Elongated-member-driving apparatus – Explosive-type driving means – With plunger
Reexamination Certificate
2003-06-16
2004-06-29
Smith, Scott A. (Department: 3721)
Elongated-member-driving apparatus
Explosive-type driving means
With plunger
C227S130000, C123S0460SC
Reexamination Certificate
active
06755335
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a setting tool for driving fastening elements, such as nail, bolts, pins, etc . . . in a constructional component and includes a combustion chamber in which combustion of an air-fuel mixture takes place, a guide cylinder adjoining the combustion chamber, and a piston displaceable in the guide cylinder under pressure generated as a result of the combustion of the air-fuel mixture in the combustion chamber.
2. Description of the Prior Art
Setting tools of the type described above are operated by gaseous or liquid fuel that is evaporated before combustion. The setting energy for driving in a fastening element is produced by combustion in the tool combustion chamber of a gas-air mixture and is transmitted to the fastening element by a piston.
U.S. Pat. No. 4,365,471 discloses a setting tool in which the combustion space is divided in at least two chambers separated by a plate in which overflow openings are provided. During a setting process, the combustion of an air-gas mixture starts in a first chamber provided with an ignition device. After the ignition, the flame front expand with a comparatively low speed in the first chamber, displacing the non-combusted gas-air mixture toward the chamber wall and which flows through the overflow openings into next chamber, producing in the next chamber turbulence and precompression. As soon as the flame front reaches the overflow openings, the flame jets that flow therethrough are accelerated due to the small cross-section of the openings, creating in the next chamber a further turbulence. The intermixed, turbulent gas-air mixture in the second chamber is ignited over the entire surface of the flame jets. It burns with a high speed which provides for a high effectiveness of combustion as the losses due to cooling are very small. The scavenging of the combustion space is effected with an additional device with which the waste gas is evacuated and fresh air is fed.
German Patent DE 40 32 202 C2, from which the present invention proceeds, discloses a setting tool that operates on a principle of a divided combustion chamber according to U.S. Pat. No. 4,365,471. In the setting tool of the German Patent, however, the chambers of the combustion space are separated from each other by a displaceable intermediate or separation plate and are limited toward the rear by a displaceable cylindrical top plate. For evacuating of the waste gases from the combustion space, the cylindrical top plate and the separation plate are displaced toward the bottom of the combustion space, reducing the remaining combustion volume and expelling the waste gases out of the tool. The combustion space is filled with air upon expansion of combustion chambers when the setting tool is pressed against a constructional component.
The drawback of the foregoing setting tools consists in that the volume of the chambers or of the combustion space cannot be reduced to an absolute zero. Therefore, a complete scavenging of the combustion space does not take place with a single displacement step. Rather, in one or more chambers, a certain amount of the waste gas, which depends on the volume of remaining slots, bores, and other so-called dead volumes, remains. The remaining waste gas mixes with air when the air is aspirated and adversely affects the concentration of the mixture and thereby the amount of energy produced by combustion.
Accordingly, an object of the present invention is a setting tool of type in which the waste gas is completely expelled.
SUMMARY OF THE INVENTION
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing means for forming a scavenging chamber adapted to be filled with scavenging air and pneumatically connected with the combustion chamber, the forming means including at least one slide member for discharging the scavenging air from the scavenging chamber toward the combustion chamber.
The present invention provides a scavenging chamber that can be filled with outside air before or after the setting process and which is at least partially pneumatically connected with the combustion chamber. There is provided, according to the present invention at least one slide member that forces the air out of the scavenging chamber, through the combustion chamber, and in the atmosphere. This measures provides for scavenging of the combustion chamber and cleaning it from possibly still filling it, waste gases. The scavenging air can be introduced, e.g., already during the setting process by suitable means into the scavenging chamber, and after the setting process has been finished, the air from the scavenging chamber can be forced out with the slide member and be introduced into the combustion chamber. An additional electrical drive, e.g., for a ventilator, can be eliminated. Moreover, providing a scavenging chamber capable to be filled with scavenging air, insure a complete scavenging of the combustion chamber.
According to an advantageous embodiment of the present invention, the combustion chamber is divided in at least two chamber section by a separation plate. After completion of the setting process, the volume of the combustion chamber is reduced at least in one of the chamber sections by displacement of the separation plate in the setting direction which results in evacuation of a major portion of the residual waste gas from the combustion chamber or at least from the one of the chamber sections the volume of which is being reduced. Simultaneously, with the reduction of the volume of the combustion chamber, the scavenging chamber for receiving the scavenging air, the front, in the setting direction, end of which is limited by the separation plate and the rear end of which is limited by the slide member expands. The filling of the scavenging chamber with the air is effected through channels formed in the setting tool housing. In this embodiment, the scavenging chamber can be easily filled with outside air as a result of displacement of the separation plate which is displaced either as result of cooling of the fuel gases or by an additional spring means that applies a biasing force to the separation plate acting in the setting direction. When the scavenging chamber is filled with the outside air after the completion of the setting process, the heating of the scavenging air is substantially prevented, and the scavenging of the combustion chamber is effected with a relatively cold and dense air.
Advantageously, the slide member is axially displaceably arranged in the setting tool, and the scavenging air is forced out of the scavenging chamber as a result of displacement of the slide member in the setting direction.
A simple and place-saving construction of the setting tool is obtained when the slide member is also formed as a plate extending parallel to the separation plate.
According to a further advantageous embodiment of the present invention, the scavenging of the residual volume of the combustion chamber is effected only after the separation plate reaches its end, in the setting direction, position in which the volume of the combustion chamber is reduced to a minimum. This can be achieved, e.g., by providing in the cylindrical wall of the combustion chamber, at least one channel or a bypass that communicates the scavenging chamber with an intermediate chamber or chamber of the combustion chamber only in the end, in the setting direction, position of the separation plate.
In order to retain the slide member in its operational position during filling of the scavenging chamber with air, advantageously, a retaining mechanism is provided which releasably retains the slide member in its operational position. For an automatic displacement of the slide member in a direction in which the slide member forces the scavenging air out of the scavenging chamber, a spring is provided. Upon release of the retaining mechanism, the spring biases the slide member in a direction toward the combustion chamber, and the slide member forces the scaveng
Hilti Aktiengesellschaft
Sidley Austin Brown & Wood LLP
Smith Scott A.
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