherein the auxiliary piston, which is coaxial with the cylinder, has internally two chambers set apart axially, and in communication with each other via a trans after valve, of which one is the metering chamber and is situated on the side of the transfer valve remote from the main operat ingpiston, and of which the other is a buffer chamber and is situated on the side of the transfer valve closest to the main operating piston, the said transfer valve being displaceable axially between a closed position in which the two chambers are isolated one from the other when the auxiliary piston is held at the top end of stroke position, and an open position in which the said chambers are brought into communication when the auxiliary piston moves to its bottom end of stroke position, the transfer valve being in addition adapted to control a fuel supply valve for controlling the supply of combustible fuel to the metering chamber, nonreturn valve means also being provided in the said buffer chamber.

4. Apparatus according to Claim 3, wherein the transfer valve has a valve head adapted to cooperate with a seat provided inside the auxiliary piston, two axial operat ing rods extending one on each side of the said head, one into each of the metering and buffer chambers.

5. Apparatus according to Claim 4, wherein the free end of the axial operating rod which extends into the metering chamber is adapted to cooperate with the fuel supply valve which is accommodated in an upper cylinder end piece so as to open the fuel supply valve whilst the auxiliary piston is in its top end of stroke position.

6. Apparatus according to Claim 4 or Claim 5, wherein the free end of the operating rod which extends into the buffer chamber is adapted to cooperate with the main operating piston to open the transfer valve when the auxiliary piston is pressed against the main operating piston.

7. Apparatus according to any one of Claims3 to 6, wherein the non-return means disposed in the buffer chamber consists of an axial displacement valve.

8. Apparatus according to Claim 7, wherein the non-return valve has a seat arranged internally in the auxiliary piston for a bell-shaped valve head which is mounted for sliding on the said operating rod and is urged into the closed position by a calibrated spring.

9. Apparatus according to any one of the preceding claims, wherein a front end portion of the auxiliary piston is intended to cooperate with the main operating piston, the front end portion having a series of passages adapted to bring the interior of the said auxiliary piston into communication with the said space between the said cylinder head and the main operating piston.

10. Apparatus according to Claim 9, wherein the said passages have their respec- tive axes so oriented as to create turbulent fow of a fluid passing through said passages.

11. Apparatus according to any one of the preceding claims, wherein the face of the main operating piston facing the cylinder head has a central depression having a plurality of passages adapted to bring the said depression into communication with the said space forming a combustion chamber between the cylinder head and the main piston, these passages having their respective axes so oriented as to create turbulent flow of fluid passing therethrough whereby the explosive mixture is intimately mixed on passage into the said space.

12. Apparatus according to any one of the preceding claims, wherein the main operating piston has passages for admission of air to said space, these passages being adapted to be closed by a deformable seal.

13. Apparatus according to any one of the preceding claims, wherein the auxiliary piston has a rear portion on the fuel supply side, which has a bore which, when the auxiliary piston is in its top end of stroke position, fits sealingly over a boss provided in the upper cylinder end piece.

14. Apparatus according to any one of the preceding claims, wherein the auxiliary piston is held at the top end of stroke position by retaining means comprising a disc associated with the rear portion of the auxiliary piston and subjected to the action of a spring which urges it towards the main operating piston, and a crutch movable between an operative position in which the disc is locked and the spring compressed so that the auxiliary piston is held in the upper end of stroke position, and a retracted position in which the said auxiliary piston is freed and urged in the direction of its lower end of stroke position through the action of the said spring.

15. Apparatus according to Claim 14, wherein the cylinder head carries the said crutch, the ignition means and also an exhaust valve for the evacuation of the combustion gases.

16. Apparatus according to Claim 15, wherein the crutch is moved from its operative position to its retracted position and the exhaust valve is operated for opening and closing by means of an arrangement adapted to effect conjointly the operation of the crutch and the operation of the said exhaust valve with the aid of the same operating member.

17. Apparatus according to Claim 16, wherein the said arrangement comprises, associated with an operating push-button, an operating finger of which a terminal portion is engaged on a rod of the exhaust valve between a collar, which is provided thereon and set back in relation to the valve head, and one end of a sleeve surrounding the said valve rod, this sleeve being in contact by its other end with a transmission member installed between the valve stem and a corresponding end portion of the crutch.

18. Apparatus according to Claim 17, wherein the exhaust valve rod has a spring urging it back to the closed position, while the push-button is subjected to the action of at least one spring acting against the spring of the said valve, the valve spring being weaker than the spring associated with the push-button.

19. Apparatus according to Claim 16 or Claim 17, wherein the spring associated with the exhaust valve cooperates with the transmission member in order to urge the latter back to an inoperative position and at the same time to urge the exhaust valve back to the closed position.

20. Apparatus according to any one of Claims 16 to 19, wherein the transmission member is formed by a fork having two branches extending one on each side of a pivot carried by the upper cylinder end piece, a first branch of the transmission member being captive between the valve spring and the sleeve on the rod of the exhaust valve and a second branch being shaped to cooperate with means associated with the crutch.

21. Apparatus according to Claim 20, wherein the crutch is formed by a rod of resilient material, of which one end is fixed to the cylinder head while the other end has means adapted to press against the said second branch of the transmission member.

22. Apparatus according to Claim 21, wherein the means adapted to press against the said second branch of the transmission member comprises two sleeves which have collars, the sleeves being engaged head to tail on the crutch and between which a spring is supported on the collars, the upper sleeve, which cooperates with the said second branch of the transmission member, being subjected to the action of an elastic means.

23. Apparatus according to Claim 22, wherein the upper cylinder end piece supports the transmission member and has orifices for the passage of the rod of the exhaust valve and for permitting the movement of the engaged sleeves on the crutch, these passages constituting apertures for admission of air which eventually forms the explosive mixture.

24. Apparaus according to any one of Claims 3 to 23, wherein the fuel supply valve is disposed in a chamber in the upper cylinder end piece, the chamber being in communication with a coaxial fuel supply, the opening and closing of the fuel supply valve being controlled by movement of the auxiliary piston from its top end stroke position to its bottom end stroke position.

25. Apparatus according to any one of the preceding claims, in which the longitudinal member is associated with a grippable handle which houses a reserve of fuel, such as gas, a pressure reducing valve, a series of batteries, a coil connected to the batteries, and a magazine for articles to be ejected from the apparatus, the said magazine leading into a guide for the articles to be ejected.

26. Apparatus according to Claim 25, wherein the ejection guide houses a retractable resilient plate adapted to offer resistance to the percussion member when the auxiliary piston is not in the upper end of stroke position.

27. Apparaus according to claim 1 substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.