Damped hammer drill

A hydraulic hammer drill usable in combination with a hydraulic pressure source having a high-pressure side and a low-pressure side and with a tool having a shaft with a rear end, the hammer comprising:

• a housing formed with an axis-defining bore having a front end in which the tool shaft is normally coaxially engaged;
• a piston coaxially displaceable in the bore, having a forwardly directed face defining in the bore a front return chamber of small effective piston surface area, and having a rearwardly directed face defining in the bore a rear drive chamber of larger effective surface area;
• a passage permanently connecting the front chamber with the high-pressure side of the hydraulic pressure source;
• means including a reversible control valve connected between both sides of the hydraulic pressure source and the rear chamber for alternately pressurizing and depressurizing the rear chamber and thereby alternately displacing the piston axially forward to a front position in which it strikes the rear end of the tool shaft and axially backward away from the tool;
• at least one recoil-damping sleeve surrounding the piston axially ahead of the front chamber and having a front end axially forwardly operatively engageable with the tool shaft in a frontmost position and a rear end defining with the bore a recoil chamber separated from the front return chamber, the housing being formed with a vent passage connected to the low-pressure side of the hydraulic pressure source and opening into the recoil chamber, the vent passage being uncovered by the sleeve for venting of the recoil chamber substantially only when the sleeve is in the frontmost position, the piston being formed with
• at least one bypass passage communicating for fluid flow between the recoil and front chambers when the piston is in or axially forward of its front position but blocked when the piston is axially backward of its front position and with
• another such bypass passage axially rearward of the first-mentioned bypass passage, whereby when there is no tool in the hammer drill the piston moves forward past its front position and the front chamber is vented to the low-pressure side of the source through the other bypass passage.

A hydraulic hammer drill usable in combination with a hydraulic pressure source having a high-pressure side and a low-pressure side and with a tool having a shaft with a rear end, the hammer comprising:

• a housing formed with an axis-defining bore having a front end in which the tool shaft is normally coaxially engaged;
• a piston coaxially displaceable in the bore, having a forwardly directed face defining in the bore a front return chamber of small effective piston surface area, and having a rearwardly directed face defining in the bore a rear drive chamber of larger effective surface area;
• a passage permanently connecting the front chamber with the high-pressure side of the hydraulic pressure source;
• means including a reversible control valve connected between both sides of the hydraulic pressure source and the rear chamber for alternately pressurizing and depressurizing the rear chamber and thereby alternately displacing the piston axially forward to a front position in which it strikes the rear end of the tool shaft and axially backward away from the tool;
• at least one recoil-damping sleeve surrounding the piston axially ahead of the front chamber and having a front end axially forwardly operatively engageable with the tool shaft in a frontmost position and a rear end defining with the bore a recoil chamber separated from the front return chamber, the housing being formed with a vent passage connected to the low-pressure side of the hydraulic pressure source and opening into the recoil chamber, the vent passage being uncovered by the sleeve for venting of the recoil chamber substantially only when the sleeve is in the frontmost position, the piston being formed with at least one bypass passage communicating for fluid flow between the recoil and front chambers when the piston is in or axially forward of its front position but blocked when the piston is axially backward of its front position, the sleeve being formed with an internal passage that opens into the vent passage and into the recoil chamber in the frontmost position of the sleeve.

A hydraulic hammer drill usable in combination with a hydraulic pressure source having a high-pressure side and a low-pressure side and with a tool having a shaft with a rear end, the hammer comprising:

• a housing formed with an axis-defining bore having a front end in which the tool shaft is normally coaxially engaged;
• a piston coaxially displaceable in the bore, having a forwardly directed face defining in the bore a front return chamber of small effective piston surface area, and having a rearwardly directed face defining in the bore a rear drive chamber of larger effective surface area;
• a passage permanently connecting the front chamber with the high-pressure side of the hydraulic pressure source;
• means including a reversible control valve connected between both sides of the hydraulic pressure source and the rear chamber for alternately pressurizing and depressurizing the rear chamber and thereby alternately displacing the piston axially forward to a front position in which it strikes the rear end of the tool shaft and axially backward away from the tool;
• at least one recoil-damping sleeve surrounding the piston axially ahead of the front chamber and having a front end axially forwardly operatively engageable with the tool shaft in a frontmost position and a rear end defining with the bore a recoil chamber separated from the front return chamber, the housing being formed with a vent passage connected to the low-pressure side of the hydraulic pressure source and opening into the recoil chamber, the vent passage being uncovered by the sleeve for venting of the recoil chamber substantially only when the sleeve is in the frontmost position, the piston being formed with at least one bypass passage communicating for fluid flow between the recoil and front chambers when the piston is in or axially forward of its front position but blocked when the piston is axially backward of its front position, the bypass passage being formed by a plurality of axial outwardly open grooves.