Hydraulic hammering device

A hydraulic hammering device, comprising:

• a cylinder;
• a piston slidably fitted into the cylinder in such a manner as to be capable of advancing and retracting;
• a first control valve to control advancing and retracting movements of the piston;
• an auto-stroke mode configured to switch a piston stroke of the piston between a regular stroke and a short stroke shorter than the regular stroke;
• an idle strike prevention mode configured to decompress an inside of a circuit configured to hydraulically drive the piston to lower than a working pressure;
• and
• a second control valve to select either mode of the auto-stroke mode and the idle strike prevention mode, wherein the second control valve has a high pressure port connected to a high pressure passage, a decompression port connected and cut off from a decompression passage, and a cylinder communication port connected and cut off from a stroke control passage, and wherein:
• to the second control valve, a shared spool including an auto-stroke setting portion and an idle strike prevention setting portion at a same time is slidably fitted,
• a mode selection means comprising:
• a second switching valve configured to move so that pressurized oil is cut off and supplied to the auto-stroke setting portion and a first switching valve configured to move so that pressurized oil is discharged from the idle strike prevention setting portion is disposed, and
• the mode selection means is configured in such a way that:
• when the first switching valve and the second switching valve are in a regular position, the auto-stroke mode is selected by the second switching valve allowing pressurized oil to be supplied to the cylinder communication port constituting the auto-stroke setting portion, and by the first switching valve prohibiting pressurized oil from being discharged from the decompression port constituting the idle strike prevention setting portion, and
• when the first switching valve and the second switching valve are in an upper position, the idle strike prevention mode is selected by the second switching valve prohibiting pressurized oil from being supplied to the cylinder communication port constituting the auto-stroke setting portion, and by the first switching valve allowing pressurized oil to be discharged from the decompression port constituting the idle strike prevention setting portion.