Method and apparatus for protecting a fluid-operated percussion device against no-load strokes

An apparatus for executing a method for protecting a fluid-operated percussion device (1) against no-load strokes, said apparatus comprising:

• a percussion piston (3) that moves inside a work cylinder (2) and impacts a tool (4), with the piston having two opposed piston surfaces (A1, A2) of different sizes, of which the smaller surface (A1), which is oriented to be active in the direction of a return stroke, is permanently connected to a pressure line (8) that opens into the work cylinder and is subjected to the working pressure, while the larger piston surface (A2), which is oriented to be active in the direction of the work stroke (arrow 3e), is alternately connected via a control valve (5) to the pressure line and a pressure-relieved return line (10);
• a control unit that includes a distributing regulator (5a), which moves in the control valve (5) and has two regulator surfaces that differ in size and are active in opposite directions of movement, with a smaller of the two regulator surfaces (S1), which acts on the distributing regulator (5a) in the direction of a return stroke of the regulator, being permanently connected to the pressure line (8), and the larger of the two regulator surfaces (S2) being connected alternately and temporarily during movement of the piston to the pressure line or the return line (8 or 10) via a circumferential groove (3c) disposed on the piston between the piston surfaces (A1, A2);
• and forms front and rear piston collars;
• a no-load-stroke line having a no-load stroke port (20a) that opens into the interior (2d) of the work cylinder (2), with the port being located in the longitudinal direction of the work cylinder such that it is first opened toward the interior of the work cylinder (2d) by the front piston collar (3b) of the percussion piston (3) which has the smaller piston surface (A1), after the percussion piston (3) has overshot the normal impact position by an established distance in the direction of the work-stroke direction (arrow 3e) until it has assumed a no-load-stroke position;
• and
• a safety element (21;
• 33 or 46), which is disposed in the no-load stroke line upstream of the no-load-stroke port (20a), and can be switched between end positions, including an inoperative end position and an active end position, and is connected on the intake side to the pressure line (8), with the working pressure that originates from the safety element (21;
• 33 or 46) being exerted on the no-load-stroke port (20a) via the safety element when in the active end position, and breaking the connection between the pressure line (8) and the no-load-stroke port (20a), when in the inoperative end position, wherein the working pressure present at the no-load-port (20a) in the active position, blocks the distributing regulator (5a) in the work-stroke position via the circumferential groove (3c), should the percussion piston (3) have attained the no-load-stroke position;
• the safety element (21;
• 33 or 46) is formed by an automatically-controlled two-position valve that is provided with a resetting mechanism (23) and has a control surface (21a;
• 33a or 46a) that influences its position, and can be subjected, via a signal line, to a pressure level that forms a control signal such that the two-position valve is first transferred out of its inoperative position and into its active position some time after the percussion device (1) has started up, and counter to the effect of the resetting mechanism (23);
• and
• the two-position valve (21;
• 33 or 46) is configured such that it maintains its active position, as effected under the influence of the control signal, at least temporarily in repeating intervals.