Patent ID: 6152013
Filing Date: 2000-11-28
Classification: B25D

Abstract:
A hydraulically actuated breaker with a lost-motion preventing device, comprising:a breaker main body having a piston bore and a chisel insertion hole, and comprising a cylinder portion formed by a piston disposed in said piston bore to define a first chamber constantly communicated with a hydraulic pressure source and having a small pressure receiving area for upwardly moving said piston and a second chamber having a large pressure receiving area for downwardly moving said piston;a chisel inserted within said chisel insertion hole of said breaker main body in opposition to said piston;a main switching valve switchable between a first position communicating said second chamber with a tank and a second position communicating said second chamber with the hydraulic pressure source; anda valve mechanism for placing said main switching valve at said first position when said piston is in an effective lower stroke end position, placing said main switching valve at said second position when said piston is in an effective upper stroke end position, and maintaining said main switching valve at said second position when said piston is lowered beyond said effective lower stroke end position;wherein said main switching valve comprises a first pressure receiving portion for placing said main switching valve at said first position and a second pressure receiving portion for placing said main switching valve at said second position, and when said piston is lowered beyond said effective lower stroke end position, said valve mechanism communicates said first chamber and said first pressure receiving portion with said tank.