Tool driving or impacting – Processes
Reexamination Certificate
2002-04-30
2004-01-06
Smith, Scott A. (Department: 3721)
Tool driving or impacting
Processes
C173S115000, C173S206000, C173S207000
Reexamination Certificate
active
06672403
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application claims the priority of German Patent Application No. 101 23 202.0 filed May 12, 2001, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The invention relates to a method for protecting a fluid-operated percussion device against no-load strokes, having a percussion piston that moves inside a work cylinder and impacts a tool, the piston having two piston surfaces of different sizes, of which the smaller surface, being active in the direction of the return stroke, is permanently connected to a pressure line that is subjected to the working pressure, while the larger piston surface, being active in the direction of the work stroke, is alternately connected via a control valve to the pressure line and a pressure-relieved return line; a control unit that includes a distributing regulator, which moves inside the control valve and has two regulator surfaces that differ in size and are active in opposite directions of movement, with the smaller of the surfaces, which acts on the distributing regulator in the direction of the return-stroke position of the regulator, being permanently connected to the pressure line, and the larger regulator surface being connected only alternately and temporarily to the pressure line and the return line via a circumferential groove disposed between the piston surfaces; a no-load-stroke port that opens into the interior of the work cylinder, with the port first being opened toward the interior by the front piston collar of the percussion piston with the smaller piston surface after the percussion piston has overshot the normal impact position by an established distance in the work-stroke direction until it has assumed a no-load-stroke position; and a safety element, which is disposed upstream of the no-load-stroke port, and can be switched between two end positions—the inoperative position and the active position—and is connected on the intake side to the pressure line and serves in exerting the working pressure that originates from the safety element onto the no-load-stroke port in the active position, or, in the inoperative position, serves in breaking the connection between the pressure line and the no-load-stroke port, in which instance the working pressure exerted on the no-load-stroke port in the active position blocks the distributing regulator in the work-stroke position by way of the circumferential groove, should the percussion piston attain the no-load-stroke position.
The invention further relates to an apparatus that is suited for executing the method.
Depending on the working and application conditions, it may be desirable to equip fluid-operated percussion devices with a mechanism that protects against no-load strokes, particularly in the interest of avoiding an undesired stress or resulting damage. The Japanese published, non-examined patent application Hei-10-80878 of Mar. 31, 1998, proposes a solution relating to a hydraulic percussion device.
German Patent Application 100 13 270.7 of Mar. 17, 2000, proposes to equip a fluid-operated percussion device of the generic type mentioned at the outset with a manually-operated no-load-stroke protection mechanism in the form of a switchable safety element such that the percussion piston is shut down—independently of other control-related circumstances—should it reach a defined extended position in the direction of the work stroke.
SUMMARY OF THE INVENTION
It is the object of the invention to build upon the solution presented in the cited German patent application by providing a method and an apparatus that permit the no-load-stroke protection mechanism to be activated automatically, regardless of the manipulation of the device by an operator. The method and the apparatus are intended to be embodied such that the percussion device will not be shut down upon startup when it is subjected to the working pressure, but always can at least start up.
The object is accomplished according to a first aspect of the invention by a method of protecting a fluid-generated percussion devices of the type originally defined wherein the safety element is transferred from its inoperative position into its active position some time after the startup of the percussion device subjected to the working pressure—counter to the effect of a resetting mechanism that acts on the safety element. As a consequence of the operating mode of the percussion device, a larger activation force that counteracts the resetting action is generated continuously, or at least temporarily at recurring time intervals. This ensures that the safety element is always switched to be active due to the effect of the activation force after the percussion device has started up, in case the percussion piston moves in the work-stroke direction and may be able to reach the no-load-stroke position. As already mentioned, the subject of the invention can be embodied such that the safety element is either held continuously in the active position it has assumed once after the startup of the percussion device, or it is transferred again into its active position, at least in repeating intervals.
According to features of the invention, the method can be executed such that the safety element is transferred into its active position over the course of the first work cycle of the percussion piston or over the course of the first return-stroke movement of the percussion piston after the percussion device has started up. The work cycle encompasses the work-stroke and return-stroke movements, or the return-stroke and work-stroke movements, of the percussion piston. According to a teaching of the invention, the activation force acting on the safety element can be generated by the working pressure building up temporarily in a percussion-device line that is periodically subjected to pressure during the operation of the percussion device. Furthermore, the method can be embodied such that the safety element is temporarily transferred into its active position within the time frame, and maintained in this position while the percussion-device line is subjected to the working pressure.
The activation force acting on the safety element can be built up by the working pressure present in the no-load-stroke port. The safety element can, however, also be transferred into its active position if the larger piston surface of the percussion piston or the larger regulator surface of the distributing regulator is subjected to the working pressure for the first time after the percussion device has started up.
The method can also be embodied such that the safety element is gradually transferred into its active position, as a function of the operating period, after the percussion device has started up. For this to happen, a delay element can cause the safety element to execute a partial switching stroke per time unit in the direction of its active position, with the partial switching stroke being smaller than the switching stroke with which the safety element is transferred out of the inoperative position into the active position.
As an alternative, the control surface of the safety element can be supplied with a limited control volume, as a function of pressure fluctuations occurring periodically during the operation of the percussion device; consequently, the safety element is transferred in increments into the active position.
In a particularly simple embodiment of the subject of the invention, the limited control volume can be created by a percussion-device line equipped with a throttle element, which is periodically subjected to the working pressure during the operation of the percussion device. In this regard, the following lines in particular are considered as a percussion-device line: the alternating-pressure line, by way of which the larger piston surface of the percussion piston is temporarily exposed to the working pressure; the reversing line, by way of which the control valve of the percussion device can be switched into the work-stroke position; the short-stroke line, in the event that the percussion de
Ahr Torsten
Deimel Thomas
Lohmann Stefan
Burdett James R.
Krupp Berco Bautechnik GmbH
Kunitz Norman N.
Venable LLP
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