| 摘要 |
1,220,941. Drilling machines. TOLERANS A.B. 14 Feb., 1968 [15 Feb., 1967], No. 7212/68. Heading B3C. [Also in Division B4] A percussive tool comprises a drive piston reciprocable within a cylinder to pressurize liquid in the cylinder and thereby effect reciprocation of a hammer piston part of which extends into the cylinder, and a valve sleeve engageable by the drive piston when the latter is moved towards the hammer piston until the drive piston reaches a predetermined position at which position the valve sleeve is urged away from the drive piston to open return passageways within the drive piston to allow the liquid to pass from the cylinder to a chamber outside the cylinder. As illustrated the drive piston 3 is driven by an eccentric 4, and on a working stroke its surface 17 engages a corresponding surface 18 on the valve sleeve 15. Further downward movement of the drive piston effects a working stroke of the hammer piston 8. The piston 3 and cylinder include respectively an annular projection 24 and a bore, adapted to receive the projection, of greater diameter than the bore of the cylinder in which the sleeve slides. Therefore downward movement of the projection 24 causes the pressure acting on the upper surface 25 of the sleeve to increase. Thus at a predetermined position of the drive piston, the sleeve is displaced relative to the drive piston to open the return passageways 19, and the liquid flows back into a chamber 2a. Passageways 12 communicate with the chamber 2a. Alternatively (Fig. 3, not shown) the valve sleeve has a cam surface which co-operates with a cam on the eccentric such that the sleeve is displaced relative to the drive piston to permit pressure liquid within the cylinder to return to the chamber 2a. The tool has mechanism (Fig. 2) including a fluid or friction coupling 45, whereby a tool bit holder 43 may be continuously rotated during percussive action by means of a worm drive 40-43. Means, including a fan, is also provided for the introduction of pressure air into the space below the hammer piston 8. Reference has been directed by the Comptroller to Specification 915,496. |
