This invention relates to an internal combustion engine fastening device, wherein a piston is mounted in a cylinder for being propelled forwards therein and driving, in turn, a fastening member into a support material, under the action, in a combustion chamber, of an air and fuel mixture being ignited.

Generally, in devices of such a type, at rest, the driving piston is located in a high position, at the base of the combustion chamber closing under the abutment of the device against the support material. The mixture being ignited is at the atmospheric pressure.

It has already been suggested, for obtaining more power, generating a pressure peak, to pre- compress the mixture in the chamber before the ignition .

Thus, FR 2,840,555 teaches a device wherein the pre-compression occurs forward of the piston in the cylinder being then used as a primary combustion chamber .

Such a solution however requires quite heavy means for maintaining the piston in a high position, igniting in the primary chamber and communicating between the primary chamber-cylinder and the actual combustion chamber for propelling the piston forwards.

The invention of the present application provides a fastening device through pre-compression of the gas contained within the combustion chamber of the above defined type, characterized in that, the piston moving down forward of the cylinder, it comprises means for moving it up backward of the cylinder, at the base of the combustion chamber.

Thus, thanks to this invention, after the chamber is closed through the abutment of the device, the upward movement of the piston compresses the gas enclosed within the combustion chamber and the cylinder, until the piston reaches its high position, before the air and fuel mixture within the chamber, at a higher pressure than the atmospheric pressure, is ignited .

It should be noticed that the down position of the piston, forward of the cylinder, will be generally reached when the device is at rest, but not necessarily. Moreover, the position referred to as forward of the cylinder does not necessarily involve that this is the extreme advanced position. The piston could also be only moved down partially forward of the cylinder, without, nevertheless, reaching such an extreme advanced position.

As means for moving the piston up backwards, an assembly could be considered comprising an electric engine and a cam, a rack, a roller, and a motor reducer-piston unit.

This invention also relates to a method for fastening a fastening member by means of a fastening device acting through pre-compression of the gas contained within the combustion chamber of the above defined type, characterized in that, the piston being moved down forward of the cylinder, the gas contained within the cylinder and the combustion chamber is compressed moving the piston up backward of the cylinder and at the base of the chamber, the air and fuel mixture being formed by fuel injection at any time upon the piston moving up, before or after.

The fuel could be injected at any time, the essential point being that the mixture should be ignited being at a pressure higher than the atmospheric pressure.

This invention will be better understood reading the following description of a preferred embodiment of the device of this invention, referring to the very schematic appended drawing, wherein:

- Fig. 1 shows the device at rest, the piston being moved down forward of the cylinder;

- Fig. 2 shows the device of Fig. 1 upon sweeping by the fan of the combustion chamber;

- Fig. 3 shows the device engaged on a support material and the combustion chamber being closed;

- Fig. 4 shows the device, the piston being moved up backward of the cylinder and the gas being pre-compressed;

- Fig. 5 shows the device, after the explosion, the piston being propelled forwards and driving a nail into the support material;

- Fig. 6 shows the device at the end of the piston stroke after opening of the exhaust holes, and

- Fig. 7 shows the device, still in abutment, but reopened with fresh and cooling air recirculation for the following shot.

The fastening device that is now going to be described is here a nailing device. But it could also be a device of the same type, that is to say comprising an internal combustion engine, but being able to drive other fastening members, such as, for example, staples.

The device thus comprises a combustion chamber 1, wherein an air and fuel mixture is to be ignited and exploded for propelling forwards a piston 2 for driving a nail 3 (Fig. 5) into a support material 4. Backward of the chamber, a cylinder head 5 is arranged carrying a mixture igniting member, in the present case a sparkling plug 6, and a motor fan 7, for blending the mixture and circulating the air.

Forward of the combustion chamber 1 a cylinder 8 extends wherein the piston 2 is mounted.

The cylinder front is perforated with exhaust holes 9 and forward of such holes, in the bottom of the cylinder, a damping device 10 is arranged for the piston being at the stroke end.

The driving piston 2 comprises a head 11 and a driving rod 12.

Forward of the cylinder 8, a tip-guide 16 extends, for receiving a fastening nail from a magazine as well as the rod 12 of the piston 2.

All the members of the device that have just been described are perfectly known to those skilled in the art .

The device is provided with means 13 for mechanically driving the piston 2.

In the example being considered, this is a rack mechanism comprising a front portion 14 of the rod of the piston 12 provided with teeth onto which a driving pinion 15 can be geared, said pinion being rotatably mounted on the tip-guide 16 of the device. The rotation of the pinion of the rack occurs via a small engine. The rack mechanism 13 is here a double action mechanism in that it both enables moving the piston 2 up in the cylinder 8 as well as moving it down, although this latter function is perfectly secondary and will be hereinafter referred to.

Having described the members of the device, the operation thereof will be now described, that is, the fastening method that can be implemented by means of such a device.

The device being at rest, the combustion chamber 1 is opened backward, the piston 2 moved down in the low position forward of the cylinder 8, the head of the piston 11 being located in abutment against the damping device 10. While actuating the motor fan 7, some air is being circulated, being entered from the rear of the chamber, through the thus swept chamber 1 and cylinder 8; the air comes out through the exhaust holes 9.

Such a sweeping is illustrated by the air stream arrows 17 (Fig. 2) .

The device is put into abutment against the support material 4 intended to receive a nail. As a result of the tip-guide 16 sliding backwards, conventionally, the cylinder head 5 covers and closes the chamber 1 at the rear (Fig. 3) . Thus, some fresh air is enclosed within the space inside the chamber 1 and the cylinder 8.

The rack 13 is actuated for moving up the piston 2 and sliding the head 11 thereof in the cylinder 8 until it reaches the rear of the cylinder and the base of the chamber, thereby closing the chamber 1 forward (Fig. 4) . The gas that was spread in the chamber 1 and the cylinder 8 is then compressed and enclosed within the single chamber 1 (Fig. 4) . This is the pre-compression of the gas.

In order to form the air and fuel mixture, the fuel has been injected into the combustion chamber 1 while the piston 2 is moving up, in a perfectly conventional way. It should be noticed that it could have been injected before or even after such moving up, the essential point being that the air and fuel mixture, in the condition of the device of Fig. 4, with the chamber closed, is at a higher pressure than the atmospheric pressure.

The man of the art perfectly knows how he can set up into the fastening device that has just been described, all means enabling fuel injection into the chamber, from the source of fuel - a cartridge - up to the injection ducts via a solenoid type injection device or another piezoelectric injector.

The ignition of the sparking plug 6 is then controlled, resulting in the mixture exploding and the head of the piston 11 being propelled in the cylinder 8, until it comes in abutment against the damping device 10 (Fig. 7) . While the piston is moving down, the pinion of the rack has remained released. Via its rod 12, the piston drives into the support material 4 the nail 3 that has been introduced into the tip-guide 16 from the supply magazine (Fig. 5) .

It could be contemplated, despite the difficulty of manufacture, controlling the rack so that it also drives the piston in its descent stroke simultaneously while the mixture is being exploded, so as to increase the strength applied to the piston. A little before the end of its descent stroke (Fig. 6), the head of the piston 12 has reached the area of the thus released exhaust holes 9 for the exhaust of the burnt gases (arrows 18) .

After the piston 2 has driven the nail 3 into the support material 4, the device is driven out of abutment (Fig. 7), resulting in the rear opening of the chamber 1 and thereby in some fresh air arriving and an air stream 19 coming from the rear of the chamber 1 until the exhaust holes 9, so as to cool down the chamber 1 and the cylinder 8 and to recycle fresh air for the next shot.

It should be noticed that the rack could be controlled so as to maintain the piston in a low position at rest.

It has been described, as mechanical driving means of the piston, a rack mechanism. A kinetic assembly could also be implemented with a rotary lift of the type as described in WO 2009/046076 Al .