Impact buffer for impact drive tools

Claim 1

In an impact drive tool for driving nails or similar articles having a percussive piston mounted for movement in a cylinder, means for directing a pressure medium into one end of the cylinder to initiate an impact stroke driving the piston toward the other end of the cylinder, and impact buffer means positioned to absorb driving energy at the end of the impact stroke, wherein said buffer means comprise a first buffer element secured to said piston to face the other end of the cylinder, and a second buffer element secured to the other end of the cylinder, the improvement wherein said first buffer element comprises a material having an open cell structure in which the open cells are distributed substantially uniformly whereby the volume of said first buffer element is compressible, wherein said second buffer element comprises an elastic material which is harder than the material of the first buffer element, wherein said percussive piston has a surface facing toward said other end of said cylinder, said first buffer element having a portion projecting toward said other end of said cylinder past said piston surface, said second buffer element having a cavity open toward said percussive piston and a ring surface surrounding said cavity and positioned to be struck by said surface of said piston, said ring surface of said second buffer element having radially extending grooves, said cavity in the second buffer element being positioned so that the first buffer element is compressed in said cavity prior to the piston reaching its work stroke end position in which the piston impacts on said annular surface of the second buffer element, the first buffer element substantially filling the available space of said cavity in said second buffer element when the piston has reached the end of said impact stroke, said radially extending grooves allowing escape of the air expelled from said open cell structure of the first buffer element.