Internal-combustion engines – Free piston – Single chamber; one piston
Reexamination Certificate
2001-07-03
2003-03-18
Mancene, Gene (Department: 3747)
Internal-combustion engines
Free piston
Single chamber; one piston
C123S0460SC
Reexamination Certificate
active
06532917
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a portable, internal combustion engined power tool, in particular a setting tool for driving in fastening elements, and including a combustion chamber, at least one suction/discharge valve connected wit the combustion chamber, and an operational piston which performs an operational stroke upon ignition of a fuel gas mixture filling the combustion chamber. The present invention also relates to a method of controlling operation of such a power tool.
2. Description of the Prior Act
With a power tool of a type described above, the drive energy is generated by burning a fuel gas mixture in a combustion chamber and is transmitted by the operational piston to a fastening element. Upon pressing a power tool against a constructional component into which a fastening element is to be driven, an ignitable fuel gas mixture is injected into the combustion chamber. Upon actuation of a trigger, a spark is produced which ignites the fuel gas mixture, initiating a combustion process. The operational piston, which adjoins the combustion chamber, is driven by the combustion gases. At the end of its operational stroke, the piston passes past discharge openings through which the waste gases can be at least partially discharged. The piston, after having performed the operational strokes, returns in its initial position as a result of underpressure which was created in the combustion chamber by cooling of the waste or residual gases. During the period of thermal return of the piston to its initial position, the combustion chamber should remain sealed from the surrounding it environment. Therefore, the suction/discharge valves, which provide for delivery of fresh air into the combustion chamber, should be open only after the piston has returned into its initial position. Generally, the time necessary for the return of the piston into its initial position increases with the increase of the tool temperature which heats during operation. In addition, high-energy power tools require a large expansion volume which results in that a greater time becomes necessary for the return of the piston into its initial position.
In some conventional power tools, closing of a suction/discharge valve can be effected with a pawl connected by, e.g., a toggle lever with the trigger. In this way, the suction/discharge valve becomes open as soon as the trigger returns into its initial position. This means that by the time the trigger returns to its initial position, the piston also must return into its initial position.
The locking of the suction/discharge valve by the trigger means that the switching point of the trigger cannot any more be arbitrary selected. The ignition switch can only then be actuated when the locking of the suction/discharge valve has been completed, i.e., long after the start of the displacement of the trigger. However, a long trigger displacement adversely affects acceptance by the customers. Moreover, as it has already been discussed above, with a heated tool, the return of the piston into its initial position lasts longer. The tool user must, in this case, hold the trigger in its pulled condition longer to prevent the piston from occupying a erroneous position.
In order to increase the time available for return of the piston into its initial position, the trigger displacement can be damped. However, damping negatively influences operational characteristics of the trigger as a larger force is needed for actuating the trigger, and the trigger does not return sufficiently rapidly into its initial position. A user does not look at dampening favorably as it reduces the maximum setting rate and requires a greater force for actuating the trigger, which the user has to apply.
German Publication DE 19962 598.0 suggests detecting of the gas pressure in the combustion chamber after the fuel gas mixture has been ignited and locking the suction discharge valve(s) dependent on the detected gas pressure.
Accordingly, an object of the present invention is to provide a method which would permit to precisely determine when the piston returns into its initial position and thereby would provide for a more precise control of release of the suction/discharge valve.
Another object of the present invention is to provide a power tool which would contain means that would permit more precisely determine the return of the piston into its initial position.
SUMMARY OF THE INVENTION
These and other objects of the present invention, which would become apparent hereafter, are achieved by providing a method according to which the displacement position off the piston is inquired, and the suction/discharge valve is released after the return of the piston in its initial position has been ascertained.
The tool according to the present invention includes inquiry means for inquiring the piston position and which actuates a locking/release device associated with the suction/discharge valve for opening same.
According to the present invention, the method for operating a portable internal combustion engined power tool including a combustion chamber, at least one suction/discharge valve for supplying fresh air into the combustion chamber and for discharging waste gases therefrom, and an operational piston displaceable in an operational direction upon ignition of a fuel gas mixture filling the combustion chamber, includes inquiring a displacement position of the piston when it is being displaced to its initial position after having performed an operational stroke; and releasing the at least one valve upon the piston reaching its initial position.
The foregoing method permits to precisely determined the geometrical position of the piston, in particular, its initial position. The release or opening of the suction/discharge valve is effected only when the piston has reached its initial position. The pressure variations of the residual gases in the combustion chamber do not lead any more to a faulty control during the valve release. The danger of the valve being released before th piston reaches its initial position is completely eliminated. The initial position of the piston is a position in which the opening between the combustion chamber and the guide cylinder is completely closed.
In principle, for inquiring the displacement position of the piston, a position of any portion of the piston can be monitored. However, because the piston is guided in a guide cylinder and has a piston rod at least a portion of which projects from the guide cylinder, according to embodiments of the invention, it is the position of the piston rod which is being ascertained. In this case, the access to the inside of the cylinder or the combustion chamber is not any more necessary. Therefore, the inquiring element or device for determining the displacement position of the piston can be formed much simpler, and it can be mounted much easier. The displacement position of the piston can be easily ascertained from the displacement position of the piston rod. Based on the principle that it is the initial position of the piston that need be ascertained, a corresponding clearly defined point on the piston rod can be monitored, e.g., by using a stationary sensor. Passing of the defined point of the piston rod past the sensor, upon returning of the piston to its initial position, is a clear indication that the piston has reached its initial position.
According to one embodiment of the present invention, as a defined point which has to be monitored for determining the displacement position of the piston rod, the end surface of the piston rod is used. The position of the end surface of the piston rod can be monitored very easily and very precisely. This permits to precisely determine the return of the piston to its initial position.
In case, the piston rod has not returned to its initial position after the performance of the operational stroke, according to a further development of the present invention, a forceful release of the suction/discharge valve is provided for. The forceful release is
Saxler Wolfgang
Thieleke Joachim
Benton Jason
Hilti Aktiengesellschaft
Mancene Gene
Sidley Austin Brown & Wood LLP
LandOfFree
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