US Patent 7428836 Door lock having reinforced strength

A door lock includes a support seat having a recess for mounting a driven member, a control knob including a drive member rotatably mounted in the support seat to rotate the driven member and a rotation member to rotate the drive member and having an outer wall formed with an annular groove and a locking groove, and a locking pin mounted in the support seat and having a locking end selectively extended into the annular groove or the locking groove of the rotation member of the control knob. Thus, the door lock has a dead locking function to lock the door from inside to prevent the door from being unlocked from outside by a key or other tool so as to protect the user's safety inside of the door.