EP3067158B1 - Improvements to a gas-powered fastening tool - Google Patents

Description

TECHNICAL AREA

The invention relates to improvements for a gas fastening tool and a gas fastening tool comprising at least one of these improvements.

STATE OF THE ART

The state of the art includes the documents EP-B1-123 717 , EP-B1-1 243 383 , EP-B1-2 087 220 , EP-A2-1 371 457 , EP-A2-1 375 074 , EP-A2-1484138 and US-A1-2006 / 226193 .

Sealing or fixing tools, called gas tools, are tools comprising an internal combustion engine operating by firing a fuel-air mixture in a combustion chamber, the fuel being injected into the chamber by a device injection from a fuel cartridge. Such tools are intended to drive fasteners in support materials (such as wood, concrete or steel) to fix parts. Gas tools are now widespread and can be used to install fasteners such as staple, nail, point, pin, etc. As fuel for an internal combustion engine, there may be mentioned for example gasoline, alcohol, in liquid form and / or gas.

In general, such a tool is portable and comprises a housing in which is mounted the propulsion internal combustion engine of a driving piston of a fastener. Such a tool may also include a battery power supply and a handle, handling and shooting on which is mounted a detent actuating the tool.

The present invention provides improvements to this technology.

SUMMARY OF THE INVENTION

The invention relates to combustion chambers or pre-combustion chambers for a gas fastening tool, comprising a casing defining a combustion cavity having a generally elongate shape of longitudinal axis X, and a second combustion cavity, ignition means , such as a spark plug, being situated at a longitudinal end of said first cavity and a longitudinal end of said first cavity, opposite said ignition means, being in fluid communication with said second cavity, characterized in that said first cavity has a variable cross section along said X axis, said first cavity having a generally stepped shape and comprising at least a first cross section portion S1 and a second cross section portion S2, with S1 less than S2, said ignition means being located in said first portion.

The invention can thus reduce the size of the chamber, for example by reducing its length. This reduction in length can reduce the travel time required for the flame to cross the chamber longitudinally, thereby reducing the time of a firing cycle by the tool. The invention can further optimize the spatial distribution of the mass of the chamber inside the tool, for example to move the center of gravity of the tool in a predetermined area.

• le ratio S2/S1 est par exemple compris entre 1,1 et 3,0 voire plus ; dans un cas particulier, il peut être compris entre 1,1 et 1,5, et de préférence entre 1,2 et 1,5,
• ladite cavité a en section longitudinale une forme générale en L ou T,
• ladite cavité a au moins en partie une forme sphérique ou ovoïde,
• ledit carter définit trois ouvertures dont deux sont alignées sur un même axe U et une troisième est alignée sur un axe Y sensiblement perpendiculaire à l'axe U,
• ledit carter comprend une première demi-coque comportant une première paroi en portion de sphère,
• ladite première paroi est une paroi médiane qui est située entre deux parois d'extrémité chacune en portion de cylindre,
• lesdites parois d'extrémité définissent en partie lesdites ouvertures d'axe U,
• ledit carter comprend une seconde demi-coque comportant deux parois d'extrémité chacune en portion de cylindre et définissant en partie lesdites ouvertures d'axe U, et une paroi cylindrique définissant ladite ouverture d'axe Y,
• lesdites chambres comportent un carter définissant un logement dans lequel est monté et peut coulisser un piston pour l'entraînement d'un élément de fixation, ledit piston étant configuré pour être déplacé en translation dans ledit logement depuis une position de repos jusqu'à une position de travail, ledit logement étant en communication fluidique avec ladite second cavité.

The chamber according to the invention may comprise one or more of the following characteristics, taken separately from one another or in combination with each other:

• the ratio S2 / S1 is for example between 1.1 and 3.0 or more; in a particular case, it may be between 1.1 and 1.5, and preferably between 1.2 and 1.5,
• said cavity has in longitudinal section a general shape in L or T,
• said cavity has at least partly a spherical or ovoid shape,
• said housing defines three openings, two of which are aligned on the same axis U and a third is aligned on a Y axis substantially perpendicular to the axis U,
• said casing comprises a first half-shell comprising a first wall in a portion of a sphere,
• said first wall is a median wall which is located between two end walls each in a portion of a cylinder,
• said end walls partially define said U-axis apertures,
• said housing comprises a second half-shell comprising two end walls each in cylinder portion and partially defining said U-axis apertures, and a cylindrical wall defining said Y-axis aperture,
• said chambers comprise a housing defining a housing in which is mounted and slidable a piston for driving a fixing element, said piston being configured to be displaced in translation in said housing from a rest position to a position said housing being in fluid communication with said second cavity.

The present invention also relates to a gas fastening tool, comprising a chamber or several chambers as described above, and / or a device as defined above.

BRIEF DESCRIPTION OF THE FIGURES

• la figure 1 est une vue schématique d'un outil de fixation à gaz selon l'invention,
• la figure 2 est une vue schématique d'un dispositif d'injection d'un gaz combustible,
• la figure 3 est une vue schématique en perspective du dispositif de la figure 2,
• les figures 4a et 4b sont des vues schématiques correspondant à la figure 2 et montrant respectivement deux positions d'un organe d'actionnement du dispositif,
• la figure 5 est une vue schématique en coupe axiale de chambres d'un outil de fixation à gaz selon l'art antérieur,
• les figures 6 à 8 sont des vues schématiques en coupe axiale de chambres d'un outil de fixation à gaz, les figures 6 et 7 illustrant l'invention,
• les figures 9a à 9c sont des vues schématiques en perspective et/ou en coupe axiale d'une chambre de combustion,
• les figures 10a à 10e sont des vues schématiques en coupe axiale d'une chambre de travail.

The invention will be better understood and other details, characteristics and advantages of the present invention will appear more clearly on reading the description which follows, given by way of non-limiting example and with reference to the accompanying drawings, in which:

• the figure 1 is a schematic view of a gas fastening tool according to the invention,
• the figure 2 is a schematic view of a device for injecting a combustible gas,
• the figure 3 is a schematic perspective view of the device of the figure 2 ,
• the Figures 4a and 4b are schematic views corresponding to the figure 2 and showing respectively two positions of an actuating member of the device,
• the figure 5 is a schematic view in axial section of chambers of a gas fastening tool according to the prior art,
• the Figures 6 to 8 are schematic views in axial section of chambers of a gas fixation tool, the figures 6 and 7 illustrating the invention,
• the Figures 9a to 9c are schematic views in perspective and / or in axial section of a combustion chamber,
• the Figures 10a to 10e are schematic views in axial section of a working chamber.

DETAILED DESCRIPTION

The tool 10 shown on the figure 1 comprises a housing 12 in which there is an internal combustion engine 14, with a combustion chamber for containing a mixture of air and fuel whose ignition causes the propulsion of a piston intended to drive a fastener element extracted from a feed magazine 16, the fastener being adapted to be anchored in a support material, at the outlet of a guide-tip 18 extending to the front of the housing 12. All these components gas fastening tools are well known to those skilled in the art and therefore they have not all been represented in the drawing.

The tool housing has an axis 20 along which the drive piston moves and in the tip guide 18 the fasteners.

The tool comprises a handle 22 for gripping and handling the tool. It extends, from the housing and outside thereof, substantially perpendicular to the axis 20, slightly inclined on it according to the application of the tool and the ergonomics during use. The handle 22 is also used for firing, by an actuation trigger 24 mounted on it, in the zone 26 of its connection to the housing 12.

The fuel supply to the combustion chamber of the engine 14 is effected by means of an injection device 28 from a cartridge 30 of combustible gas.

Advantageously, the injection device 28 and the cartridge 30 are housed in an arm 32 connected to the housing 12, which extends substantially perpendicular to the axis 20, in front of the handle 22, and in which the magazine 16 is also provided.

Another arm 34 extends substantially parallel to the axis 20, between the handle 22 and the arm 32, so as to form a bridge between the two, the (lower) side opposite the housing 12.

Various features will now be described that can be integrated, independently of each other or in combination with each other, into tool 10 of the present invention. figure 1 .

Injection device

Features are illustrated by the figure 2 and relate to the device 28 for injecting fuel into the engine from a fuel cartridge 30.

The fuel is in the liquid state in the cartridge and must be evaporated, the fuel gas being intended to be mixed with air before being burned in the combustion chamber of the engine.

An injection device of a gas fixation tool must thus allow the evaporation of the fuel.

The document EP-B1-2 087 220 discloses a liquid fuel supply and evaporation system for converting a liquid fuel to a gaseous fuel. This system comprises an evaporator element associated with a heated casing for heating the evaporator element. The evaporator element is made of sintered metal and has a generally conical or frustoconical shape.

This technology is complex and relatively bulky, in particular because of the particular shape of the evaporator element. This technology is also relatively expensive.

In addition, this evaporator element is relatively fragile and has a low resistance to vibrations and shocks generated during the operation of a fixing tool. In addition, since the fuel used to operate these tools may contain lubricants, additives, or even impurities, the evaporator element can get clogged thereby blocking the passage of fuel through it. The result of this situation is the malfunction of the tool, which requires disassembly and cleaning of the evaporator element and possibly its replacement because the cleaning operation can damage this element.

All the above mentioned problems can be solved by the device. While attempting to manage the clogging of the evaporator element, there is provided a filter element having in particular the purpose of trapping the various materials contained in the fuel leaving the cartridge.

Different filters have been tested. The filters consist essentially of a screen, a lattice, a grid, a fabric, a fabric, a foam, or fibers. These filters are made of metal or plastic, or from mineral or natural fibers. The purpose of these filters is to trap the particles contained in the fuel while allowing the fuel to flow through the filter.

In order to simplify the prior art injection device, the evaporator element is removed. Surprisingly, the use of a filter arranged in the simplified injection device, combined with an evaporation cavity, makes it possible to optimally vaporize the fuel for the purpose of feeding the combustion chamber of the combustion chamber. tool.

The figure 2 represents an embodiment of the injection device 28.

A valve 40 for calibrating a quantity of liquid fuel is interposed between the liquid fuel cartridge 30 and the simplified evaporator unit 42. A filter 44 is disposed in a housing or bore 46 provided in the block 42. A predetermined quantity of liquid fuel is discharged from the cartridge 30 through the valve 40 into the block 42, passing through the filter 44, and arrives in the evaporation cavity 47. The block 42 is made of a heat-conducting material, such as metal. The liquid fuel flowing through the filter 44 is at least partially converted to gaseous fuel by the heat input of the ambient medium, which transmits calories to the evaporator block 42.

Downstream of the filter 44 and the cavity 47, the at least partially vaporized fuel continues to circulate in the block 42, and absorbs additional heat from the environment. The downstream portion of the block 42 includes an evaporation line 48, acting as a distribution manifold, to the combustion chamber 50 of the attachment tool.

The sizing parameters of the device 28, and in particular of the cavity 47 and the pipe 48, such as the length, the diameter, the thickness, etc., are designed so that the fuel is entirely converted into the outlet of a downstream discharge orifice 51 of the pipe 48. To help transfer heat from the surrounding medium, the block 42 and / or the pipe 48 may optionally comprise one or more fins 52 disposed at least on one of their surfaces. .

Leaving the discharge orifice 51, the gaseous fuel can be directly injected into the combustion chamber 50. As an option, the gaseous fuel leaving the discharge orifice 51 can supply one or more fuel outlet nozzles 54 and The combustible gas may alternatively supply a jet pump 56 of the venturi type, into which ambient air is entrained in the jet pump 56, and mixed with the gaseous fuel injected by the jet fuel. or the nozzles 54, so as to form an air-fuel mixture for feeding the combustion chamber 50.

This evaporator block 42 is therefore easier to manufacture and less expensive. The filter is flat and therefore relatively simple. It extends substantially in a plane parallel to the axis Z of the cartridge 30. It has for example a form of pellet, disk or block. It is much simpler and less fragile than the complex parts used in the prior art. Therefore, the simplified evaporator block is also easier to maintain when needed, although the need for maintenance of such a block is also significantly reduced.

The figure 3 is a schematic perspective view of device 28 of the figure 2 and shows in particular that the pipe 48 is formed in one piece with a part of the evaporator block 42.

As we see in figure 2 , the pipe 48 has a general shape of S or L. The cavity 47 has a T-shaped section whose upstream portion of larger transverse dimension forms the housing 46 for receiving the filter. The cavity 47 communicates with a rectilinear end portion of the pipe 48. The pipe comprises another rectilinear end portion which defines the discharge orifice 51. These two portions are parallel and connected to each other by a median rectilinear portion of the duct, which extends substantially parallel to the longitudinal axis Z of the cartridge 30. This rectilinear portion may be closed sealingly by a screw at its connection to the straight end portion which defines the discharge port 51.

The evaporator block 42 comprises a bore in which is mounted and slidable, along the longitudinal axis Z of the cartridge 30, an actuating member 58. This actuating member has a rectilinear elongated shape and comprises an internal bore. 60. This bore comprises a first axial portion which extends along the member 58 and opens at the lower end thereof, and a radial portion which extends between the end upper axial portion and the periphery of the organ. The outlet of this radial portion is located next to the filter 44.

The member 58 is movable between two positions: a high position or rest represented at the figure 4a and a low or working position represented at the figure 4b . In both cases, the aforementioned radial outlet of the bore is located opposite the filter 44. Seals are provided between the member 58 and the bore in which it is mounted.

The lower end of the member 58 is configured to cooperate by interlocking with a connecting end of the cartridge 30.

The displacement of the member 58 from its rest position to its working position causes the release of a calibrated quantity of fuel from the cartridge 30. This fuel, in liquid form, circulates in the bore 60 of the member 58 and passes through the filter 44, which retains any impurities, before entering the cavity 47 in which is initiated the conversion of the liquid fuel gaseous fuel. The fuel circulates in the pipe 48 to complete its evaporation and arrives in the gaseous state at the nozzle 54. It is then sprayed into the jet pump 56 and mixed with air which enters the pump by venturi effect. the air-fuel mixture is then injected into the chamber 50 of the engine.

Advantageously, and as represented at figure 2 , the block 42 is located above the cartridge 30, the pipe 48 extends partly on one side of the cartridge, and the jet pump 56 has an orientation substantially perpendicular to the longitudinal axis Z of the or cartridge 48. Ideally, the cartridge 30, the block 42 and the pipe 48 are housed in the arm 32 and the jet pump extends in the arm 34, the combustion chamber 50 then being housed in the handle 22 of the tool of the figure 1 .

The filter 44 has for example a permeability less than 50 darcy and preferably between 10 to 33 darcy, which allows to filter particles with a diameter of between 7 .mu.m and 14 .mu.m, with an efficiency of 98 to 99.9%.

Pre-combustion chamber

A heat engine of a gas fastening tool comprises a combustion chamber and a working chamber in which a driving piston of a fastener is able to move under the effect of the explosion of the air mixture. -combustible in the combustion chamber.

Advantageously, as shown in figure 5 which represents the prior art described in the document EP-B1-1 243 383 the engine comprises a pre-combustion chamber 60 and a combustion chamber 50. The first combustion chamber or pre-combustion chamber 60 initiates the combustion of the air-fuel mixture. This chamber 60 comprises a housing 62 which defines a combustion cavity 64 in which ignition means such as a spark plug 65 are mounted.

The chambers 60, 50 are separated from one another by a valve 66. Pre-combustion of the mixture in the chamber 60 causes an increase in pressure in the cavity 64. When this pressure exceeds a certain threshold, the valve opens and passes the fuel mixture through the chamber 50.

The chamber 50 comprises a casing 68 defining a combustion cavity 70. The mixture arrives in the chamber 50 with a relatively high pressure. The flame from the chamber 60 reaches the chamber 50, the combustion at high pressure in the chamber 50 to improve the performance of the tool. The combustion 50 in the chamber causes an increase in pressure in the cavity 70, which forces the piston 78 to move in the working chamber 80.

As can be seen from figure 5 , it is known to provide a pre-combustion chamber 60 of elongated shape, a longitudinal end of which is connected to the combustion chamber 50, and whose opposite longitudinal end comprises the spark plug 64.

The output power of the combustion chamber 50 can be increased up to fifty percent (50%) simply by extending the precombustion chamber 60.

In the document EP-B1-1 243 383 the precombustion chamber 60 has a predetermined length B and a predetermined width A, in which the length B is substantially greater than the width A. More particularly, the ratio of the length B to the width A, known as the ratio or ratio the appearance of the precombustion chamber 60, is at least 2: 1, and can be much larger with an optimum around 10: 1 according to the same document.

It was also indicated in the document EP-B1-1 243 383 discontinuities or irregularities present in or on the internal surfaces of the precombustion chamber should be avoided due to the fact that such structures tend to degrade the power of the engine. In addition, a pre-combustion chamber may have a round, oval shape, rectangular, or other, in cross section, as long as its length is greater than its width.

Therefore, the pre-combustion chamber 60 of the prior art has a relative elongation B which is detrimental for the tool in terms of size.

Another disadvantage of this pre-combustion chamber 60 is that the longer the precombustion chamber, the longer the delay between the ignition of the spark and the ignition of the combustion chamber 50 is important. This can increase the duration of the firing cycle of the tool, which is problematic for some fastening applications.

Finally, the design of the pre-combustion chamber 60 is not optimal in terms of ergonomics.

The improvements below make it possible to optimize the size of the tool, to optimize its operation, and / or to shorten the duration of a firing cycle and in particular the duration between the ignition of the pre-combustion chamber. 60 and combustion in the chamber 50 while maintaining good performance of the combustion chamber.

To be able to compare the effect of the new precombustion chamber design vis-à-vis the prior art, the inventors have kept the total volume of the chambers 50, 60 constant. Thus, the total quantities of air mixture -combustible are comparable, and therefore the same total amounts of raw energy are available.

The volume of the pre-combustion chamber 60 is designated V1, and the main volume of the combustion chamber 50 is V2. V1 + V2 is constant for all the tests. In addition, as the aim is to improve the performance of the pre-combustion chamber 60, V1 is kept the same for all the exemplary embodiments.

It is found that, keeping V1 constant, an interesting effect has been achieved by changing the configuration of the precombustion chamber 60 from an elongated shape of constant cross-section to an elongated shape whose cross section varies along the longitudinal axis of the bedroom. It may have a cross section that is staggered or has a frustoconical shape.

This preferably means that the pre-combustion chamber has, from the spark plug 65, in the direction of the combustion chamber 50, an increasing section. Preferably, the pre-combustion chamber 60 has two parts, the first part having the spark plug 65 and having a first maximum inside diameter which is smaller than the minimum inside diameter of the second part.

Preferably, at least one diameter, and preferably both diameters of the first and second portions are constant. According to an exemplary embodiment of the invention, as represented on the figure 6 , the elongate chamber of constant cross section is replaced by two portions, one upper, has a larger cross section S2 than S1 of the other, lower. The chamber 60 thus has a generally T-shaped longitudinal section. Consequently, while keeping the volume V1 constant, this embodiment has a length less than the length B of the prior art. As a result, the size of the tool can be reduced.

The reduction of the length of the pre-combustion chamber 60 makes it possible to reduce the distance between the spark plug 65 and the combustion chamber 50, which has the advantage of reducing the ignition time of the chamber 50, as well as the overall duration of the a shooting cycle.

The invention thus provides an effective precombustion chamber for a tool that is less bulky and can operate faster than those of the prior art.

The figure 7 shows an alternative embodiment of the precombustion chamber 60. This figure shows a precombustion chamber 60 which has a portion having a horizontal extension component forward, so that the shortest fluid flow line between the spark plug 65 and the connection to the combustion chamber 50a (at least partly) a horizontal component inclined towards the rear of the tool, coming from the spark plug.

This design leads to better ergonomics because it is more beneficial in terms of tool balance. With this design, the pre-combustion chamber is no longer located entirely on one side of the tool so that the combustion chamber and the working chamber 80 do not necessarily form a conventional L-shaped architecture, that is, say a tool similar to a "gun".

This new design is more practical in terms of ergonomics since the masses of the working chamber and the magazine with the fixing elements are no longer all located on the same side of the tool and on the same side of the handle of the tool.

Preferably, the pre-combustion chamber 60 comprises at least two parts, the first of these parts being the one connected to the combustion chamber 50 and the second part being the furthest away from the combustion chamber 50. The lateral wall 82 of the pre-combustion chamber 60 in the first part is closer to the rear end of the tool, than is the side wall of the pre-combustion chamber in the second part. Preferably, the second portion comprises the spark plug 65. The tool is configured such that the tool is clamped around the precombustion chamber.

Preferably, at least one diameter, and preferably both diameters of the first and second portions are constant. For example, as shown on the figure 7 , the elongate chamber of constant cross section is replaced by two portions, one upper, has a larger cross section S2 than S1 of the other, lower. The chamber 60 thus has a generally L-shaped longitudinal section. Consequently, while keeping the volume V1 constant, this embodiment has a length less than the length B of the prior art. As a result, the size of the tool can be reduced.

As we see on the figure 7 , an exemplary embodiment of the invention, the pre-combustion chamber 60 is no longer rectilinear, but includes a curvature to move the handle of the tool (which contains the pre-combustion chamber) closer to the center of gravity of the 'tool. In the example shown, a horizontal part is present. The side wall 83 (left) of the pre-combustion chamber in the portion with the spark plug is positioned closer to the side wall (right) 84 of the portion connected to the combustion chamber.

While keeping constant V1 with respect to the prior art, the invention makes it possible to keep a level of performance comparable, or even identical, in terms of energy production, in a tool that is much better balanced.

Combustion chamber

As shown on the figure 5 , the combustion chamber 50 of a tool is generally adjacent to the working chamber 80 in which the piston 78 is moved under the effect of the combustion of the air-fuel mixture.

Therefore, since the housing of the working chamber 80 is always cylindrical in shape and the piston 78 is also cylindrical in shape, the combustion chamber 50 has a generally cylindrical shape on the side of the working chamber 80.

As we see on the figure 5 this combustion chamber 50 has the shape of a flat cylinder having a diameter D and a height H, and its cavity 70 has a volume V2.

It can be seen that this chamber 50 does not lead to an optimum output of energy. They found an improved form for the combustion chamber that improves energy production.

An example of a preferred embodiment is presented at figure 8 wherein the combustion chamber defines a spherical or ovoid combustion cavity.

This spherical / ovoid shape leads to better mixing, and proper fuel distribution and flue gas scavenging. It has been discovered that this form does not have dead zones because of the presence of edges in the cavity. These edges affect both the flow and the combustion flame. The flow tends to stop as the edges approach, resulting in dead zones. The flame is also affected by these edges because it tends to go out when approaching the edges. The new form removes most, if not all, of the damaging dead spots that exist in the prior art. Even if the combustion volume is not a perfect sphere, any edge that can be removed from the volume of the combustion chamber optimizes the inlet and outlet flows of the chamber for optimal feeding with the air-fuel mixture and the optimal flushing of the combustion gases.

In addition, the mixture can burn much more efficiently in any area of the combustion chamber, minimizing dead zones. As the main reason for this improvement is the elimination of edges and blind spots, a partially spherical shape can also be replaced by a partially ovoid shape or any other shape that does not have or has a minimal number of edges, for example a where the radius of curvature of the upper part of the bottom wall (here on the left) of the combustion chamber 50 is greater than or equal to 25%, preferably 50% to the smallest diameter of the combustion chamber of the technique previous (for example, H).

The Figures 9a to 9c show a more concrete example of realization of a combustion chamber.

The combustion chamber 50 comprises a casing 68 defining three openings, two of which 50a, 50b are aligned on the same axis U, which corresponds to the longitudinal axis of the pre-combustion chamber or part thereof, and a third 50c is aligned on a Y axis substantially perpendicular to the axis U.

The casing 68 comprises a first half-shell 68a having a first wall 68aa in sphere portion. This first wall 68aa is a median wall which is located between two end walls 68ab each in cylinder portion. The end walls 68ab partially define the openings 50a, 50b of axis U. The casing 68 comprises a second half-shell 68b having two end walls 68bb each in cylinder portion and defining the rest of the axis openings. U, and a cylindrical wall 68ba defining the Y axis opening.

The opening 50a provides fluid communication with the cavity of the pre-combustion chamber. The opening 50c provides fluid communication with the internal cavity of the working chamber, and the opening 50b provides fluid communication with the atmosphere. The opening 50a can be closed by the said valve 66 and the opening 50b can be closed by a valve 84 whose moving body is carried by a rod which also carries the valve 66.

Working room

The performance of a combustion-powered fastener tool is based in particular on the ability of the piston to effectively convert the pressure energy generated by the combustion of the explosive mixture into kinetic energy transferred to the fastener. This efficient conversion is affected by leaks that occur between the piston and the housing of the working chamber. These pistons and housings are very well known because they are used in all tools. The combustion chamber design and combustion technology may vary from tool to tool, but the reciprocating piston in the crankcase will remain essentially the same for the different fasteners.

This is well known to those skilled in the art, as explained in the document EP-B1-123 717 . The combustion occurs and the pressure generated moves the piston to drive a fastener into a support material. Shortly before the piston reaches the bottom or the end of its driving stroke where it abuts on a resilient damper, the piston passes to the right of orifices in the wall of the housing, which serve for the evacuation of the combustion gases. These orifices facilitate the elimination of the combustion gases to facilitate the establishment of a partial vacuum so that air at atmospheric pressure can penetrate the piston, and facilitates the return of the latter in its position of rest or higher.

The piston used in such a tool conventionally comprises dynamic sealing means, that is to say means used to ensure a seal between the piston and the housing of the working chamber during the displacement stroke of the piston. This stroke results from a pressure difference between the two sides of the piston (combustion for driving and vacuum for return). The seals according to the prior art are configured to provide a dynamic seal.

The presence of a pre-combustion chamber increases the efficiency of combustion and the pressure inside the tool.

In its initial retracted position, the piston must first be kept sealed to contain the pressure generated by the combustion of the air-fuel mixture. As mentioned above, whenever the mixture is supercharged, or when the combustion technology uses a pre-combustion chamber, the resulting pre-pressure generated by the pre-combustion chamber, prior to ignition of the combustion chamber, must remain tight and maintain the combustion chamber without leakage. During this preliminary phase, the piston must therefore be watertight as much as possible. Ideally, the piston should also remain stable to keep the volume of the firebox low to maximize pressure until combustion is almost complete. Ideally also, in this preliminary phase, the piston should be maintained until a peak pressure occurs and combustion ends. This requirement to maintain the piston at a preliminary stage has been addressed in the prior art by using magnets or mechanisms, in particular balls, springs and / or cams. All of these piston retention mechanisms are generally bulky, complex and expensive.

Therefore, in this preliminary phase, the requirement is to ensure maximum sealing between the piston and the housing of the working chamber and therefore to have a maximum static seal when the piston is in the rest position.

Ideally, the piston should be held in this position, in a sealed manner, until the pressure peak is reached to maximize the transfer of energy in the form of combustion pressure to the driving kinetic energy of the fuel. piston.

Release of the piston is the second step of the operation, as the piston accelerates along its stroke until it reaches its opposite working position and drives the fastener into the support material. During this second step, the sealing requirement between the piston and the housing is less problematic. The dynamic sealing means are strongly stressed by the acceleration of the piston and their friction with the housing, but can meet the need satisfactorily.

There is therefore a compromise on the sealing means between the first phase requiring static sealing performance, and the second phase requiring dynamic sealing performance.

Those skilled in the art generally consider that static seals are generally flexible seals (O-rings, etc.) made of flexible materials such as rubber, silicone, etc. These are effective when there is no relative movement between the parts or if the movements are limited and slow. The same skilled person knows that dynamic seals are more capable of sealing between two moving parts, even though the seal as such is not as good as with a gasket.

For internal combustion engines, dynamic piston seals can be metal segments such as steel, which operate efficiently at high speeds and at high temperatures. other Dynamic seals also exist, such as lip seals, or composite seals, for example, although they are generally not as efficient as steel rings because of the high temperatures in the combustion engines.

This confirms the compromise mentioned above between static sealing required at the first phase of tool operation, and dynamic sealing required at the second phase. This compromise is further justified by the particular structure of the fastening tools which have one or more exhaust ports located inside the casing of the working chamber, between the two extreme positions of the piston stroke. These exhaust ports are required to evacuate the flue gases. Unfortunately, when the piston passes right of these exhaust ports, the dynamic sealing means are highly compressed and tend to expand in the open exhaust port. This situation is relatively well supported by steel joints, but not by flexible seals. Flexible seals therefore tend to wear out quickly if they are exposed to repeated passages at the exhaust ports as they tend to extrude into the exhaust ports.

It has been sought to ensure a better seal between the piston and its housing, when the piston is in its rest position, this sealing is not impaired due to the passage of the piston at the exhaust ports. Ideally, these improved sealing means should maintain the piston in its rest position until the pressure of the combustion gases in the chamber reaches a certain threshold.

The working chamber comprises a cylindrical housing for example, a piston and a first seal to seal the piston in the retracted position or rest position of the piston (static seal), and a second seal - which is different the first seal - to seal the piston during its movement (dynamic seal).

By using two different seals, each seal can be optimally matched to the required sealing function and no compromise has to be found between dynamic and static sealing.

Preferably, the second seal is attached to the piston (for example, housed in a groove of the piston). Preferably, the first seal and the second seal are both attached to the piston and the housing has a sealing surface for the first seal which is radially inside the sealing surface for sealing. the second seal. For example, the casing thus has a radial projection inwardly of the inner cylindrical surface opposite to the first seal before / during the rest position. More preferably, the first seal is attached to the housing (eg, housed within a groove of the housing). Preferably, in this case, no radially inward protrusion which holds the seal or serves as a radial sealing surface (for example in the form of a cylindrical lateral surface) is present.

While attempting to solve the problems and trade-offs listed above, several examples have been realized which are illustrated in Figures 10a to 10e .

All the exemplary embodiments show a working chamber 80 comprising a housing 90 inside which is slidably mounted a piston 78, the internal cavity 92 of the working chamber communicating with the internal cavity of a combustion chamber such as that described in the foregoing.

The piston 78 is shown in its retracted or rest position, as is known in the art and has already been explained above, and moves (downward from the orientation of the figures) in the housing 90 to drive a fastener. During its stroke, the piston may eventually pass to the right of an exhaust port 94.

The figure 10a refers to an exemplary embodimentThe piston 78 comprises a static seal 96 used to seal the piston in the preliminary phase of the actuation of the tool. In this embodiment, the gasket 96 is carried by the piston and housed in a groove of the piston. The piston also comprises a dynamic seal 98 housed in a groove of the piston.

Each joint provides its performance especially as described above. The piston is designed so that the sealing surfaces for the seals are different. In this example, the diameter of the sealing surface of the static seal 96 is smaller than the diameter of the sealing surface of the dynamic seal 98. As the piston moves downward, the dynamic seal remains in position. contact with its sealing surface throughout the race. As the dynamic seal is able to withstand repeated passages at the exhaust port 94, there is no resistance problem for this seal. At the same time, while the piston is moving (down) along its stroke, the seal 96 seals at the beginning of the race, until it emerges from its surface more small diameter sealing provided in the housing 90. Therefore, while the piston continues its course, the gasket is no longer in contact with its surface or with any other surface of the housing.

In particular, thanks to this design, the gasket 96 is never in contact with the exhaust port 94 and therefore not very stressed by friction. The gasket therefore ensures a seal that during the first phase of the operation. This situation makes it possible to use the static seal as effectively as possible without requiring compromise because it is not exposed to dynamic stresses.

The gasket may be made of flexible material, such as rubber, because it will never be in contact with the exhaust port 94 and therefore will not suffer damage by friction. In addition, the static seal can be adjusted tight so that the seal is optimized. The other advantage of this tight fit is that the gasket participates in maintaining the piston in its rest position. So, the seal Static sealing also acts as a piston retaining mechanism according to the needs of optimal combustion performance.

Referring now to the figure 10b , the general advantages described above remain applicable with the only difference that the groove provided to maintain the gasket 96 is located on the surface of the housing to be sealed. The Figures 10a and 10b represent two solutions to achieve the same effects of sealing and retention of the piston.

The figure 10c is another example of embodiment. It represents a simplification of the structure. The gasket 96 is held in place in a groove in the housing of the tool, not in the piston. There is no need for the sealing surfaces of the seals to be different. As the gasket does not follow the piston along its stroke, the gasket will not meet the exhaust port, even if the sealing surfaces are the same. In other words, the diameter of the surface of the static and dynamic seals can be identical, and the piston 78 can be designed with a single diameter. Therefore, this simplified exemplary embodiment also provides all the advantages in terms of static sealing, dynamic sealing and retention of the piston in its rest position.

The Figures 10d and 10e are other examples of embodiment. They are actually another design examples of realizations of Figures 10a and 10b . The piston uses two different sealing surfaces for static sealing and dynamic sealing. The difference being that in the Figures 10a and 10b , the piston is the male part of the sealing surface of the static seal, while in the Figures 10d and 10e , the piston is the female part of the sealing surface of the static seal. Here again, the advantages of the invention are the static sealing, the dynamic sealing and the retention of the piston in its rest position.

In the various exemplary embodiments, the piston 78 has an elongated shape and comprises a coaxial head and a rod. The seal static 96 is located in an area of the piston head, near a longitudinal end thereof, which is opposite the rod.

Claims (10)

1. Combustion or precombustion chambers (60) for a gas-powered fixing tool (10), comprising a casing (62,68) defining a first combustion cavity (64) having a generally elongate form of longitudinal axis X, and a second combustion cavity (70), ignition means, such as a spark plug (65), being situated at a longitudinal end of said cavity and a longitudinal end of said first cavity, which is opposite said ignition means, being fluidically connected with said second cavity, characterized in that said first cavity has a variable cross section along said axis X, said first cavity having a generally staged form and comprising at least one first portion of cross section S1 and one second portion of cross section S2, with S1 smaller than S2, said ignition means being situated in said first portion.
2. Chambers (60) according to the preceding claim, in which said first cavity has, in longitudinal section, a generally L or T-shaped form.
3. Chambers according to one of the preceding claims, in which said second cavity has at least partly a spherical or ovoid form.
4. Chambers (50) according to the preceding claim, in which said casing defines three openings (50a, 50b, 50c), two of which are aligned on a same axis U and a third of which is aligned on an axis Y substantially at right angles to the axis U.
5. Chambers (50) according to Claim 3 or 4, in which said casing comprises a first half-shell (68a) comprising a first wall (68aa) in the form of a portion of sphere.
6. Chambers (60) according to the preceding claim, in which said first wall (68a) is a median wall (68aa) which is situated between two end walls (68ab) each in the form of a portion of cylinder.
7. Chambers (60) according to Claims 5 and 6, dependent on Claim 4, in which said end walls (68ab) partly define said openings of axis U.
8. Chambers (60) according to the preceding claim, in which said casing comprises a second half-shell (68b) comprising two end walls (68bb) each in the form of a portion of cylinder and partly defining said openings of axis U, and a cylindrical wall (68ba) defining said opening of axis Y.
9. Chambers according to one of the preceding claims, in which they comprise a casing (90) defining a housing in which a piston (78) is mounted and can slide to drive a fixing element, said piston being configured to be translationally displaced in said housing from a rest position to a working position, said housing being fluidically connected with said second cavity.
10. Gas-powered fixing tool, comprising chambers (50, 60) according to one of the preceding claims.

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